JP4831853B2 - Capacitively coupled parallel plate plasma etching apparatus and plasma etching method using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a capacitively coupled parallel plate plasma etching apparatus for performing plasma etching processing on a substrate such as a semiconductor substrate and a plasma etching method using the same .
[0002]
[Prior art]
For example, in a semiconductor device manufacturing process, a plasma etching process is employed to form a circuit on a semiconductor wafer that is a substrate to be processed. Various apparatuses are used as the plasma etching process. Among them, a capacitively coupled parallel plate plasma etching apparatus is the mainstream.
[0003]
In the capacitively coupled parallel plate plasma etching apparatus, a pair of parallel plate electrodes (upper and lower electrodes) are disposed in a chamber, a processing gas is introduced into the chamber, and a high frequency is applied to one of the electrodes to provide a gap between the electrodes. A high frequency electric field is formed, plasma of a processing gas is formed by the high frequency electric field, and a plasma etching process is performed on the semiconductor wafer.
[0004]
When etching a film on a semiconductor wafer, such as an oxide film, using such a capacitively coupled parallel plate plasma etching apparatus, optimum radical control is possible by forming a medium density plasma with a medium pressure inside the chamber. Thus, an appropriate plasma state can be obtained, and etching with high stability and reproducibility is realized with a high selection ratio.
[0005]
However, in recent years, design rules in USLI have been further miniaturized, and a higher hole shape aspect ratio has been demanded, and conventional conditions for oxide film etching and the like are not necessarily sufficient.
[0006]
Thus, attempts have been made to form high-density plasma while increasing the frequency of the applied high-frequency power and maintaining a good plasma dissociation state. This makes it possible to form an appropriate plasma under a lower pressure condition, and is considered to be able to appropriately cope with further miniaturization of design rules.
[0007]
[Problems to be solved by the invention]
By the way, according to the examination results of the present inventors, when the plasma is densified in this way, the non-linear characteristic of the plasma appears remarkably, the harmonics of the reflected wave from the plasma increase, and the electrode diameter is φ250 to φ300. In this case, it has been found that a standing wave is generated on the electrode surface by such a harmonic, and the electric field distribution on the electrode surface becomes non-uniform.
[0008]
If the electric field distribution becomes non-uniform in this way, the plasma density becomes non-uniform, resulting in non-uniform etching rate distribution. Therefore, it is necessary to remove the cause of the non-uniform electric field distribution and make the etching rate distribution uniform. Become.
[0009]
However, in the past, the problems in the case of using such high-density plasma have not always been clearly recognized, and no attempt has been made yet to solve the above-described non-uniform electric field distribution. .
[0010]
The present invention has been made in view of such circumstances, and in plasma etching processing using high-density plasma that can cope with further miniaturization, the plasma density is made uniform by reducing non-uniformity of the electric field distribution on the electrode surface. An object of the present invention is to provide a capacitively coupled parallel plate plasma etching apparatus and a plasma etching method in which the etching rate distribution is uniform.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention includes a chamber in which a substrate to be processed is accommodated,
An upper electrode and a lower electrode provided in parallel to face each other in the chamber;
High frequency applying means for applying a high frequency of 27 MHz or higher to the upper electrode;
DC voltage application means for applying a DC voltage to the upper electrode;
High frequency applying means for applying a high frequency of 100 kHz to 10 MHz to the lower electrode;
An exhaust means for maintaining the inside of the chamber at a predetermined reduced pressure state;
A processing gas introduction means for introducing a processing gas into the chamber;
A plasma of a processing gas is formed by forming a high-frequency electric field between the upper electrode and the lower electrode while the substrate to be processed is supported on the lower electrode, and a direct current from the DC voltage applying means is formed on the upper electrode. A capacitively coupled parallel plate plasma etching apparatus is provided in which a self-bias voltage on the surface of the upper electrode is increased by applying a voltage, and a plasma etching process is performed on the substrate to be processed by the plasma.
