JP6512962B2 - Plasma processing system - Google Patents

Description

  The present invention relates to a technology for performing plasma processing on an object to be processed, and more particularly to a pulse modulation type plasma processing apparatus that modulates high frequency power used for plasma processing with a pulse of a constant frequency.

  In general, a plasma processing apparatus generates a plasma of a processing gas in a processing chamber capable of vacuum evacuation, and is disposed on a processing target object disposed in the processing container by a gas phase reaction or surface reaction of radicals or ions contained in the plasma. The thin film is deposited on the surface of the substrate, or the material or the thin film on the surface of the object to be treated is scraped.

  In the capacitive coupling type plasma processing apparatus, the upper electrode and the lower electrode are disposed in parallel in the processing container, the object to be treated (semiconductor wafer, glass substrate, etc.) is placed on the lower electrode, or the upper electrode or A high frequency of frequency (usually 13.56 MHz or more) suitable for plasma generation is applied to the lower electrode. By the application of the high frequency, electrons are accelerated by the high frequency electric field between the upper and lower electrodes, and plasma is generated by the collision ionization of the electrons and the processing gas. In addition, a high frequency of low frequency (usually 13.56 MHz or less) is applied to the lower electrode on which the object to be processed is placed, and ions in the plasma are accelerated by the negative bias voltage or sheath voltage generated on the lower electrode. Many RF bias methods are used. By the RF bias method, ions can be accelerated from the plasma and collide with the surface of the object to promote surface reaction, anisotropic etching, film modification, and the like.

  In recent years, in order to improve the yield and processing accuracy of dry etching, for example, charging damage (destruction of gate oxide film due to charge accumulation) is prevented or microloading effect (geometric structure of pattern or locality of pattern density) Technology has been widely used to modulate high frequency waves for generating plasma and / or high frequency waves for bias with pulses of a constant frequency in order to suppress the variation in the etching rate).

  Generally, in this type of pulse modulation, depending on the duty ratio of the modulation pulse, the power of the high frequency wave to be modulated is made to be a predetermined level during the pulse on period, and the power of the high frequency is in the pulse off period. To the zero level off state. Therefore, for example, in the case of pulse-modulating the power of high frequency waves for plasma generation, plasma is generated and etching progresses during the pulse on period, and the plasma disappears and the etching is suspended during the pulse off period. In this case, the matcher provided on the plasma generation high-frequency transmission line measures the load impedance during the pulse-on period of each cycle so that the load impedance measurement matches or approximates the match point (usually 50Ω). And variably control the reactance of the variable reactance element provided in the matching circuit.

Unexamined-Japanese-Patent No. 2012-9544 JP, 2013-33856, A

  As one form of pulse modulation in the above-described capacitive coupling type plasma processing apparatus, the power of the high frequency is controlled to a constant level, that is, a high level during the pulse-on period according to the duty ratio of the modulation pulse. There is a method of controlling the power of the high frequency to a constant low level lower than the high level during the off period. Here, the low level is chosen to be higher than the lowest level required to maintain the plasma generation state.

  In such a high / low pulse modulation system, a certain amount of electrons and ions of plasma and radicals remain in the processing container during the pulse-off period without disappearing. Taking advantage of this, control the chemical or physical action of electrons, ions and / or radicals on the surface of the object by setting the low level of the high frequency power and other process parameters to appropriate values. Thus, the effect of improving predetermined etching characteristics in a certain etching process is expected.

  However, in the high / low pulse modulation method, when the frequency of the modulation pulse is set to a high value (usually 1 kHz or more), variable control of the variable reactance element in the matching unit can not follow the modulation pulse. For this reason, it is necessary to align only in the pulse high period which mainly contributes to the plasma process, and to exclude the secondary pulse low period from the target of the alignment. Then, a large reflected wave is generated on the high frequency feed line during the pulse low period in which the matching can not be achieved at all. This makes it difficult to control the high frequency power to be stable and accurate at a preset low level, which in turn reduces the expected effects of the process in the high / low pulse modulation method and increases the load on the high frequency power supply etc. .

  The present invention solves the problems of the prior art as described above, and alternately switches between high level and low level power of high frequency power used for plasma processing according to the duty ratio of modulation pulse (especially at high speed) The present invention provides a plasma processing apparatus capable of efficiently utilizing a pulse modulation method to be switched as expected.

  The plasma processing apparatus of the present invention generates a plasma by high frequency discharge of processing gas in a vacuum-evacuable processing container that accommodates the object to be processed in and out, and the object to be processed in the processing container under the plasma. Plasma processing apparatus which performs desired processing in the first period, and in the first period and the second period alternately repeating the first high frequency power source outputting the first high frequency and the constant duty ratio, in the first period The output of the first high frequency power supply is set to a constant frequency so that the power of the first high frequency becomes high level and the power of the first high frequency becomes low level lower than the high level in the second period. A first high frequency power modulation unit that modulates with a modulation pulse, and a first electrode disposed in or around the processing container for the first high frequency output from the first high frequency power supply Measuring the impedance of the load seen from the first high frequency power supply on the first high frequency power supply line for transmission at the first frequency, and the measured value of the load impedance in the first period, and And a first matching device for matching a weighted average measurement value obtained by weighted averaging the load impedance measurement values in the second period with a desired weight to the output impedance of the first high frequency power supply.

  In the above-described apparatus configuration, the balance between the reflected wave power in the pulse high period and the reflected wave power in the pulse low can be arbitrarily controlled by adjusting the value of the weighted variable of the weighted average. By this, the power of the reflected wave in the high / low period can be arbitrarily reduced, and the load power can be set to a higher value arbitrarily to meet the process requirement. In addition, the burden of a circulator or the like for protecting the high frequency power source from reflected waves and the ability to withstand reflected waves of the high frequency power source itself can be reduced, and hardware simplification and power consumption efficiency can be achieved around the high frequency power source. .

  According to the plasma processing apparatus of the present invention, the high frequency power used for plasma processing alternates between the high level and the low level according to the duty ratio of the modulation pulse (especially at high speed) by the above configuration and operation. ) The pulse modulation method to be switched can be realized efficiently as expected.

FIG. 1 is a cross-sectional view showing a configuration of a dual frequency superimposed capacitive coupling type plasma processing apparatus in an embodiment of the present invention. It is a wave form diagram showing a typical combination of a waveform of each part in the case of performing pulse modulation of high / low to a high frequency for plasma generation. It is a block diagram which shows the structure of the high frequency power supply for plasma production, and a matching device. It is a block diagram which shows one structural example of the impedance sensor with which the matching device of FIG. 3 is equipped. It is a block diagram which shows another structural example of the said impedance sensor. FIG. 7 is a Smith chart diagram showing the matching operation when the weight variable K of the weighted average operation is selected as K = 1 in the embodiment. It is a Smith chart figure which shows a matching effect when the weight variable K of a weighted-average calculation is selected to 0.5 <K <1. It is a wave form diagram which shows the waveform of each part when it selects to K = 1. It is a wave form diagram which shows the waveform of each part when it selects to 0.5 <K <1. It is a block diagram which shows the structure in the high frequency output control part of FIG. It is a block diagram which shows the structure of RF power monitor of FIG. 7, and a power supply control part. It is sectional drawing for demonstrating the HARC process in an Example. It is a graph which shows the pulse off period dependency of one process characteristic (etching amount) obtained by the 1st experiment of an Example. It is a graph which shows the pulse-off period dependence of one process characteristic (necking CD) obtained by 1st experiment. It is a graph which shows the pulse off period dependence of one process characteristic (intermediate Ox Boeing CD) obtained by the 1st experiment. It is a graph which shows the pulse-off period dependence of one process characteristic (selection ratio) obtained by the 1st experiment. It is a graph which shows the pulse off period dependency of one process characteristic (aspect ratio change rate) obtained by the 1st experiment. It is a graph which shows the upper DC voltage dependence of one process characteristic (etching amount) obtained by the 2nd experiment of an Example. It is a graph which shows the upper DC voltage dependence of one process characteristic (necking CD) obtained by 2nd experiment. It is a graph which shows the upper DC voltage dependence of one process characteristic (intermediate Ox Boeing CD) obtained by the 2nd experiment. It is a graph which shows the upper DC voltage dependence of one process characteristic (selectivity) obtained by the 2nd experiment. It is a graph which shows the upper DC voltage dependence of one process characteristic (aspect ratio change rate) obtained by the 2nd experiment. It is a graph which shows the relationship between the load power which can be set in a high frequency electric-power, and reflected wave power. It is a figure for demonstrating the mechanism in which the abnormal discharge inside the upper electrode generate | occur | produces, when performing pulse modulation of ON / OFF with respect to both the high frequency for plasma production, and the high frequency for ion drawing-in. In order to explain the mechanism that abnormal discharge inside the upper electrode does not occur when applying high / low pulse modulation to high frequency for plasma generation and on / off pulse modulation to high frequency for ion attraction FIG. FIG. 7 is a view showing an example of monitor information obtained when abnormal discharge occurs in the upper electrode in the plasma processing apparatus of FIG. 1; FIG. 7 is a diagram showing an example of monitor information obtained when abnormal discharge does not occur inside the upper electrode in the plasma processing apparatus of FIG. 1. It is a figure which shows the result of one experiment conducted about the presence or absence of generation | occurrence | production of the abnormal discharge inside the upper electrode in the plasma processing apparatus of FIG.

Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings.

[Configuration of plasma processing apparatus]

  FIG. 1 shows the configuration of a plasma processing apparatus according to an embodiment of the present invention. This plasma processing apparatus is configured as a capacitively coupled (parallel plate type) plasma etching apparatus of lower two high frequency superposition application type, for example, a cylindrical vacuum chamber made of aluminum whose surface is alumite treated (anodized). (Processing container) 10 is provided. The chamber 10 is grounded.

  A cylindrical susceptor support 14 is disposed on the bottom of the chamber 10 via an insulating plate 12 made of ceramic or the like, and a susceptor 16 made of, for example, aluminum is provided on the susceptor support 14. The susceptor 16 constitutes a lower electrode, on which a semiconductor wafer W, for example, is placed as an object to be processed.

  An electrostatic chuck 18 for holding the semiconductor wafer W is provided on the upper surface of the susceptor 16. The electrostatic chuck 18 sandwiches an electrode 20 made of a conductive film between a pair of insulating layers or insulating sheets, and a DC power source 24 is electrically connected to the electrode 20 through a switch 22. The semiconductor wafer W can be held on the electrostatic chuck 18 by the electrostatic attraction force by the DC voltage from the DC power supply 24. A focus ring 26 made of, for example, silicon is disposed on the upper surface of the susceptor 16 around the electrostatic chuck 18 to improve etching uniformity. A cylindrical inner wall member 28 made of, for example, quartz is attached to the side surfaces of the susceptor 16 and the susceptor support 14.