[0015]
The present invention further includes a chamber that accommodates a substrate to be processed;
An upper electrode and a lower electrode provided in parallel to face each other in the chamber;
High frequency applying means for applying a high frequency of 27 MHz or higher to the upper electrode;
High frequency applying means for applying a high frequency of 100 kHz to 10 MHz to the lower electrode;
DC voltage application means for applying a DC voltage to the upper electrode;
An exhaust means for maintaining the inside of the chamber at a predetermined reduced pressure state;
A plasma etching method for performing plasma etching using a capacitively coupled parallel plate plasma etching apparatus provided with a processing gas introducing means for introducing a processing gas into the chamber,
A plasma of a processing gas is formed by forming a high frequency electric field between the upper electrode and the lower electrode while the substrate to be processed is supported on the lower electrode, and a direct current from the DC voltage applying means is applied to the upper electrode. A plasma etching method is provided in which a voltage is applied to increase a self-bias voltage on the surface of the upper electrode, and a plasma etching process is performed on a substrate to be processed.
[0017]
As described above, the harmonics from the plasma form a standing wave in the plane of the upper electrode (first electrode), so that the electric field distribution on the upper electrode surface becomes non-uniform. As a result, the plasma sheath of the upper electrode becomes thinner at the center of the electrode, and the self-bias voltage on the electrode surface becomes non-uniform. In other words, since the standing wave has a larger amplitude at the center of the electrode, the standing wave affects the electric field distribution of the upper electrode and contributes to the plasma near the upper electrode. Thinner than At this time, if the frequency applied to the upper electrode is relatively low, that is, less than 27 MHz, the self-bias voltage (V _dc ) is large and the plasma sheath is thick, so that the standing wave has an effect on the plasma uniformity. Is small. Further, since the wavelength of the high frequency is large and the wavelength of the harmonic is also large, a standing wave that affects the plasma processing is hardly generated.
However, when the frequency of the high frequency applied to the upper electrode is increased to 27 MHz or higher, the self-bias voltage (V _dc ) on the electrode surface also decreases, and as a result, the entire thickness of the plasma sheath decreases, so that the self wave is generated by the standing wave When the plasma sheath at the center of the electrode is further thinned due to the nonuniformity of the bias voltage (V _dc ), the rate of change of the plasma sheath thickness is increased, and the uniformity of the plasma is deteriorated.
In contrast, in the present invention, a high frequency of 27 MHz or higher is applied to the first electrode, and a DC voltage is further applied to the first electrode, so that the self-bias voltage (V _dc ) increases, the plasma sheath becomes thicker, and the degree of nonuniformity of the plasma sheath due to nonuniformity of the self-bias voltage ( _Vdc ) can be reduced. Therefore, the plasma density can be made uniform and the etching rate distribution can be made uniform .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a sectional view schematically showing an etching processing apparatus according to the first embodiment of the present invention. This etching processing apparatus 1 is configured as a capacitive parallel plate etching apparatus in which electrode plates face each other in parallel in the vertical direction, and a plasma forming power source is connected to one of them.
[0019]
The plasma etching apparatus 1 has a chamber 2 formed into a cylindrical shape made of aluminum, for example, whose surface is anodized (anodized), and the chamber 2 is grounded. A substantially cylindrical susceptor support 4 for placing an object to be processed, for example, a semiconductor wafer (hereinafter referred to as “wafer”) W, is provided at the bottom of the chamber 2 via an insulating plate 3 such as ceramic. Further, a susceptor 5 constituting a lower electrode is provided on the susceptor support 4. The susceptor 5 is connected to a high pass filter (HPF) 6 for passing a high frequency of 60 MHz described later.
[0020]
A refrigerant chamber 7 is provided inside the susceptor support 4, and a refrigerant such as liquid nitrogen is introduced into the refrigerant chamber 7 through a refrigerant introduction pipe 8 and circulated, and the cold heat is Heat is transferred to the wafer W via the susceptor 5, whereby the processing surface of the wafer W is controlled to a desired temperature.
[0021]
The susceptor 5 is formed in a disc shape having a convex upper center portion, and an electrostatic chuck 11 having substantially the same shape as the wafer W is provided thereon. In the electrostatic chuck 11, an electrode 12 is interposed between insulating materials, and a DC voltage of, for example, 1.5 kV is applied from a DC power source 13 connected to the electrode 12. Electrostatic adsorption.
[0022]
The insulating plate 3, the susceptor support 4, the susceptor 5 and the electrostatic chuck 11 are supplied with a gas for supplying a heat transfer medium, for example, He gas, to the back surface of the wafer W, which is an object to be processed. A passage 14 is formed, and the cold heat of the susceptor 5 is transmitted to the wafer W through the heat transfer medium so that the wafer W is maintained at a predetermined temperature.
[0023]
An annular focus ring 15 is disposed at the upper peripheral edge of the susceptor 5 so as to surround the wafer W placed on the electrostatic chuck 11. The focus ring 15 is made of a conductive material such as silicon, which improves the etching uniformity.
[0024]
An upper electrode 21 is provided above the susceptor 5 so as to face the susceptor 5 in parallel. The upper electrode 21 is supported on the upper portion of the chamber 2 via an insulating material 25, constitutes an opposing surface to the susceptor 5, and has an electrode plate 23 having a number of discharge holes 24, and the electrode plate 23. The electrode support 22 has a water-cooling structure made of a conductive material, for example, aluminum whose surface is anodized. In addition, the susceptor 5 which is a lower electrode and the upper electrode 21 are separated from each other by about 10 to 60 mm, for example.
[0025]
A gas inlet 26 is provided in the electrode support 22 in the upper electrode 21, and a gas supply pipe 27 is connected to the gas inlet 26. Further, the gas supply pipe 27 includes a valve 28, and A processing gas supply source 30 is connected via the mass flow controller 29. A processing gas for etching is supplied from the processing gas supply source 30.
[0026]
Various conventionally used gases can be employed as the processing gas, for example, a gas containing a halogen element such as a fluorocarbon gas (C _x F _y ) or a hydrofluorocarbon gas (C _p H _q F _r ). Can be suitably used. In addition, a rare gas such as Ar or He or N ₂ may be added.
[0027]
An exhaust pipe 31 is connected to the bottom of the chamber 2, and an exhaust device 35 is connected to the exhaust pipe 31. The exhaust device 35 includes a vacuum pump such as a turbo molecular pump, and is configured so that the inside of the chamber 2 can be evacuated to a predetermined reduced pressure atmosphere, for example, a predetermined pressure of 1 Pa or less. Further, a gate valve 32 is provided on the side wall of the chamber 2, and the wafer W is transported between adjacent load lock chambers (not shown) with the gate valve 32 opened. ing.
[0028]
The upper electrode 21 is connected to a high-frequency power source 40 for plasma formation via a matching unit 41. The high-frequency power source 40 has a high frequency of 27 MHz or more, and by applying such a high frequency, a high-density plasma can be formed in a preferable dissociated state in the chamber 2 under low pressure conditions. Plasma processing becomes possible. In this example, a high frequency power supply 40 of 60 MHz is used. The upper electrode 21 is connected to a DC power source 43 for increasing the self-bias voltage (V _dc ) of the upper electrode 21 through a low-pass filter (LPF) 44 that passes only DC. In addition, since a capacitor (not shown) is provided in series in the matching unit 41, the high frequency power supply 40 and the DC power supply 43 do not collide.
[0029]
A susceptor 5 as a lower electrode is connected to a high frequency power supply 50 for ion attraction, and a matching unit 51 is interposed in the power supply line. The second high-frequency power supply 50 has a frequency in the range of 100 kHz to 10 MHz. By applying a frequency in such a range, the second high-frequency power supply 50 is appropriate without damaging the wafer W that is the object to be processed. An ionic effect can be provided. In this example, a 2 MHz one is used.
[0030]
Next, the processing operation in the plasma etching apparatus 1 configured as described above will be described.
First, after the gate valve 32 is opened, the wafer W that is an object to be processed is loaded into the chamber 2 from a load lock chamber (not shown) and placed on the electrostatic chuck 11. The wafer W is electrostatically adsorbed on the electrostatic chuck 11 by applying a DC voltage from the high-voltage DC power supply 13. Next, the gate valve 32 is closed, and the inside of the chamber 2 is evacuated to a predetermined degree of vacuum by the exhaust device 35.