  Inside the susceptor support 14, for example, a coolant chamber 30 extending in the circumferential direction is provided. A refrigerant having a predetermined temperature, for example, cooling water (cw) is circulated and supplied to the refrigerant chamber 30 from an external chiller unit (not shown) via the pipes 32a and 32b. The processing temperature of the semiconductor wafer W on the susceptor 16 can be controlled by the temperature of the refrigerant. Furthermore, a heat transfer gas such as He gas from a heat transfer gas supply mechanism (not shown) is supplied between the upper surface of the electrostatic chuck 18 and the back surface of the semiconductor wafer W via the gas supply line 34.

The susceptor 16 is electrically connected to high frequency power supplies 36 and 38 via matching units 40 and 42 and a common feed conductor (for example, feed rod) 44. One high frequency power supply 36 outputs high frequency HF of a constant frequency f _HF (for example, 40 MHz) suitable for generating a plasma. The other high frequency power supply 38 outputs a high frequency LF of a constant frequency f _LF (for example, 12.88 MHz) suitable for attracting ions from the plasma to the semiconductor wafer W on the susceptor 16.

  As described above, the matching unit 40 and the feed rod 44 constitute a part of the high frequency feed line (high frequency transmission line) 43 for transmitting the high frequency HF for plasma generation from the high frequency power source 36 to the susceptor 16. On the other hand, the matching unit 42 and the feed rod 44 constitute a part of a high frequency feed line (high frequency transmission line) 45 for transmitting the high frequency LF for ion attraction from the high frequency power supply 38 to the susceptor 16.

  An upper electrode 46 is provided on the ceiling of the chamber 10 so as to face in parallel with the susceptor 16. The upper electrode 46 includes an electrode plate 48 having a large number of gas injection holes 48a and made of a silicon-containing material such as Si or SiC, and a conductive material for detachably supporting the electrode plate 48, such as aluminum whose surface is alumite treated And an electrode support 50 consisting of A processing space or plasma generation space PA is formed between the upper electrode 46 and the susceptor 16.

  The electrode support 50 has a gas buffer chamber 52 inside, and a large number of gas vents 50 a communicating with the gas injection holes 48 a of the electrode plate 48 from the gas buffer chamber 52 on the lower surface thereof. A processing gas supply source 56 is connected to the gas buffer chamber 52 via a gas supply pipe 54. The processing gas supply source 56 is provided with a mass flow controller (MFC) 58 and an on-off valve 60. When a predetermined processing gas (etching gas) is introduced into the gas buffer chamber 52 from the processing gas supply source 56, the plasma generation space PA is processed toward the semiconductor wafer W on the susceptor 16 from the gas ejection holes 48a of the electrode plate 48. Gas is spouted like a shower. Thus, the upper electrode 46 doubles as a shower head for supplying the processing gas to the plasma generation space PA.

  In addition, a passage (not shown) through which a coolant such as cooling water flows is also provided inside the electrode support 50, and the entire upper electrode 46, in particular the electrode plate 48, has a predetermined temperature via the coolant by an external chiller unit. The temperature is adjusted to Furthermore, in order to further stabilize the temperature control on the upper electrode 46, a configuration (for example, a heater (not shown)) made of a resistive heating element may be attached to the inside or the top of the electrode support 50.

In this embodiment, a DC power supply unit 62 for applying a negative DC voltage V _dc to the upper electrode 46 is provided. For this purpose, the upper electrode 46 is electrically floatingly attached to the top of the chamber 10 via the ring-shaped insulator 64. Ring insulator 64 is made of, for example, alumina (Al ₂ O ₃ ), and airtightly seals the gap between the outer peripheral surface of upper electrode 46 and the side wall of chamber 10, and upper electrode 46 is physically grounded. In favor of

The DC power supply unit 62 includes two DC power supplies 66 and 68 having different output voltages (absolute values), and a switch 70 for selectively connecting the DC power supplies 66 and 68 to the upper electrode 46. DC power supply 66 outputs a negative DC voltage V _dc1 (for example, -2000 to -1000 V) having a relatively large absolute value, and DC power supply 68 a negative DC voltage V _dc2 (for example, a relatively small absolute value) Output -300 to 0V). The switch 70 operates in response to the switching control signal SW from the main control unit 72, and connects the DC power supply 66 to the upper electrode 46 and the second switch position to connect the DC power supply 68 to the upper electrode 46. It switches between switch positions. Furthermore, the switch 70 may have a third switch position that disconnects the upper electrode 46 from either of the DC power supplies 66, 68.

The filter circuit 76 provided in the middle of the DC power supply line 74 between the switch 70 and the upper electrode 46 passes the DC voltage V _dc1 (V _dc2 ) from the DC power supply 62 as it is and applies it to the upper electrode 46 The high frequency coming from the susceptor 16 through the processing space PA and the upper electrode 46 and entering the DC feed line 74 is made to flow to the ground line and not to the DC power supply 62 side.

  Further, a DC ground part (not shown) made of a conductive material such as Si, SiC or the like is attached to an appropriate position facing the plasma generation space PA in the chamber 10. The DC ground part is always grounded via a ground line (not shown).

  An annular space formed between the susceptor 16 and the susceptor support 14 and the side wall of the chamber 10 is an exhaust space, and the exhaust port 78 of the chamber 10 is provided at the bottom of the exhaust space. An exhaust device 82 is connected to the exhaust port 78 via an exhaust pipe 80. The exhaust device 82 has a vacuum pump such as a turbo molecular pump so that the inside of the chamber 10, in particular, the plasma generation space PA can be depressurized to a desired degree of vacuum. Further, on the side wall of the chamber 10, a gate valve 86 for opening and closing the loading / unloading port 84 of the semiconductor wafer W is attached.

  The main control unit 72 includes one or more microcomputers, and in accordance with software (program) and recipe information stored in the external memory or the internal memory, the respective units in the apparatus, particularly the high frequency power supplies 36, 38, the matching unit 40. , 42, the MFC 58, the open / close valve 60, the DC power supply unit 62, the exhaust device 82 and the like, and control the operation (sequence) of the entire device.

  The main control unit 72 also stores an operation panel (not shown) for a man-machine interface including an input device such as a keyboard and a display device such as a liquid crystal display, and various data such as various programs and recipes and setting values. Alternatively, it is also connected to an external storage device (not shown) or the like that stores data. In this embodiment, the main control unit 72 is shown as one control unit, but a plurality of control units may share the functions of the main control unit 72 in parallel or hierarchically.

  The basic operation of single wafer dry etching in this capacitively coupled plasma etching apparatus is performed as follows. First, the gate valve 86 is opened, the semiconductor wafer W to be processed is loaded into the chamber 10 and mounted on the electrostatic chuck 18. Then, a processing gas, that is, an etching gas (generally a mixed gas) is introduced into the chamber 10 from the processing gas supply source 56 at a predetermined flow rate and flow ratio, and the pressure in the chamber 10 is set to a set value by evacuation using . Further, a high frequency power HF (40 MHz) for plasma generation and a high frequency power LF (12.88 MHz) for ion attraction are superimposed on predetermined power from the high frequency power supplies 36 and 38 and applied to the susceptor 16. Further, a DC voltage is applied from the DC power supply 24 to the electrode 20 of the electrostatic chuck 18 to fix the semiconductor wafer W on the electrostatic chuck 18. The etching gas discharged from the shower head of the upper electrode 46 is discharged under the high frequency electric field between the two electrodes 46 and 16 to generate plasma in the processing space PA. The film to be processed on the main surface of the semiconductor wafer W is etched by radicals or ions contained in the plasma.

In this plasma etching apparatus, the power of the high frequency power HF for plasma generation output from the high frequency power supply 36 is, for example, a modulation pulse having a constant frequency f _S and a variable duty ratio D _S selected within the range of 1 kHz to 50 kHz. The first (plasma generation system) power modulation scheme modulated by MS can be used for a given etch process.

  The first power modulation method has two modes of on / off pulse modulation and high / low pulse modulation. Here, the on / off pulse modulation is performed during the pulse-off period by setting the power of high frequency HF for plasma generation to a predetermined level during the pulse-on period according to the duty ratio of the modulation pulse MS. Sets the high frequency HF power to the zero level off state. On the other hand, for high / low pulse modulation, the power of high frequency HF is controlled to high level during the pulse on period according to the duty ratio of the modulation pulse MS, and the power of high frequency HF is high level during the pulse off period. Control to a lower low level. However, the low level is chosen to be higher than the lowest level required to maintain the plasma generation state. Also, the low level is usually selected to a value (1/2 or less) that is clearly lower than the high level.

  Further, in this plasma etching apparatus, a second (ion drawing system) power modulation method is used for a given etching process, in which the power of the high frequency power LF for ion attraction output from the high frequency power supply 38 is modulated by the modulation pulse MS. It is also possible. Similar to the first power modulation scheme, the second power modulation scheme also has two types of modes: on / off pulse modulation and high / low pulse modulation.

FIG. 2 shows an example of the waveform of each part when pulse modulation is performed synchronously and simultaneously in both the plasma generation system and the ion attraction system. As illustrated, the period T _C of the modulated pulse MS, the pulse-on period (first period) T _on and pulse-off period between the (second _{period) T off, T C = T} on + T off Relationship. Assuming that the frequency of the modulation pulse MS is f _S , T _C = 1 / f _S and the duty ratio D _S is D _S = T _on / (T _on + T _off ).

In the illustrated example, high / low pulse modulation is applied to high frequency HF for plasma generation, and on / off pulse modulation is applied to high frequency LF for ion attraction. Furthermore, the DC voltage V _dc applied to the upper electrode 46 from the DC power supply 62 can be synchronized with the modulation pulse MS. Applied in the illustrated example, to the upper electrode 46, the pulse-on period T during _on applies a low DC voltage V _dc2 absolute value, the pulse-off period during T _off is a greater direct voltage V _dc1 absolute value Do.

[Configuration of high frequency power supply and matching device]

  FIG. 3 shows the configuration of the high frequency power supply 36 and the matching unit 40 of the plasma generation system in this embodiment.

  The high frequency power supply 36 can control the power of the basic high frequency power output from the RF oscillator 90A and an RF oscillator 90A that generates a basic high frequency of a constant frequency (for example, 40 MHz) suitable for plasma generation having a sinusoidal waveform in general. And a power control unit 94A for directly controlling the RF oscillator 90A and the power amplifier 92A in accordance with a control signal from the main control unit 72. The main control unit 72 supplies the power control unit 94A with not only control signals instructing the output mode of RF and modulation pulses MS, but also control signals such as normal power on / off and power interlock relationship, power setting values, etc. Data is also given. When pulse modulation (especially high / low pulse modulation) is performed on the high frequency power HF for plasma generation, the power control unit 94A configures a pulse modulation unit under the control of the main control unit 72.