[0031]
Thereafter, the valve 28 is opened, and the processing gas from the processing gas supply source 30 is introduced into the upper electrode 21 through the processing gas supply pipe 27 and the gas inlet 26 while its flow rate is adjusted by the mass flow controller 29. Further, as shown by an arrow in FIG. 1 through the discharge hole 24 of the electrode plate 23, the wafer W is uniformly discharged, and the pressure in the chamber 2 is maintained at a predetermined value.
[0032]
Thereafter, a high frequency of 27 MHz or higher, for example, 60 MHz, is applied to the upper electrode 21 from the high frequency power supply 40. As a result, a high-frequency electric field is generated between the upper electrode 21 and the susceptor 5 as the lower electrode, the processing gas is dissociated into plasma, and the wafer W is etched by this plasma.
[0033]
On the other hand, a high frequency of 100 kHz to 10 MHz, for example, 2 MHz is applied from the high frequency power supply 50 to the susceptor 5 that is the lower electrode. Thereby, ions in the plasma are drawn to the susceptor 5 side, and the anisotropy of etching is enhanced by ion assist.
[0034]
Thus, the plasma density can be increased by setting the frequency of the high frequency applied to the upper electrode 21 to 27 MHz or more. However, with this alone, the standing wave is generated on the lower surface of the electrode plate 23 by the harmonics of the reflected wave from the plasma. Is generated, the non-uniformity of the electric field on the lower surface of the electrode plate 23 occurs.
[0035]
That is, in the case of only the high frequency power supply 40, the harmonics from the plasma form a standing wave on the surface of the upper electrode 21, so that the electric field distribution on the upper electrode surface becomes non-uniform. When the frequency of the high frequency applied to the upper electrode is increased to 27 MHz or higher, the self-bias voltage (V _dc ) on the electrode surface also decreases, and as a result, as shown in FIG. Since the overall thickness of the electrode sheath is reduced, the plasma sheath at the center of the electrode is further thinned due to the non-uniformity of the electric field distribution due to standing waves, so that the rate of change in the plasma sheath thickness increases and the electrode surface The self-bias voltage is non-uniform. As a result, the plasma uniformity deteriorates.
[0036]
On the other hand, as described above, a high frequency with a frequency higher than 27 MHz is applied to the upper electrode 21 from the high frequency power source 40 and a direct current voltage is applied from the direct current power source 43, thereby FIG. As shown in the _{figure, the} self-bias voltage (V _dc ) increases by the DC voltage, and the contribution S ₁ forms a thicker plasma sheath S ′, resulting in non-uniform self-bias voltage (V _dc ) and plasma. The degree of non-uniformity of the sheath can also be reduced. Therefore, the plasma density can be made uniform and the etching rate distribution can be made uniform.
[0037]
For example, when high frequency power of 60 MHz and 1 kW is applied from the high frequency power supply 40 to the electrode 21, V _dc = about −100 V, and when the variation of V _dc is about ± 10 V, the variation ratio is ± 10. %, The uniformity of the plasma is lowered.
[0038]
However, when −400 V, for example, is applied from the DC power supply 43, the overall V _dc is − (100 + 400) V ± 10 V, and the variation rate of V _dc is ± 2%, improving the uniformity of V _dc. . As a result, plasma uniformity is also improved.
[0039]
Next, a second embodiment of the present invention will be described. FIG. 3 is a cross-sectional view schematically showing a plasma etching apparatus according to the second embodiment of the present invention. As in the first embodiment, this plasma etching apparatus 1 ′ is also configured as a capacitive parallel plate etching apparatus in which the electrode plates face each other in parallel in the vertical direction and a plasma forming power source is connected to one of them, as shown in FIG. 1 that are basically the same as those in FIG.
[0040]
In the present embodiment, unlike the first embodiment, two high-frequency power sources are connected to the upper electrode 21. That is, a first high-frequency power source 60 for plasma formation is connected through a high-pass filter (HPF) 62 and a matching unit 61, and a second high-frequency power source 63 is connected through a low-pass filter 65 and a matching unit 64.
[0041]
The first high-frequency power source 60 has a high frequency of 27 MHz or higher. By applying such a high frequency, a high-density plasma can be formed in a preferable dissociated state in the chamber 2, and a low-pressure Plasma processing under conditions is possible. In this example, 60 MHz is used as the first high frequency power supply 60.
[0042]
The second high-frequency power source 63 has a frequency lower than that of the first high-frequency power source 60 and is preferably 2 to 10 MHz. In this example, a 2 MHz power source is used. Since the second high frequency power supply 63 has a frequency lower than that of the first high frequency power supply 60 as described above, it has a function of increasing the self-bias voltage (V _dc ) of the upper electrode 21.
[0043]
The high-pass filter (HPF) 62 is for cutting frequencies below the frequency of the second high-frequency power source 63, and the low-pass filter (LPF) 65 is for cutting frequencies above the frequency of the first high-frequency power source 60. Is.
[0044]
In the plasma etching apparatus 1 ′ configured as described above, the etching process is basically performed in the same manner as the plasma etching apparatus 1 according to the first embodiment. In this case, as in the first embodiment, the plasma density can be increased by setting the frequency of the high frequency applied to the upper electrode 21 to 27 MHz or more. However, this is only caused by harmonics of reflected waves from the plasma. Generation of a standing wave on the lower surface of the electrode plate 23 causes non-uniformity of the electric field on the lower surface of the electrode plate 23.
[0045]
Therefore, in this embodiment, instead of applying a DC voltage from the DC power supply, a high frequency having a frequency lower than that of the first high frequency power supply 60 is applied from the second high frequency power supply 63 to the upper electrode 21. Since the self-bias voltage due to the high frequency applied from the second high-frequency power source 63 is larger than the self-bias voltage due to the high frequency applied from the first high-frequency power source 60, the self-bias voltage from the first and second high-frequency power sources 60 and 63 By superimposing the high frequency, it is possible to obtain an extremely high self-bias voltage (V _dc ) compared to the case where the high frequency is applied only from the first high frequency power supply 60, and the contribution of FIG. As in the case, a thicker plasma sheath is formed, and the degree of non-uniformity of the self-bias voltage (V _dc ) and of the plasma sheath can be reduced. Therefore, the plasma density can be made uniform and the etching rate distribution can be made uniform.
[0046]
For example, when high frequency power of 60 MHz and 1 kW is applied from the first high frequency power supply 60 to the electrode 21, when V _dc = −100 V and the variation of V _dc is about ± 10 V, the variation ratio Becomes considerably large as ± 10%, and the uniformity of the plasma is lowered.
[0047]
However, when high frequency power of 2 MHz and 500 W, for example, is superimposed from the second high frequency power supply 63 to the electrode 21, V _dc by the second high frequency power supply 63 is about −400 V, and the overall V _dc is − ( 100 + 400) V ± 10V, and the variation rate of V _dc is ± 2%, and the uniformity of V _dc is improved. As a result, plasma uniformity is also improved.
[0048]
The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the above embodiment, a high frequency is applied to the upper and lower electrodes, but a type in which a high frequency is applied only to the upper electrode may be used. Moreover, although the case where a semiconductor wafer is used as the substrate to be processed and the oxide film on the wafer is etched has been described, the present invention is not limited to this, and the present invention is applicable to other etching such as an insulating film other than the oxide film and polysilicon. Can do. Furthermore, the processing target is not limited to the wafer, but may be another substrate such as a liquid crystal display (LCD) substrate.
[0049]
【The invention's effect】
As described above, according to the present invention, a high frequency having a frequency higher than 27 MHz is applied to the first electrode, and a DC voltage is further applied to the first electrode. (V _dc ) increases, the plasma sheath becomes thicker, and the degree of non-uniformity of the plasma sheath due to non-uniformity of the self-bias voltage (V _dc ) can be reduced. Therefore, the plasma density can be made uniform and the etching rate distribution can be made uniform.