  An RF power monitor 96A is also provided in the high frequency power supply 36 unit. Although not shown, the RF power monitor 96A has a directional coupler, a traveling wave power monitor, and a reflected wave power monitor. Here, the directional coupler takes out a signal corresponding to each of the power of the traveling wave propagating in the forward direction on the high frequency feed line 43 and the power of the reflected wave propagating in the opposite direction. The traveling wave power monitor unit generates a traveling wave power measurement value signal representing the power of the traveling wave included in the traveling wave on the high frequency feed line 43 based on the traveling wave power detection signal extracted by the directional coupler. . This traveling wave power measurement value signal is supplied to the power supply control unit 94A in the high frequency power supply 36 for power feedback control, and is also supplied to the main control unit 72 for monitor display. The reflected wave power monitor unit measures the power of the reflected wave returned from the plasma in the chamber 10 to the high frequency power supply 36. The reflected wave power measurement value obtained from the reflected wave power monitor unit is given to the main control unit 72 for monitor display and also given to the power control unit 94A in the high frequency power supply 36 as a monitor value for protecting the power amplifier.

Matching unit 40 includes matching circuit 98A including a plurality of, for example, two controllable reactance elements (for example, variable capacitors or variable inductors) X _H1 and X _H2 connected to high frequency feed line 43, and reactance elements X _H1 and X _H2. The matching controller 104A controls the reactance of the motor via an actuator such as a motor (M) 100A, 102A, the impedance sensor 106A measures the impedance of the load including the impedance of the matching circuit 98A on the high frequency feed line 43, and the matching circuit 98A. It has a V _pp detector 107A for measuring the peak / peak value V _pp of the high frequency HF on the high frequency feed line 43 at the output terminal side. The internal configuration and operation of the impedance sensor 106A and the role of the V _pp detector 107A will be described in detail later.

The high-frequency power supply 38 (FIG. 1) of the ion pull-in system also has the RF oscillator 90B, the power amplifier 92B, and the power control unit in the same manner as the high-frequency power supply 36 of the plasma generation system described above A power supply 96B (not shown) and a power monitor 96B are provided. Further, the matching unit 42 also has the matching circuit 98B, the motors (M) 100B and 102B, the matching controller 104B, the impedance sensor 106B and the V _pp detector 107B (not shown) as well as the matching unit 40 of the plasma generation system. doing.

[Configuration of impedance sensor]

  FIG. 4A shows one configuration example of the impedance sensor 106A provided in the matching unit 40 of the plasma generation system. The impedance sensor 106A includes an RF voltage detector 110A, an RF current detector 112A, a load impedance instantaneous value calculation circuit 114A, an arithmetic average value calculation circuit 116A, a weighted average value calculation circuit 118A, and a moving average value calculation circuit 120A.

  The RF voltage detector 110A and the RF current detector 112A detect the voltage and current of the high frequency HF on the high frequency feed line 43, respectively. Load impedance instantaneous value calculation circuit 114A calculates instantaneous value JZ of load impedance Z on high frequency feed line 43 based on voltage detection signal JV and current detection signal JI obtained from RF voltage detector 110A and RF current detector 112A, respectively. Calculate The load impedance instantaneous value calculation circuit 114A may be an analog circuit, but is preferably configured by a digital circuit.

Arithmetic mean value calculating circuit 116A, when the pulse modulation of the high / low is subjected to high-frequency HF for plasma generation, modulation pulse in each cycle of the MS, the pulse-on period T load impedance in _on the instantaneous value calculation circuit 114A the instantaneous value JZ more resulting load impedance Z by sampling at a predetermined sampling frequency f _C, with the computing the arithmetic mean value aZ _on the load impedance Z in the pulse-on period T _on, the pulse-off period T _off during load impedance instantaneous values instantaneous value JZ load impedance Z obtained from the arithmetic circuit 114A is sampled at the sampling frequency f _C, calculates the arithmetic mean value aZ _off of the load impedance Z in the pulse-off period T _off to.

However, if the pulse modulation of the on / off is subjected to high-frequency HF for plasma generation, the arithmetic mean value calculating circuit 116A in each cycle of the modulation pulses MS, the load impedance instantaneous value calculation only during the pulse-on period T _on the instantaneous value JZ load impedance Z obtained from the circuit 114A is sampled at the predetermined sampling frequency f _C, calculates the arithmetic mean value aZ _on the load impedance Z in the pulse-on period T _on.

The main control unit 72 (FIG. 1) provides a monitor signal JS to specify the sampling time or monitoring time in synchronism with the modulation pulses MS, and a clock CK ₁ for sampling the arithmetic mean value calculating circuit 116A. Here, when high / low pulse modulation is applied to the high frequency HF for plasma generation, the monitor signal JS has monitor times T ₁ and T ₁ to be described later in both the pulse on period _Ton and the pulse off period T _{off. 2} were respectively designated, when the pulse modulation on / off is subjected to high-frequency HF specifies only monitoring period T ₁ of the pulse-on period T _on. Arithmetic mean value calculating circuit 116A, since the required high-speed and large amount of signal processing in synchronization with the sampling clock CK ₁ number 10MHz, it is possible to use a FPGA (Field Programmable Gate Array) suitably.

The weighted average value arithmetic circuit 118A is preferably constituted by a CPU, and when high frequency / low frequency pulse modulation is applied to high frequency HF for plasma generation, the pulse on period T obtained by the arithmetic average value arithmetic circuit 116A. the arithmetic mean value aZ _off of the load impedance Z in the arithmetic average aZ _on and pulse-off period T _off of the load impedance Z in _on the weighted average in the desired weight (weighting variables K), 1 cycle of the load impedance The weighted average value bZ of The main control unit 72 supplies the weight variable K and the clock CK ₂ for weighted average calculation to the weighted average value calculation circuit 118A.

However, if the pulse modulation of the on / off is subjected to high-frequency HF is the weighted average value calculating circuit 118A does not function, the arithmetic load impedance Z in the pulse-on period T _on output from the arithmetic mean value calculating circuit 116A The average value aZ _on is sent to the subsequent moving average value calculation circuit 120A without passing through the weighted average value calculation circuit 118A.

  The moving average calculation circuit 120A is preferably configured by a CPU, and when high frequency HF for plasma generation is subjected to high / low pulse modulation, a plurality of continuous loads obtained from the weighted average calculation circuit 118A are used. The movement weighted average value cZ of the load impedance Z is calculated based on the one cycle weighted average value bZ of the impedance Z, and the movement weighted average value cZ is output as the measured value MZ of the load impedance Z.

Further, the moving average value computation circuit 120A, when the pulse modulation of the on / off is subjected to high-frequency HF, the load impedance Z in a plurality of pulse-on period T _on a continuous output from the arithmetic mean value calculating circuit 116A The moving average value dZ is calculated _on the basis of the arithmetic average value aZ _on , and the moving average value dZ is output as the measured value MZ of the load impedance Z. The main control unit 72 supplies the set values of the movement section L and the movement pitch P and the clock CK ₃ to the moving average value calculation circuit 120A.

Measurements MZ of the load impedance outputted from the moving average value computation circuit 120A is updated in synchronization with the clock CK _3. Usually, the load-side impedance measurement value MZ includes the absolute value of the load impedance Z and the measurement value of the phase.

FIG. 4B shows another configuration example of the impedance sensor 106A. As shown, it is also possible to provide the weighted average value calculation circuit 118A in the subsequent stage of the moving average value calculation circuit 120A. In this configuration example, when high / low pulse modulation is applied to high frequency HF for plasma generation, moving average value calculation circuit 120A is a plurality of (n) consecutive ones obtained from arithmetic average value calculation circuit 116A. based on the pulse-on period T load in _on impedance Z arithmetic mean aZ _off of the load impedance Z in the arithmetic average aZ _on and pulse-off period T _off of the movement of the load impedance Z in the pulse-on period T _on It calculates a moving average value eZ _off of the load impedance Z in the average value eZ _on and pulse-off period T _off.

Weighted mean value calculating circuit 118A, the moving average value eZ of the load impedance Z in the moving average value eZ _on and pulse-off period T _off of the load impedance Z in obtained from the moving average value computation circuit 120A pulse-on period T _on The weighted moving average value fz of the load impedance Z is obtained by weighted averaging of _off with the desired weight (weighting variable K), and the weighted moving average value fz is output as the load impedance measurement value Mz.

However, if the pulse modulation of the on / off is subjected to high-frequency HF for plasma generation, weighted mean value calculating circuit 118A does not work, the load in the pulse-on period T _on output from the moving average value computation circuit 120A The moving average value eZ _on of the impedance Z is output as the load impedance measurement value MZ as it is.

Similarly to the impedance sensor 106A in the matching unit 40 of the plasma generation system described above, the matching unit 42 (FIG. 1) of the ion pull-in system also includes the RF voltage detector 110B, the RF current detector 112B, and the load impedance instantaneous value calculation circuit 114B. , An arithmetic mean value calculation circuit 116B, a weighted average value calculation circuit 118B, and a moving average value calculation circuit 120B, and an impedance sensor 106B (not shown). Also in the impedance sensor 106B, the weighted average value arithmetic circuit 118B and the moving average value arithmetic circuit 120B are similarly operated according to the pulse modulation mode (high / low or on / off) applied to the high frequency LF for ion attraction. Signal processing is switched.

[Function of matching device]

  Here, the operation of the matching unit 40 of the plasma generation system in the case where high / low pulse modulation is applied to the power of high frequency HF for plasma generation will be described. It is assumed that on / off pulse modulation is applied to the power of the high frequency LF for ion attraction under the same modulation pulse MS.

In this case, on the high frequency power supply line 43 of the plasma generation system, also sustained pulse off period T _off during not high frequency HF from the high frequency power source 36 toward the plasma load within the chamber 10 only during the pulse-on period T _on Transmitted to However, since the power of the high frequency LF is turned on / off in synchronization with the duty ratio of the modulation pulse MS in the ion lead-in system, the plasma load visible from the matching unit 40 of the plasma generation system has a pulse on period _Ton and a pulse off period. It changes greatly with T _off . Therefore, when the frequency of the modulation pulse MS is set to a high value (usually 1 kHz or more), in the matching unit 40 of the plasma generation system, the reactance of the reactance elements X _H1 and X _H2 is controlled through the motors 100A and 102A under the control of the matching controller 104A. The variable auto-matching operation can not follow the modulation pulse MS.

In this embodiment, even if the frequency of the modulation pulse MS is increased to such an extent that the auto matching operation of the matching unit 40 can not follow, the pulse on period _Ton and the pulse can be obtained by special signal processing in the impedance sensor 106A as described later. The high or low pulse modulation can be operated effectively and stably by adjusting the balance of the matching or the degree of _misalignment with the off period T _off .

In this case, the main control unit 72 alternately switches the high level power preset according to the duty ratio of the modulation pulse MS and the low level power preset according to the duty ratio of the modulation pulse MS for the high frequency power supply 36 of the plasma generation system. A predetermined control signal, a set value, and a timing signal are supplied to the power supply control unit 94A so as to output a high frequency HF which is repeated. Then, with respect to impedance sensor 106A in matching unit 40, main control unit 72 monitors signal JS necessary for pulse modulation of high / low, weight variable K, set values L and P for moving average value calculation, and Clocks CK ₁ , CK ₂ and CK ₃ are given.

On the other hand, the main control unit 72 sets the power of the high frequency LF to the on level (on state) and the zero level (off) preset according to the duty ratio of the modulation pulse MS for the high frequency power supply 38 of the ion drawing system. The power supply control unit 94B is supplied with predetermined control signals, set values, and timing signals so that the state (a) is alternately repeated. Then, with respect to the impedance sensor 106B in the matching unit 42, the main control unit 72 monitors the monitor signal JS necessary for on / off pulse modulation, the set values L and P for calculating the moving average value, and the clocks CK ₁ , Give CK ₂ and CK ₃ . However, the weight variable K is not given.

In the matching unit 40 of the plasma generation system, as shown in FIG. 6A or 6B, the monitor times T ₁ and T ₂ are within the pulse on period _Ton and the pulse off period _Toff in each cycle of the modulation pulse MS. Are set respectively. Preferably, the pulse-on period T in _on, high frequency power supply line 43 on the monitor to start immediately and excluding immediately before the end of the transient time interval the power of the reflected wave changes abruptly time T ₁ is set. Similarly, a pulse-off within the time T _off, the monitor time T ₂ is set to excluding the transient time immediately after and immediately before the end start section.

Arithmetic mean value calculating circuit in the impedance sensor 106A 116A in each cycle of the modulation pulses MS, samples the instantaneous value JZ load impedance Z obtained from the pulse-on period T _on the load impedance instantaneous value calculating circuit 114A clocks CK ₁ in sampling, and calculating the arithmetic mean value aZ _on the load impedance Z in the pulse-on period T _on, the instantaneous value JZ load impedance Z obtained from the pulse-off period T _off load impedance instantaneous value calculating circuit 114A in Are sampled by the sampling clock CK ₁ to calculate the arithmetic mean value aZ _off of the load impedance Z in the pulse off period T _off .

Weighted mean value calculating circuit 118A has an arithmetic mean value of the load impedance Z in the arithmetic average aZ _on and pulse-off period T _off of the load impedance Z in the pulse-on period T _on obtained from the arithmetic average computing circuit 116A aZ A weighted average value bZ of one cycle of the load impedance is obtained by weighted averaging of _off and the desired weight (weight variable K). Here, the weight variable K is selected to an arbitrary value in the range of 0 ≦ K ≦ 1, and the weighted average value bZ is expressed by the following equation (1).
bZ = K * aZ _on + (1-K) * aZ _off (1)

When the high frequency HF for plasma generation is subjected to high / low pulse modulation, the moving average value calculation circuit 120A generates a plurality of (n) continuous load impedances Z obtained from the weighted average value calculation circuit 118A. Based on the one-cycle weighted average value bZ, the movement weighted average value cZ of the weighted average value bZ is calculated at a predetermined movement segment L and movement pitch P which are set in advance. For example, the modulation when the pulse MS of the frequency f _S is 1000 Hz, and sets the movement section L to 10 msec, when setting the movement pitch P to 2msec is 10 1 cycle weighted average successive every 2msec bZ One moving average value cZ is calculated for.

The moving average value calculation circuit 120A outputs the moving weighted average value cZ as a load impedance measurement value MZ. The load impedance measurements MZ depends on the value of the weighting variables K given to weighted mean value calculating circuit 118A from the main control unit 72 does not depend on the duty ratio D _S of the modulation pulse MS.

Matching controller 104A of the matching device 40 is responsive to be follow the load impedance measurements MZ which from moving average value computation circuit 120A of the impedance sensor 106A is output in the cycle of the clock CK _3, the phase of the load impedance measurements MZ is zero (0), the motor 100A, 102A is drive-controlled so that the absolute value becomes 50Ω, that is, it matches or approximates the matching point Z _S, and the reactance of the reactance elements X _H1 , X _H2 in the matching circuit 98A Variable control.

Thus, in the matching unit 40, matching operation load impedance measurements MZ output from the impedance sensor 106A to match or approximate to the matching point Z _S is performed. That is, the load impedance measurement value MZ is the matching target point. Thus, the pulse-on period T arithmetic mean value of the load impedance Z in the arithmetic average aZ _on and pulse-on period T _off of the load impedance Z in _on aZ _off is matched points according to the value of the weighted average of weighting variables K Offset by the ratio of (1−K): K from Z _S.

Here, when the weight variable K given to the impedance sensor 106A of the matching unit 40 from the main control unit 72 is set to K = 1, the weight K with respect to aZ _on of the first term in the right side of the arithmetic expression (1) of the weighted average. There is the maximum value "1", the weight (1-K) becomes the minimum value, i.e. zero "0" for aZ _off of the second term. In this case, as shown in the Smith chart of FIG. 5A, the arithmetic mean value aZ _on the load impedance Z in the pulse-on period T _on is equal or close to the matching point Z _S. On the other hand, the arithmetic mean value aZ _off of the load impedance Z in the pulse-off period T _off is farthest offset from the matching point Z _S.

When such is set to K = 1, on the high frequency power supply line 43 of the plasma generation system, as shown schematically in the waveform diagram of FIG. 6A, during the pulse-on period T _on the take matching substantially completely and for that, the power PR _H of the reflected wave is hardly appear, power PF _H of the traveling wave is load power PL _H as, on the one hand, in the pulse-off period T _off, since the alignment is out largest, reflecting The wave power PR _L is very high, and the traveling wave power _P F _L is much higher than the load power _{P L L.}

In addition, regarding the control with respect to the power of the high frequency HF, the high frequency power supply 36 in this embodiment is PF control for keeping the power PF of the traveling wave constant, and a net input obtained by subtracting the power PR of the reflected wave from the power of the traveling wave PF. Either PL control to keep the power (load power) constant can be selectively performed. However, when applying a power to the pulse modulation of the high / low of the high frequency HF, to use a PL control that can be placed in a stable reliably load the low level of power set to a lower value in at least a pulse-off period T _off Is preferred. However, if PL control is used under the condition of K = 1, as in the prior art, the pulse off period T _off can not be matched at all, so the power PR _{L of the} reflected wave is as shown in FIG. It becomes extremely large.

In this embodiment, setting the weight variable K to 0.5 <K <1 can address the above problem. That is, in the case of 0.5 <K <1, the weight K for the first term azon is smaller than the maximum value “1” _on the right side of the above-described weighted average formula (1), and the second term The weight (1−K) for aZ _off of is larger than the minimum value “0”. Thus, as shown in the Smith chart of FIG. 5B, the arithmetic mean value aZ _on the load impedance Z in the pulse-on period T _on is offset from the matching point Z _S, the load at that offset by pulse-off period T _off arithmetic mean aZ _off of the impedance Z approaches the matching point Z _S.

Here, the matching point Z _S is located on a straight line (intermediate point) connecting load impedance measurement values (arithmetic mean values) aZ _on and aZ _off in both periods T _on and T _{off on the} Smith chart. Then, (the closer to or 0.5) as release than 1 the value of K, the load impedance measurements aZ _on the pulse-on period T _on is away from the matching point Z _S, the load impedance of the pulse-off period T _off measurements aZ _off approaches the matching point Z _S.

If this set of weighting variables K in 0.5 <K <1 As, as shown schematically in the waveform diagram of FIG. 6B, on the high frequency power supply line 43 of the plasma generation system, a pulse-on period T _on even while the reflected wave is generated at a constant power PR _H, power PR _L of the reflected wave in the pulse-off period T _off is reduced than in the case of K = 1 in. By adjusting the value of K, it is possible to arbitrarily control the balance between the reflected wave power PR _L in the reflected wave power PR _H and the pulse-off period T _off in the pulse-on period T _on.

As a result, the power PR _L of the reflected wave in the pulse off period T _off can be arbitrarily reduced, and the load power PL _L can be set to a higher arbitrary value to meet the process demand. In addition, the burden of a circulator or the like for protecting the high frequency power source 36 from reflected waves and the reflected wave resistance of the high frequency power source 36 itself are reduced, and simplification of hardware size and efficiency of power consumption are achieved around the high frequency power source 36. It can also be done. Furthermore, by reducing the power PR _{L of the} reflected wave, PL control for maintaining the net high frequency power (load power) PL input to the plasma load at a set value as described later can be performed more accurately and efficiently it can.

The weight variable K is not limited to the range of 0.5 <K ≦ 1 but may be set within the range of 0 ≦ K ≦ 0.5. In the case of K = 0.5, both the weight K for aZ _on of the first term and the weight (1-K) for aZ _off for the second term are 0 _on the right side of the arithmetic expression (1) of the weighted average. equals .5, although not shown, matching points to the midpoint between the load impedance measurements aZ _off pulse-on period T _on of the load impedance measurements aZ _on and pulse-off period T _off is on the Smith chart Z _S is located.

Also, when 0 ≦ K <0.5, the weight K for the first term aZ _{on and the} weight (1−K) for the second term aZ _{off in} the right side of the above-described weighted average formula (1) because even small load impedance measurements aZ _on in the pulse-on period T _on is made relatively far from the matching point Z _S, relative to the load impedance measurements aZ _off in the pulse-off period T _off is consistent point Z _S It is close to In this case, power PR _L of the reflected wave in the pulse-off period T _off is relatively small, the reflected wave power PR _H in pulse-on period T _on is relatively large.

Thus, in this embodiment, the modulation pulse MS independent of the duty ratio D _S of the reflected wave power in the pulse-on period T _on PR _H and the pulse-off period T reflection wave power in _off PR _L And the balance (or the degree of matching or non-matching) can be arbitrarily controlled. The main control unit 72 arbitrarily sets the weight variable K in the range of 0 ≦ K ≦ 1 in the process recipe, switches the weight variable K for each process, or sets the weight variable K in one process. It can be switched stepwise or continuously.

In the ion pull-in type matching unit 42, since the high frequency LF is subjected to on / off pulse modulation, the weight variable K is not given to the impedance sensor 106B from the main control unit 72 as described above, and the average value is averaged. The arithmetic circuit 118B does not function. Moving average value computation circuit 120B, the moving average based on the arithmetic mean value aZ _on the impedance Z in a plurality of pulse-on period T _on a continuous output from the arithmetic mean value calculating circuit 116B for each cycle of the clock CK ₁ The value dZ is calculated, and the moving average value dZ is output as the measured value MZ of the load impedance Z.

Matching controller 104B of the matching device 42 is responsive to be follow the load impedance measurements MZ which from moving average value computation circuit 120B of the impedance sensor 106B is output in the cycle of the clock CK _3, the phase of the load impedance measurements MZ is zero (0), drive control of motors 100B and 102B so that absolute value becomes 50Ω, that is, match or approximate match point Z _S , and reactance of reactance elements X _L1 and X _L2 in matching circuit 98 B Variable control. In this case, the arithmetic mean value aZ _on to the moving average value cZ _on always matching target point that the load impedance Z in the pulse-on period T _on.

[Configuration of main parts in power control unit]

  FIGS. 7 and 8 show the configuration of the main part in the power supply control unit 94A of the high frequency power supply 36 of the plasma generation system.