[0050]
Further, a high frequency having a frequency higher than 27 MHz is applied to the first electrode from the first high frequency applying means, and a frequency lower than the frequency of the first high frequency applying means from the second high frequency applying means is applied to the first electrode. In the case of applying a high frequency, the self-bias voltage due to the high frequency applied from the second high-frequency applying means is larger than the self-bias voltage due to the high frequency applied from the first high-frequency applying means. Thus, it is possible to obtain a self-bias voltage (V _dc ) that is much higher than that of only the high frequency applied from the first high-frequency applying means, the plasma sheath becomes thick, and the self-bias voltage (V The degree of non-uniformity of the plasma sheath due to non-uniformity of _dc ) can be reduced. Therefore, the plasma density can be made uniform and the etching rate distribution can be made uniform.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a plasma etching apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram for explaining the principle of the present invention.
FIG. 3 is a sectional view showing a plasma etching apparatus according to a second embodiment of the present invention.
[Explanation of symbols]
1, 1 '; Etching apparatus 2; Chamber 5; Susceptor (second electrode)
6, 62; high-pass filter 21; upper electrode (first electrode)
30; Processing gas supply source 35; Exhaust device 40, 50, 60, 63; High frequency power source 41, 51, 61, 64; Matching unit 43; DC power source 44, 65; Low-pass filter S, S '; Wafer

Claims (8)

A chamber that accommodates a substrate to be processed;
An upper electrode and a lower electrode provided in parallel to face each other in the chamber;
High frequency applying means for applying a high frequency of 27 MHz or higher to the upper electrode;
DC voltage application means for applying a DC voltage to the upper electrode;
High frequency applying means for applying a high frequency of 100 kHz to 10 MHz to the lower electrode;
An exhaust means for maintaining the inside of the chamber at a predetermined reduced pressure state;
A processing gas introduction means for introducing a processing gas into the chamber;
A plasma of a processing gas is formed by forming a high-frequency electric field between the upper electrode and the lower electrode while the substrate to be processed is supported on the lower electrode, and a direct current from the DC voltage applying means is formed on the upper electrode. A capacitively coupled parallel plate plasma etching apparatus characterized in that a self-bias voltage on the surface of the upper electrode is increased by applying a voltage, and a plasma etching process is performed on the substrate to be processed by this plasma. A chamber that accommodates a substrate to be processed;
An upper electrode and a lower electrode provided in parallel to face each other in the chamber;
High frequency applying means for applying a high frequency of 27 MHz or higher to the upper electrode;
High frequency applying means for applying a high frequency of 100 kHz to 10 MHz to the lower electrode;
DC voltage application means for applying a DC voltage to the upper electrode;
An exhaust means for maintaining the inside of the chamber at a predetermined reduced pressure state;
A plasma etching method for performing plasma etching using a capacitively coupled parallel plate plasma etching apparatus provided with a processing gas introducing means for introducing a processing gas into the chamber,
A plasma of a processing gas is formed by forming a high frequency electric field between the upper electrode and the lower electrode while the substrate to be processed is supported on the lower electrode, and a direct current from the DC voltage applying means is applied to the upper electrode. A plasma etching method comprising applying a voltage to increase a self-bias voltage on the surface of the upper electrode and subjecting a substrate to be processed to plasma etching. 2. The capacitively coupled parallel plate plasma etching apparatus according to claim 1, wherein a low pass filter is provided between the upper electrode and the DC voltage applying means. The upper electrode includes an electrode plate constituting the opposing surfaces of the lower electrode, the capacitance according to claim 1 or claim 3, characterized in that it is constituted by an electrode support for supporting the electrode plate Combined parallel plate plasma etching system. The capacitive coupling according to claim 4 , wherein the electrode plate has a plurality of discharge holes, and the processing gas is discharged between the upper electrode and the lower electrode through the plurality of discharge holes. Mold parallel plate plasma etching equipment. The plasma etching method according to claim 2 , wherein a low pass filter is provided between the upper electrode and the DC voltage application unit. The said upper electrode is comprised by the electrode plate which comprises the opposing surface with the said lower electrode, and the electrode support body which supports this electrode plate, The plasma of Claim 2 or Claim 6 characterized by the above-mentioned. Etching method. The plasma etching method according to claim 7 , wherein the electrode plate has a plurality of discharge holes, and the processing gas is discharged to the substrate to be processed through the plurality of discharge holes.

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