As shown in FIG. 7, the power supply control unit 94A has a load power measurement unit 122A and a high frequency output control unit 124A. Load power measuring section 122A from the traveling-wave power detection signal S _PF obtained from RF power monitor 96A and the reflected wave power detection signal S _PR, measured values M _PL of the load power PL to be inputted to the load (mainly plasma) (M _PL = S _PF −S _PR ) is obtained by calculation.

The load power measurement unit 122A may have any form of an analog operation circuit or a digital operation circuit. That may generate a load power measurements M _PL of the analog signal takes the difference between the progressive wave power detection signal of the analog S _PF and analog reflection wave power detection signal S _PR, or progressive wave power detection signal S taking the difference between the two _PF and reflected wave power detection signal S _PR after having converted into digital signals may be generated load power measurements M _PL of the digital signal.

The high frequency output control unit 124A, as shown in FIG. 8, includes a first control command value generation unit 126A for a pulse on period (first period) and a first control command value generation unit for a pulse off period (second period). and a second control command value generating unit 128A, a traveling wave power detection signal a first control command value C _on or second control command value for the S _PF from the first control command value generating portion 126A of the RF power monitor 96A Comparator 130A that generates comparison error ER _on or ER _off in comparison with second control command value C _off from generation unit 128A, and power according to comparison error ER _on or ER _off from this comparator 130A It has an amplifier control unit 132A that variably controls the gain or amplification factor of the amplifier 92, and a local controller 134A that controls each unit in the high frequency output control unit 124A.

Here, the first control command value generating unit 126A, the load power set value given from the main control unit 72 via the load power measurements M _PL and the controller 134A given from the load power measuring unit 122A PL _H (or PL enter the _on), to generate a first control command value C _on for feedback control applied to the power PF of the traveling wave during the pulse-on period T _on each cycle of the modulation pulse MS.

On the other hand, the second control command value generating unit 128A inputs the load power set value PL _L from the load power measurements M _PL and the controller 134A from the load power measuring unit 122A, pulse in each cycle of the modulation pulses MS off during T _off applied to the traveling wave power PF to generate a second control command value C _off for feedback control.

The first and second control command value generation units 126A and 128A may preferably be configured by digital circuits. In that case, the first and second control command values C _on and C _off can be output in the form of analog signals by providing digital-analog (D / A) converters in the respective output stages.

A first control command value C _on output from the first control command value generating unit 126A, and the second control command value C _off output from the second control command value generating unit 128A, the switching circuit 136A Are alternately applied to the comparator 130A. Switching circuit 136A operates under the control of the controller 134A, in each cycle of the modulation pulses MS, during the pulse-on period T _on the first control command value C _on from the first control command value generating unit 126A selected and transferred to the comparator 130A, and during the pulse-off period T _off is to forward to the comparator 130A selects the second control command value C _off from the second control command value generating unit 128A It has become.

Accordingly, the comparator 130A, in each cycle of the modulation pulses MS, pulse-on period during T _on the progressive wave power detection signal S _PF of the comparison error, that the first as compared to the first control command value C _on A comparison error ER _on (ER _on = C _on −S _PF ) is generated, and during the pulse off period T _off , the traveling wave power detection signal S _PF is compared with the second control command value C _off to compare It is adapted to generate a second comparison error _{ER off (ER off = C off} -S PF).

Amplifier control unit 132A, the controller operates under the control of 134A, in each cycle of the modulation pulses MS, during the pulse-on period T _on the gain of the power amplifier 92A as close to zero a first comparison error ER _on or the amplification factor variable control to control the output of the high frequency power source 36, during the pulse-off period T _off is variably controlled by the gain or amplification factor of the power amplifier 92A as close to zero a second comparison error ER _off Thus, the output of the high frequency power supply 36 is controlled.

A linear amplifier (linear amplifier) is preferably used for the power amplifier 92A. Also, for example, a differential amplifier is used for the comparator 130A. In the comparator 130A, a constant proportionality relation is established between the difference (C _on −S _PF ) or (C _off −S _PF ) of the input signal and the comparison error ER _on or ER _off of the output signal. Just do it.

The high-frequency power supply 38 of the ion lead-in system also has the same configuration and function as the power control unit 94A in the high-frequency power supply 36 of the above-described plasma generation system except that the frequency of the high frequency LF differs from the frequency of the high frequency HF And a high frequency output control unit 124B (not shown).

[Operation of PL control in the embodiment]

In the plasma processing apparatus of this embodiment, when both of the high frequency power supplies 36 and 38 supply the high frequency HF for plasma generation or the high frequency LF for ion attraction into the chamber 10, respectively, the load (mainly plasma PL power control can be performed to maintain the net high frequency power applied to V.sub.2), i.e., the load power PL, separately at the set value in the pulse on period _Ton and the pulse off period _Toff .

  The action of PL control in this embodiment will be described below in the case where high / low pulse modulation is applied to the power of high frequency HF for plasma generation. It is assumed that on / off pulse modulation is applied to the power of the high frequency LF for ion attraction under the same modulation pulse MS.

In this case, the main control unit 72 sends control signal necessary for high / low pulse modulation and data of load power set values PL _H and PL _{L to} the power control unit 94A of the high frequency power supply 36 of plasma generation system. And a modulation pulse MS as a timing signal for pulse modulation. Incidentally, PL _H is the first load power set value that specifies the level (high level) of the power of the high frequency HF in the pulse-on period T _on. On the other hand, PL _L is the second load power set value that specifies the level (low level) of the power of the high frequency HF in the pulse-off period T _off. The high frequency power supply 36 performs the following PL control on the high frequency HF outputted by pulse modulation of high / low from the power supply 36.

First, the load power setting values PL _H and PL _L from the main control unit 72 are set in the controller 134A in the high frequency output control unit 124A. The controller 134A supplies the load power setting values PL _H and PL _L and required control signals and clock signals to the first and second control command value generating units 126A and 128A.

First control command value generating unit 126A, in each cycle of the modulation pulses MS, used in the feedback signal takes in the load power measurements M _PL from the load power measuring section 122A only during the pulse-on period T _on. Here, although it is possible to use an instantaneous value or a representative value of the load power measurement value M _PL as a feedback signal, it is usual to use an average value (preferably a moving average value) of the load power measurement values M _PL as a feedback signal. .

Specifically, it obtains a moving average value AM _PL multiple cycles of the modulation pulse MS for load power measurement M _PL supplied from the load power measuring unit 122A during the pulse-on period T _on, the moving average value Compare the AM _PL and load power set value PL _H sought comparison error or deviation, traveling wave power during the next or subsequent cycle the deviation moderate speed pulse-on period, as close to zero at T _on the A target value of feedback control to be applied to PF, that is, a first control command value _Con is determined. To determine the first control command value C _on, it is possible to use a known algorithm that is commonly used in the feedback control or feed forward control technique.

On the other hand, in each cycle of the modulation pulse MS, the second control command value generation unit 128A takes in the load power measurement value M _PL given from the load power measurement unit 122A only during the pulse off period T _off and uses it as a feedback signal. Use. Again, although it is possible to use an instantaneous value or a representative value of the load power measurement value _MPL as a feedback signal, it is usual to use an average value (preferably a moving average value) of the load power measurement values _MPL as a feedback signal.

Specifically, a moving average value BM _PL for one cycle or a plurality of cycles is acquired for the load power measurement value M _PL given by the load power measurement unit 122A during the pulse off period T _off , and this moving average value Compare the BM _PL with the load power set value PL _L to determine the comparison error or deviation, and in the next or subsequent cycle the power of the traveling wave during the pulse off period T _off so that the deviation approaches zero at a moderate speed A target value of feedback control to be applied to PF, that is, a second control command value C _off is determined. In order to determine this second control command value _Coff , a known algorithm commonly used in feedback control or feedforward control can be used.

As described above, the comparator 130A, a first control instruction at each cycle, during the pulse-on period T _on the traveling wave power detection signal S _PF first control command value generating portion 126A of the modulated pulse MS The comparison error (first comparison error) ER _on is generated in comparison with the value _Con, and during the pulse off period T _off , the traveling wave power detection signal S _PF is output from the second control command value generation unit 128A. A comparison error (second comparison error) ER _off is generated in comparison with the second control command value C _off . The amplifier control unit 132A, in each cycle of the modulation pulses MS, during the pulse-on period T _on is variably controlled by the gain or amplification factor of the power amplifier 92A as close to zero a first comparison error ER _on , during the pulse-off period T _off is variably control the gain or amplification factor of the power amplifier 92A as close to zero a second comparison error ER _off.

Thus, the high frequency power supply 36 for outputting a high-frequency HF by pulse modulation of the high / low, the measured value M _PL of the load power PL obtained from the RF power monitor 96 and the load power measuring unit 122, the pulse-on period T in _on Is matched or approximated to the first load power setting value PL _H , and in the forward direction on the high-frequency feed line 43 so as to match or approximate the second load power setting value PL _L during the pulse off period _Toff. Feedback control is applied to the power PF of the traveling wave that propagates. That is, independent feedback control is applied to the output of the high frequency power supply 36 in the pulse on period _Ton and the pulse off period T _off .

According to the two independent systems of feedback control of the pulse-on period T for _on for a pulse-off period T _off, periodic variation of the synchronization with the modulated pulse MS reflection wave power PR to progressive wave power PF It is possible to easily and appropriately follow up, and can catch up with the sudden load fluctuation that occurs at the time of inversion of the modulation pulse MS without any difficulty. By this, even if the frequency of the modulation pulse MS is increased, the load power PL is kept stable at the individual set values PL _H and PL _L in any of the pulse on period _Ton and the pulse off period T _off. Can.

On the other hand, in the high frequency power source 38 for ion attraction system applying a pulse modulation of the on / off frequency LF is the power control unit 94B, the power PF only traveling wave during the pulse-on period T _on each cycle of the modulation pulses MS On the other hand, feedback control for PL control is applied. The controller 134B in the power supply control unit 94B holds the second control command value generation unit 128B for the pulse off period in a completely paused or inactive state, and generates the first control command value for the pulse on period. Only the generation unit 126B is operated. In this case, for the first control command value generating section 126B, giving a load power set value PL _on to instruct the level of power of the high frequency HF (on level) in the pulse-on period T _on.

The comparator 130B controls the traveling wave power detection signal S _PF from the RF power monitor 96B during the pulse on period T _on in each cycle of the modulation pulse MS and the first control from the first control command value generation unit 126B. compared to the command value C _on generates the comparison error (the first comparison error) ER _on, during the pulse-off period T _off is substantially pause. The amplifier control unit 132B, at each cycle of the modulation pulses MS, during the pulse-on period T _on is variably controlled by the gain or amplification factor of the power amplifier 92B so as to approach zero first comparison error ER _on , Substantially pause during the pulse off period _Toff .

However, it is also possible to perform PF control in the high frequency power supply 38 that performs on / off pulse modulation. In that case, it may be given progressive wave power setting value as a comparison reference value to the comparator 130B from the controller 134B to (PF _S).

[Example of etching process]

The present inventor has experimented the HARC (High Aspect Ratio Contact) process using pulse modulation of the high / low by the plasma etching apparatus shown in FIG. 1, a pulse-off period T _on length, pulse off period T _on the value of the upper DC voltage at a high frequency power (load power) PL _L or pulse-off period T _on is taken as a parameter in, examined the effect of allowing the various process characteristics.

In this experiment, as shown in FIG. 9A, the fine holes 140 are formed in the surface layer portion of the multilayer film structure halfway to the middle (by the depth d ₁ reaching the third SiO ₂ layer 152) by the first etching step. The semiconductor wafer W being prepared was prepared as a sample. Then, with respect to the semiconductor wafer W of this sample, as shown in (b) of FIG. 9, the depth of the fine holes 140 is extended to the lower portion of the third SiO ₂ layer 152 (up to the depth d ₂ ). In the etching process, pulse modulation of high / low is applied to high frequency HF for plasma generation, pulse modulation of on / off is applied to high frequency LF for ion attraction, and DC voltage applied to upper electrode 46 (upper DC voltage An experiment was conducted to vary the magnitude (absolute value) of V _dc in synchronization with the modulation pulse MS. In FIG. 9, 142 is an etching mask (photoresist), 144 is a first SiO ₂ layer, 146 is a first SiN layer, 148 is a second SiO ₂ layer, 150 is a second SiN layer, and 152 is a second 3 is a SiO ₂ layer, 154 is a third SiN layer, and 156 is a semiconductor substrate.

The process characteristics selected for evaluation in this experiment were [1] an increase in the depth of the hole 140 in the second etching step (d ₂ −d ₁ ), ie, an etching amount, and [2] necking near the entrance of the hole 140. (Necking CD), [3] an increase in bowing in the second SiO ₂ layer 152 (intermediate Ox bowing CD), [4] selectivity (increase in depth of hole 140 d ₂ −d ₁ / The decrease in mask thickness d _m ) and the change in [5] aspect ratio (the increase in the depth of the hole 140 d ₂ −d ₁ / intermediate Ox Boeing CD).

More specifically, in the experiment concerning the second etching step, when the power PL _L of the high frequency HF in the pulse off period T _off is set to 0 W and when it is set to 200 W, the pulse off period of various process characteristics is It includes a first experiment to compare the dependencies and a second experiment to compare the upper DC voltage dependencies of various process characteristics. Incidentally, when the power PL _L of a high-frequency HF in the pulse-off period T _off to 0W in pulse modulation of the high / low is the same as applying a pulse modulation on / off.

As main fixed value etching conditions common to the first experiment and the second experiment, the etching gas is C ₄ F ₆ / NF ₃ / Ar / O ₂ = 76/10/75/73 sccm, chamber pressure is 15 mTorr, and the lower electrode temperature 60 ° C., the pulse-on period T _on the 100 [mu] s, pulse-on period T 10000 W power for high-frequency LF attracting ions in _on, the power of the plasma-generating high-frequency HF in the pulse-on period T _on 1000W, pulse the absolute value of the upper DC voltage V _dc in the on-period T _on | V _dc | were as 500V.

<Parameters and results of the first experiment>

In the first experiment to compare the pulse-off period dependent various process characteristics, the absolute value of the upper DC voltage V _dc in the pulse-off period T _off | V _dc | were fixed 900V, the pulse-off period T _off ( T _off = 25 μs (f _S = 8 kHz, D _S = 80%), T _off = 100 μs (f _S = 5 kHz, D _S = 50%), using the frequency f _S and duty ratio D _{S of the} modulation pulse MS as parameters _{, T off = 150μs (f S} = 4kHz, D S = 40%), T off = 233μs (f S = 3kHz, D S = 30%), T off = 400μs (f S = 2kHz, D S = 20% Chose five values of).

10A to 10E graphically show the results obtained in the first experiment. As shown in FIG. 10A, the amount of increase in the depth of the [1] hole 140 (etching amount: d ₂ −d ₁ ) is a pulse off period when the power PL _{L of} high frequency HF is 0 W or 200 W. T _off is in the range of about 700 to 750 nm in the range of 25 μs to 400 μs, and there is no difference. Thus, using high / low pulse modulation with PL _L = 200 W provides an etching amount or etching rate comparable to that using on / off pulse modulation.

As shown in FIG. 10B, in [2] necking CD, when the pulse off period T _off is gradually increased from 25 μs to 400 μs, when the power PL _{L of the} high frequency HF is 0 W, approximately 22.0 to 23.0. whereas stops range, power PL _L of frequency HF stepwise greatly reduced from about 22.0nm for 200W to 18.0nm or less. Thus, using pulse modulation of high / low at PL _L = 200 W (especially when f _S is 3 kH or less and T _off of 233 μs or more), necking is achieved as compared to using on / off pulse modulation. CD is greatly improved.

As shown in FIG. 10C, when the pulse off period T _off is gradually increased from 25 μs to 400 μs as shown in FIG. 10C, when the power PL _{L of the} high frequency HF is 0 W, about 36.0 to 37 whereas stops in the range of 2.0, the power PL _L of frequency HF is greatly reduced from about 37.0nm for 200W to about 34.0Nm (provided that when T _off is equal to or greater than 233Myuesu, not hardly decreased ). Thus, using pulse modulation of high / low at PL _L = 200 W (especially when f _S is 3 kHz or less and T _off of 233 μs or more), it is intermediate compared to using on / off pulse modulation. The Ox Boeing CD will also improve significantly.

As shown in FIG. 10D, [4] selective ratio, if the pulse-off period T _off stepwise increased from 25μs to 233Myuesu, power PL _L of the high frequency HF of about any case in the case of 0W and 200 W 2 It increases at substantially the same rate from about 5 to about 4.2 and saturates when T _off exceeds 233 μs. Thus, using high / low pulse modulation with PL _L = 200 W improves the selection ratio to the same extent as when using on / off pulse modulation.

As shown in FIG. 10E, when the pulse off period T _off is increased stepwise from 25 μs to 400 μs as shown in FIG. 10E, the range of about 80 to 85 when the power PL _{L of the} high frequency HF is 0 W whereas stops, the power PL _L of frequency HF is increased significantly from about 80 in the case of 200W up to about 130 (however, T _off is saturated with more than 233μs). As described above, when using high / low pulse modulation with PL _L = 200 W (especially when f _S is 3 kH or less and T _off is 233 μs or more), the aspect is improved compared to when using on / off pulse modulation. The ratio change rate is greatly improved.

<Parameter and Result of Second Experiment>

In the second experiment to compare the upper DC voltage dependency of various process characteristics, the pulse off period T _off (frequency f _S of the modulation pulse MS, duty ratio D _S ) is T _off = 233 μs (f _S = 3 kHz, D _S Fixed at 30%), and using the absolute value | V _dc | of the upper DC voltage V _dc in the pulse off period T _off as a parameter, select three stepwise values of | V _dc | = 500 V, 900 V and 1200 V It is.

11A to 11E graphically show the results obtained in the second experiment. As shown in FIG. 11A, the amount of increase in the depth of the [1] hole 140 (etching amount: d ₂ −d ₁ ) represents the absolute value | V _dc | of the upper DC voltage V _dc in the pulse off period T _off . 500V, 900V, the stepwise increase 1200 V, the power PL _L of the high frequency HF is linearly decreased to about 680nm to about 760nm in the case of 0 W, if power PL _L of the high frequency HF of 200W from about 700nm to about Gradually decrease to 680 nm. Thus, when using high / low pulse modulation with PL _L = 200 W, the depth of the hole 140 can be obtained even if the absolute value | V _dc | of the upper DC voltage V _dc in the pulse off period T _off is increased. The amount of increase (etching amount) does not necessarily increase, but rather tends to decrease, but is not inferior to the case of using on / off pulse modulation.

As shown in FIG. 11B, [2] necking CD increases the power of high frequency HF when the absolute value | V _dc | of upper DC voltage V _dc in pulse off period T _off is increased stepwise to 500 V, 900 V, and 1200 V. When PL _L is 0 W, it gradually decreases from about 23.0 nm to about 20.0 nm or less, whereas when power PL _L of 200 W is at low frequency, the level is about 19.6 nm to about 17.0 nm. It decreases more gradually to 8 nm. As described above, in the case of using high / low pulse modulation with PL _L = 200 W, the necking CD improves as the absolute value | V _dc | of the upper DC voltage V _dc in the pulse off period T _off increases. Moreover, the necking CD is improved as compared to the case of using on / off pulse modulation.

As shown in FIG. 11C, [3] the intermediate Ox bowing CD increases the absolute value | V _dc | of the upper DC voltage V _dc during the pulse off period T _off to 500 V, 900 V, and 1200 V in a stepwise manner. whereas the power PL _L decreases stepwise from about 37.5nm to about 35.5nm for 0W, the power PL _L of frequency HF is about from about 35.2nm at a lower level in the case of 200W It decreases more gradually to 33.5 nm (although it hardly decreases when | V _dc | becomes 900 V or more). Thus, when using pulse modulation with high / low at PL _L = 200 W, the intermediate Ox Boeing CD is generally increased as the absolute value | V _dc | of the upper DC voltage V _dc in the pulse off period T _off is increased. The intermediate Ox Boeing CD is improved as compared to when using the on / off pulse modulation.

As shown in FIG. 11D, even if the absolute value | V _dc | of the upper DC voltage V _dc in the pulse off period T _off is changed in the range of 500 V to 1200 V as shown in FIG. Both in the case of _L at 0 W and in the case of 200 W fall within the range of about 4.1 to 4.5. Thus, using high / low pulse modulation with PL _L = 200 W improves the selection ratio to the same extent as when using on / off pulse modulation.

As shown in FIG. 11E, when the absolute value | V _dc | of the upper DC voltage V _dc in the pulse off period T _off is gradually increased to 500 V, 900 V, and 1200 V as shown in FIG. Increases from about 80 nm to about 92 nm when | V _dc | becomes 900 V or more when the power PL _L is 0 W, and higher levels when the power PL _{L of the} high frequency HF is 200 W is about 99 nm to about 90 nm It rises more to 132 nm (however, it saturates when | V _dc | becomes 900 V or more). As described above, the use of high / low pulse modulation with PL _L = 200 W greatly improves the aspect ratio change rate as compared to the case of using on / off pulse modulation.

<Evaluation of experiment>

  As described above, in the high aspect ratio contact (HARC) process as shown in FIG. 9, pulse modulation of high / low is applied to pulse modulation of high / low for high frequency HF for generating plasma. It has been found that there is superiority in various process characteristics than in the case, and that bowing can be effectively suppressed while guaranteeing particularly high selectivity. We will consider this point.

  In pulse modulation, when the pulse on period is switched to the pulse off period for each cycle of the modulation pulse, the ion attraction effect is diminished and the plasma reaction product is deposited on the mask. Therefore, it can be said that the low speed pulse / low duty ratio (long pulse-off period) is a region suitable for improving the selection ratio between the mask and the material to be etched or the target film. However, since the pulse off period hardly contributes to the etching, if the pulse off period is made longer than necessary, the time required for the plasma process becomes longer, which leads to a decrease in productivity.

  In addition, when the aspect ratio of hole etching becomes large like HARC, the etching time becomes longer. Therefore, when on / off pulse modulation is used, the hole sidewall can be obtained even if the selection ratio with the mask can be secured. Since long-time ion incidence of the above makes it more likely to cause bowing, it has been difficult to finally obtain a good processed shape.

  Immediately after switching from the pulse on period to the pulse off period, the rates of decrease of electrons, ions and radicals in the processing space of the chamber are different. Electrons are extinguished in a relatively short time of about 10 μs and ions of about 100 μs, whereas radicals exist even after about 1 ms of time has elapsed. It is believed that radicals present during this off-time react with the mask surface layer to form a mask surface protective film.

  In high / low pulse modulation, high frequency HF for plasma generation excites the processing gas even during the pulse-off period to generate ions and radicals. In this case, since the acceleration energy given to the ions is smaller than the high frequency LF for ion attraction, the proportion contributing to the etching is small. On the other hand, considerable radicals are generated, and in the case of the lower two-frequency superposition application method, the power of HF is weak at LF off, so that ions are included at the bottom of the holes by incorporating radicals by a moderate RF bias. Can be drawn into. As a result, deposition of reaction products on the hole sidewalls can be promoted, and a sidewall protective film can be formed to suppress bowing.

  Also, as described above, when high / low pulse modulation is used, various process characteristics are also possible in which the absolute value of the upper DC voltage is increased by one step in the pulse off period than the pulse on period in synchronization with the modulation pulse. In particular, it is effective to improve the necking, to improve the intermediate bowing CD, and to improve the vertical shape.

  That is, by raising the absolute value of the upper DC voltage by one step during the pulse-off period, some action (for example, due to an increase in the energy of electrons injected into the material to be etched and the mask) causes the sidewall in the hole. It is considered that the effect of extending the protective film to the bottom side or the effect of suppressing the shoulder drop of the mask shoulder (thereby reducing the ratio of ion incidence of the oblique component which induces the bowing) can be obtained.

In any case, in the case of applying high / low pulse modulation to the high frequency for plasma generation in the HARC process, the frequency of the modulation pulse is 1 kHz or more (preferably 2 kHz to 8 kHz, more preferably 2 kHz to 3 kHz) It is desirable to set the power PL _L of the plasma generating high frequency power HF in the pulse-off period to a somewhat high range (for example, 100 W or more, preferably 200 W or more).

In this point, in the plasma etching apparatus according to this embodiment, the plasma generating system matching unit 40 is a plasma load visible on the high frequency power supply line 43 by the high frequency power supply 36 by the impedance sensor 106A having the above configuration and function. the impedance was measured to obtain the weighted average measurement value obtained by the measurement value of the load impedance at the measurement and pulse-off period T _on of the load impedance in the pulse-on period T _on weighted by a desired weighting, this It operates to match the weighted average measurement to the output impedance of the high frequency power supply 36. In this case, by adjusting the value of the weighted average of the weight variable (K), the pulse-on period T _on any of the balance between the reflected wave power PR _H in the reflected wave power PR _H and the pulse-off period T _off in Since control can be performed, it is possible to arbitrarily reduce the power PR _L of the reflected wave in the pulse off period T _off and to set the load power PL _L to a higher value arbitrarily.

As an example, in a high-frequency power source (1200 W is permissible limit value of the reflected wave power) of the actual certain models used in the high frequency power supply 36 of the plasma generation system, as shown in FIG. 12, the pulse-on period T _on compared with the case of performing conventional matching method the reflection coefficient .GAMMA is .GAMMA = 0.0 (how to take a substantially full alignment during the pulse-on period T _on) in, Г = 0.2, Г = 0 The settable range of the load power PL _L in the pulse off period T _off is about 230 W (Г = 0.0) to about 300 W (Г = 0.2) by using the matching method according to the embodiment which is .3. Furthermore, it can be greatly expanded to about 350 W (Г = 0.3). This means that, from another point of view, downsizing of the high frequency power supply 36 is possible. The reflection coefficient Г is given by Г = (PR _H / PF _H ) ^1/2 .

[Example concerning measures against upper electrode discharge]

  In general, in hole etching such as the HARC process, when the aspect ratio is increased, positive ions are likely to be accumulated at the bottom of the hole, and the rectilinearity of the ions in the hole is reduced to obtain a good etching shape. It will be difficult. In this regard, the plasma etching apparatus of FIG. 1 includes the DC power supply unit 62, and applying a negative DC voltage to the upper electrode 46 causes electrons emitted from the upper electrode 46 to the plasma generation space PA to be generated. The semiconductor wafer W is accelerated toward the semiconductor wafer (object to be processed) W on the susceptor (lower electrode) 16, and the accelerated electrons are supplied to the inner part of the hole, and positive ions accumulated at the bottom of the hole are electrically Since it is possible to sum up, it is possible to avoid the problem that the straightness of ions decreases in the holes as described above.

  However, by applying a DC voltage of negative polarity to the upper electrode 46, gas discharge (abnormal discharge) is generated in the upper electrode 46, particularly in the gas injection holes 48a to the gas vents 50a, and the upper electrode 46 is generated. Can be damaged. Such abnormal discharge inside the upper electrode is likely to occur frequently when on / off pulse modulation is applied to both the high frequency HF for plasma generation and the high frequency LF for ion attraction.

In this case, as shown in FIG. 13, during the pulse off period T _off , both the high frequency power supply 38 for ion attraction and the high frequency power supply 36 for plasma generation are turned off, while the DC power supply is used for the upper electrode 46. A negative DC voltage V _dc1 having a large absolute value is applied from the portion 62. Thereby, in the vicinity of the surface of the upper electrode 46, a high electric field region (hereinafter referred to as "DC sheath") SH _DC is generated which accelerates in the direction of pushing electrons (e) and accelerates ions (+). The electrons (e) accelerated by the DC sheath SH _DC enter the semiconductor wafer W on the susceptor 16 to neutralize the positive charge accumulated at the bottom of the hole. At this time, since the plasma generating space PA is extinguished plasma, the plasma sheath (ion sheath) SH _RF over the surface of the semiconductor wafer W is not formed almost. This state is maintained throughout the pulse off period _Toff .

When the changes from the pulse-off period T _off the pulse-on period T _on, both of the two high-frequency power source 36 is turned ON at the same time, both high frequency HF, LF is applied to the susceptor 16. This will produce the plasma of a processing gas into the plasma generation space PA, the plasma sheath SH _RF is formed in the chamber 10 so as to cover the surface of the semiconductor wafer W. In this case, the plasma sheath SH _RF suddenly appears from the substantially absence state so far and grows rapidly toward the upper electrode 46 (the thickness of the sheath increases). The plasma sheath SH _RF growth rate is mainly dependent on the magnitude of the rising speed or the saturation value of the voltage (peak-to-peak value) V _pp of the high-frequency LF for attracting low frequencies relatively ions.

On the other hand, in the upper electrode 46, although the absolute value of the DC voltage applied by the DC power supply 62 changes from the relatively large value | _Vdc1 | to the relatively small value | _Vdc2 |, the electrons (e) Are discharged and accelerated toward the semiconductor wafer W. However, unlike the case of pulse-off period T _off, since the plasma sheath SH _RF on the semiconductor wafer W in this situation grows at a rapid degree in the direction in which the thickness, i.e. the electric field intensity increases, accelerating from the upper electrode 46 side The electrons (e) that have been made are strongly repelled by the growing plasma sheath SH _RF . The plasma sheath SH _RF at repelled electrons (e) is in turn flying toward the upper electrode 46, the DC sheath SH _DC gas ejection holes 48a of the electrode plate 48 of the upper electrode 46 against the electric field It may enter inside and cause discharge inside it.

As described above, when abnormal discharge occurs in the upper electrode, the electrons (e) emitted from the upper electrode 46 are accelerated toward the semiconductor wafer W side, and the plasma sheath SH _RF on the semiconductor wafer W side is used. When decelerating the bounced electrons (e), the force of the electric field of the DC sheath SH _DC on the upper electrode 46 side acting on the electrons (e) is the same. Therefore, the frequency and speed at which the electrons enter the gas ejection holes 48a of the upper electrode 46 are almost independent of the size of the DC sheath SH _DC , and the plasma sheath SH _RF has electrons (e) on the upper electrode 46 side. It depends on the strength to bounce back, that is, the growth rate of the plasma sheath SH _RF .

Also, even if positive ions (+) generated in the upper part of the plasma generation space PA are drawn into the electric field of the DC sheath SH _DC and collide with the surface of the upper electrode 46 (electrode plate 48) and sputtered. There is nothing to cause abnormal discharge inside the upper electrode 46.

  In the plasma etching apparatus of FIG. 1, the above-mentioned abnormal discharge inside the upper electrode 46 is effective by changing the pulse modulation for high frequency HF for plasma generation from on / off pulse modulation to high / low pulse modulation. Can be avoided.

In this case, as shown in FIG. 14, during the pulse-off period _Toff , the high frequency power supply 36 is kept on and the high frequency power HF for plasma generation is applied to the susceptor 16 with low level power. the generating space PA remains at a low density without extinction plasma, the surface of the semiconductor wafer W is covered with a thin plasma sheath SH _RF. At this time, electrons (e) accelerated to a high speed from the upper electrode 46 side by the large electric field of the DC sheath SH _DC receive a reverse electric field or force in the plasma sheath SH _RF . However, since the plasma sheath SH _RF thin field of the opposite direction is weak, electron (e) is incident on the semiconductor wafer W penetrates the plasma sheath SH _RF. This state is maintained throughout the pulse off period _Toff .

When the changes from the pulse-off period T _off the pulse-on period T _on, along with the high frequency power source 38 is turned on to apply a high-frequency LF for ion attraction to the susceptor 16, the high frequency power supply 36 is a power of the high frequency HF which Change from low level to high level. Thus, the density of the plasma generated in the plasma generating space PA is rapidly increased, the thickness of the plasma sheath SH _RF covering the surface of the semiconductor wafer W is increased further. However, in this case, the growth rate is fairly moderate because the plasma sheath SH _RF does not suddenly appear and suddenly grow from an empty state, but merely increases the thickness from an existing state. The force to repel electrons (e) accelerated at high speed from the electrode 46 side is not so large. Thus, the plasma sheath SH _RF at repelled electrons (e), since the initial rate of the bounce is low, can not penetrate the DC sheath SH _DC, the electrode plate 48 of the upper electrode 46 of the gas ejection holes 48a Do not enter inside. Therefore, abnormal discharge does not occur inside the upper electrode 46.

Meanwhile, when the abnormal discharge inside the upper electrode 46 during the pulse-on period T _on is generated, the peak-to-peak value V _pp for ion attraction high frequency LF related to the growth rate and thickness of the plasma sheath SH _RF is A large fluctuation on the high frequency feed line 45 has been confirmed. In the plasma etching apparatus of this embodiment, the V _pp detectors 107A and 107B are respectively provided in the matching units 40 and 42 (FIG. 3). Through V _pp detector 107B in the matching unit 42, to measure the peak-to-peak value V _pp for ion attraction high frequency LF on high frequency power supply line 45, the V _pp by CPU processing of the main control unit 72 or the matching controller 104B The measurement values can be analyzed to obtain monitor information (FIGS. 15 and 16) indicating whether or not an abnormal discharge occurs inside the upper electrode 46.

Here, the monitor information of FIG. 15 is an example (one example) obtained when the abnormal discharge is generated inside the upper electrode 46. As shown in the drawing, it can be seen that the V _pp fluctuation rate jumps up frequently (more than several percent) in the determination section set in the monitoring period. In general, as the frequency of occurrence of abnormal discharge increases, the V _pp fluctuation rate tends to increase. The V _pp variation rate on the vertical axis of the illustrated graph is given, for example, by the following equation (2).
V _pp fluctuation rate = 100 × (V _pp-max- V _pp-ave ) / V _pp-ave (2)
However, V _pp-max is the maximum value of V _pp in a certain sampling period T _S set in the judgment section, and V _pp-ave is an average value of V _pp in the sampling period T _S.

The monitor information in FIG. 16 is an example (one example) obtained when the abnormal discharge does not occur inside the upper electrode 46. The V _pp fluctuation rate is stable at several percent or less (1% or less in the illustrated example) throughout the determination section. Immediately after and immediately before the end of the monitoring period is the timing of ignition and extinction of plasma, and since the V _pp fluctuation rate rises regardless of the occurrence of abnormal discharge, it is excluded from the judgment section.

The inventors conducted an experiment in which the gas pressure, the frequency f _{s of} pulse modulation and the duty ratio D _s were selected as parameters in the HARC process as described above, and the abnormal discharge inside the upper electrode in each pulse modulation was performed. Were examined for the occurrence of In this experiment, using a fluorocarbon-based gas in the same manner as the etching gas and the above-described embodiment, the pulse-on period T 2000 kW power plasma-generating high-frequency HF in _on, 14000KW the power of ion attraction high frequency LF, pulses The power of the high frequency HF in the off period T _off is 100 W. The gas pressure is selected as five parameters of 10 mTorr, 15 mTorr, 20 mTorr, 25 mTorr, and 30 mTorr as parameters, the pulse modulation frequency f _s is selected as 4 kHz, 5 kHz, and 10 kHz, and the duty ratio D _s is 20%, 30 We chose five ways:%, 40%, 50%, and 60%.

The experimental results are shown in tabular form in FIGS. 17A and 17B. In the table, 〇 represents the case where the V _pp fluctuation rate falls below 2% (permissible value) in the above monitor information, and represents the determination result of “abnormal discharge not occurring”. The symbol “×” represents the case where the V _pp fluctuation rate exceeds 2% (permissible value) in the monitor information, and indicates the determination result of “abnormal discharge present”.

FIG. 17A shows the case where on / off pulse modulation is applied to high frequency HF for plasma generation and both. In this case, the results of “abnormal discharge present” (×) are widely distributed over the entire variable range of all parameters (gas pressure, pulse modulation frequency f _s , duty ratio D _s ).

FIG. 17B shows the case where high / low pulse modulation is applied to high frequency HF for plasma generation, and on / off pulse modulation is applied to high frequency LF for ion attraction. In this case, it was all parameters (gas pressure, pulse modulation frequency f _s, D _s duty ratio) "no abnormal discharge" always over the entire variable region of (〇).

As described above, by selecting the modulation mode in which high / low pulse modulation is applied to high frequency HF for plasma generation and on / off pulse modulation is applied to high frequency LF for ion attraction, the inside of upper electrode 46 is selected. Abnormal discharge can be effectively avoided. However, this technique is suitably requires a technique that can be held accurately and stably the plasma generating high frequency HF of the power (the load power) to a lower optimum setting value during the pulse-off period T _off. In this regard, as described above, the reflected wave in the reflection wave power PR _H and the pulse-off period T _off in the pulse-on period T _on by adjusting the value of the weighting factor K in the impedance sensor 106A of the matching device 40 A technique for arbitrarily controlling the balance with the power PR _L and a technique for applying independent feedback control to the load power PL _L during the pulse off period T _off in the high frequency power supply 36 can be suitably used.

[Other Embodiments or Modifications]

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the technical idea thereof.

  In the present invention, when combining the first (plasma generation system) power modulation system, the second (ion pull-in system) power modulation system, and the upper DC application system, it is possible to select each mode arbitrarily. In addition, high frequency LF for plasma generation is subjected to high / low pulse modulation without applying pulse modulation to the power of high frequency LF for ion attraction, or conversely, pulse modulation is applied to high frequency HF for plasma generation. A mode is also possible in which high / low pulse modulation is applied to the power of the high frequency LF for ion attraction without any application. Furthermore, a form using only either the first power modulation method or the second power modulation method or a form not using the upper DC application method is also possible.

  In the above embodiment (FIG. 1), high frequency HF for plasma generation is applied to the susceptor (lower electrode) 16. However, a configuration in which high frequency HF for plasma generation is applied to the upper electrode 46 is also possible.

  The present invention is not limited to a capacitively coupled plasma etching apparatus, and is applicable to a capacitively coupled plasma processing apparatus that performs any plasma process such as plasma CVD, plasma ALD, plasma oxidation, plasma nitriding, sputtering, etc., and further, a chamber The present invention is also applicable to an inductively coupled plasma processing apparatus in which a high frequency electrode (antenna) is provided around the. The object to be treated in the present invention is not limited to a semiconductor wafer, and various substrates for flat panel displays, organic ELs, solar cells, photomasks, CD substrates, printed substrates and the like are also possible.

10 chamber 16 susceptor (lower electrode)
36 (plasma generation system) high frequency power supply 38 (ion drawing system) high frequency power supply 40, 42 matching unit 43, 45 high frequency power supply line 46 upper electrode (shower head)
56 Processing Gas Supply Source 72 Main Control Unit 90A, 90B High Frequency Oscillator 92A, 92B Power Amplifier 94A, 94B Power Control Unit 96A, 96B RF Power Monitor 98A, 98B Matching Circuit 100A, 102A, 100B, 102B Motor 104A, 104B Matching Controller 107A , 107B V _pp detector 110A, 110B RF voltage detector 112A, 112B RF current detector 114A, 114B load impedance instantaneous value calculation circuit 116A, 116B arithmetic average value calculation circuit 118A, 118B weighted average value calculation circuit 120A, 120B moving average Value calculation circuit 122A, 122B load power measurement unit 124A, 124B high frequency output control unit 126A, 126B (for pulse on period) control command value generation unit 128A, 128B Vinegar for off period) control command value generating unit
130A, 130B comparator 132A, 132B amplifier control circuit 134A, 134B controller 136A, 136B switching circuit

Claims (11)

Plasma processing is performed to generate plasma by high frequency discharge of processing gas in a vacuum-evacuable processing container that accommodates objects to be processed in and out so as to perform desired processing on the object in the processing container under the plasma. A device,
A first high frequency power supply outputting a first high frequency;
In the first and second periods alternately repeating at a fixed duty ratio, the power of the first high frequency becomes high level in the first period, and the power of the first high frequency is in the second period A first high frequency power modulation unit that modulates the output of the first high frequency power supply with a modulation pulse of a constant frequency so as to be a low level lower than the high level;
A first high frequency feed line for transmitting the first high frequency output from the first high frequency power source to a first electrode disposed in or around the processing container;
The impedance of the load visible from the first high frequency power supply is measured on the first high frequency power feed line, and the measured value of the load impedance in the first period and the measured value of the load impedance in the second period are desired A first matching unit for matching a weighted average measurement value obtained by weighted averaging with the weight of the first high frequency power source with the output impedance of the first high frequency power supply. A second high frequency power supply that outputs a second high frequency;
A second high frequency power supply line for transmitting the second high frequency power output from the second high frequency power supply to a second electrode disposed in or around the first electrode or the processing container;
In the first period, the power of the second high frequency is turned on or high level, and in the second period, the power of the second high frequency is turned off or low level lower than the high level, The plasma processing apparatus according to claim 1, further comprising: a second high frequency power modulation unit that modulates an output of the second high frequency power supply with the modulation pulse.   The plasma processing apparatus according to claim 2, wherein the second high frequency has a frequency suitable for drawing ions from the plasma into the object. The first high frequency power supply
Power of a traveling wave propagating forward from the first high frequency power source to the first electrode on the first high frequency power supply line and from the first electrode to the first high frequency power source A first RF power monitor that detects the power of a reflected wave propagating in the reverse direction and generates a traveling wave power detection signal and a reflected wave power detection signal respectively representing the power of the traveling wave and the power of the reflected wave;
A first load power measurement unit for obtaining a measured value of load power supplied to a load including the plasma from the traveling wave power detection signal obtained from the RF power monitor and the reflected wave power detection signal;
During the second period in each cycle of the modulation pulse, the power of the traveling wave is made to match or approximate the measured value of the load power obtained from the load power measurement unit to a predetermined load power setting value. The plasma processing apparatus according to any one of claims 1 to 3, further comprising: a first high-frequency output control unit that applies feedback control to the control unit. The first high frequency power supply
Power of a traveling wave propagating forward from the first high frequency power source to the first electrode on the first high frequency power supply line and from the first electrode to the first high frequency power source A first RF power monitor that detects the power of a reflected wave propagating in the reverse direction and generates a traveling wave power detection signal and a reflected wave power detection signal respectively representing the power of the traveling wave and the power of the reflected wave;
A first load power measurement unit for obtaining a measured value of load power supplied to a load including the plasma from the traveling wave power detection signal obtained from the RF power monitor and the reflected wave power detection signal;
During the first and second periods of each cycle of the modulation pulse, first and second measurement values of the load power obtained from the load power measurement unit are given separately for the first and second periods. A first high-frequency output control unit for performing feedback control individually on the power of the traveling wave in the first period and the second period so as to match or approximate the load power setting value of 2, respectively; The plasma processing apparatus as described in any one of Claims 1-3 which has these.   The plasma processing apparatus according to any one of claims 1 to 5, wherein the first high frequency wave has a frequency suitable for generating the plasma.   The plasma processing apparatus according to claim 6, wherein the object to be processed is placed on the first electrode.   The plasma processing apparatus according to any one of claims 1 to 7, wherein the power of the second high frequency in the second period is higher than the minimum power required to maintain the plasma generation state.   The plasma according to any one of claims 1 to 8, further comprising: a DC power supply unit that applies a negative DC voltage to the second electrode only during the second period in synchronization with the modulation pulse. Processing unit.   A DC voltage of negative polarity is applied to the electrode facing the object in the processing vessel via the plasma generation space, and during the second period rather than during the first period in synchronization with the modulation pulse The plasma processing apparatus according to any one of claims 1 to 9, further comprising: a DC power supply unit that increases the absolute value of the DC voltage at the time of.   The plasma processing apparatus according to any one of claims 1 to 10, wherein a frequency of the modulation pulse is 2 to 8 kHz, and a duty ratio is 20 to 80%.