JP4324541B2 - Plasma processing equipment - Google Patents

Description

  The present invention relates to a plasma processing technique, and more particularly, to a plasma processing technique capable of performing stable plasma processing by supplying a phase-controlled bias voltage to an antenna and a substrate of a plasma processing apparatus.

  In the manufacturing process of a semiconductor device, various processes using plasma such as an etching process, a CVD process, and an ashing process are performed. Together with higher integration and higher performance of semiconductor devices, these plasma treatments suitable for microfabrication have come to be frequently used in the manufacturing process. In an etching processing apparatus that forms grooves and patterns on the surface of a substrate to be processed such as a wafer, a parallel plate such as RIE (Reactive Ion Etching) formed by arranging an upper electrode and a lower electrode in a vacuum processing chamber facing each other. A plasma etching apparatus is used. When etching is performed using plasma, the processing gas can be ionized and activated to increase the processing speed. In addition, by supplying high frequency bias power to the substrate to be processed and causing ions in the plasma to be perpendicularly incident on the substrate to be processed, a highly accurate etching process such as an anisotropic shape can be realized.

  In a plasma processing apparatus that performs such processing, an air-core coil is provided on the outer peripheral portion outside the vacuum vessel, and a circular conductor plate is provided facing the sample stage provided in the vacuum vessel, and the UHF band is provided on the circular conductor plate. A power source and a first high-frequency power source are connected, and a second high-frequency power source is connected to the sample stage. In addition, an electric field having a frequency in the UHF band and an electric field having a frequency different from the frequency in the UHF band are superimposed and supplied to the circular conductor plate, and electron cyclotron resonance is caused by the interaction between the electromagnetic wave from the UHF band power source and the magnetic field from the air-core coil. A phenomenon is used to form a plasma. At this time, the bias applied to the circular conductor plate is increased by the high-frequency voltage generated by the first high-frequency power supply so that the circular conductor plate reacts with the plasma so that more active species contributing to etching can be generated. Moreover, the incident energy to the sample of the ion in plasma can be controlled by the 2nd high frequency power supply connected to the sample stand (for example, refer patent document 1).

  In such a plasma processing apparatus, an electric circuit of high-frequency power applied to the substrate to be processed is formed in a direction crossing the magnetic field. For this reason, a potential distribution is formed in the surface of the substrate to be processed due to the impedance of the plasma in the direction perpendicular to the magnetic field, and charging damage may occur. The ion energy incident on the substrate to be processed is determined by the self-bias potential generated by the bias power supplied to the substrate to be processed, but the ratio of the ground area to the substrate electrode decreases as the wafer size increases. Therefore, the bias application efficiency is reduced.

  In the conventional apparatus, the vacuum vessel is grounded. For this reason, plasma spreads in the vacuum vessel which is grounded and has an earth potential, and cannot be sufficiently confined in the processing portion in the vacuum vessel and diffuses to the outer peripheral portion. For this reason, sputtering of the inner wall of the vacuum vessel and attachment / detachment of reaction products occur, which may increase the amount of foreign matter generated.

  In recent years, as the degree of integration of semiconductor integrated circuits has increased, for example, the gate oxide film of a MOS (Metal Oxide Semiconductor) transistor, which is a typical example of a semiconductor element, has become thinner and the gate oxide film has a problem of dielectric breakdown (charging). (Damage) is getting serious. Further, with the miniaturization of semiconductor elements, it is required to improve the mask selection ratio with respect to processing accuracy, as represented by SAC (Self Aligned Contact). In addition, since the occurrence of foreign matter or the like in the apparatus lowers the yield and reduces the operating rate of the apparatus, an apparatus with a small amount of foreign matter is required.

  Therefore, a method of controlling plasma generated by applying high-frequency power having the same frequency and phase controlled between the upper electrode and the lower electrode has been attempted. According to this method, the potential distribution in the surface of the substrate to be processed due to the in-plane distribution of the plasma density can be reduced, and the occurrence of charging damage can be suppressed. In addition, by controlling the phase of the high frequency, the directivity and energy of ions incident on the substrate to be processed can be controlled, which improves the selectivity between the mask and the substrate to be processed, and enables high aspect ratio etching. Become.

  In addition, since the diffusion of plasma can be suppressed, the amount of foreign matter generated due to sputtering of the inner wall of the vacuum vessel and the attachment / detachment of reaction products to the inner wall of the vacuum vessel can be reduced, and the yield of semiconductor devices and the like can be improved. Furthermore, since the deposits on the inner wall of the vacuum vessel can be reduced, the maintenance cycle of the apparatus can be lengthened and the throughput can be improved.

Examples of documents related to this type of technology include Patent Document 2 and Patent Document 3. For example, Patent Document 2 discloses that control is performed while independently applying a high frequency of the same frequency to an upper electrode and a lower electrode that are provided opposite to each other in a vacuum chamber while controlling the phase. In Patent Document 3, a high-frequency voltage applied to an upper electrode and a lower electrode is provided with a preset position of a phase difference at the time of plasma ignition, and is controlled to a predetermined phase difference in view of plasma stability. . The timing for controlling to a predetermined phase difference is controlled by a switching timer provided in the phase control unit.
JP-A-9-321031 JP-A-8-162292 JP 2004-30931 A

  According to the technique described in Patent Document 2, a predetermined phase difference is set in the high frequency supplied to the upper electrode and the lower electrode, and feedback control is performed so as to maintain the phase difference. However, no consideration is given to the control method at the time of ignition where the plasma is unstable, and there is a problem in the stability of the plasma ignition. In addition, there is a problem in the stability of the plasma because it tends to fall from a plasma ignition state to a hunting state in which the plasma blinks during control to a predetermined phase difference.

  In the case of this example, it is necessary to stop the device when a problem occurs in plasma ignitability and plasma stability, and to tune the matching controller, etc. Become. Wafers processed in such an unstable state are susceptible to plasma damage due to non-uniform plasma density in the surface, and the processing shape becomes unstable, which significantly reduces the yield of semiconductor devices. become.

  Further, according to the technique described in Patent Document 3, the output power supply waveform (VPP) of each matching unit is fed back at a timing when a high frequency power application signal is received, and is controlled to a predetermined phase difference. However, no consideration is given to the transmission timing of the high-frequency power application signal and the power setting signal. For this reason, since control is started from a state where the output power supply waveform (VPP) is not detected, there is a problem in the stability of the phase control such as a malfunction of the phase control unit. This technique also causes the same manufacturing problems as described above.

  The present invention has been made in view of these problems, and provides a plasma processing technique capable of performing stable plasma processing by supplying a phase-controlled bias voltage to an antenna and a substrate of a plasma processing apparatus in a timely manner. To do.

  In order to solve the above problems, the present invention employs the following means.

  A gas supply means for supplying a processing gas into the vacuum processing container, a first high-frequency power source for generating plasma by supplying high-frequency energy to the upper antenna electrode disposed in the vacuum processing container, and an antenna bias for the upper antenna electrode A second high-frequency power source for supplying a voltage; a substrate electrode for mounting and holding a substrate to be processed in a vacuum processing vessel; and a high-frequency substrate bias voltage having the same frequency as that of the second high-frequency power source is supplied to the substrate electrode And a phase difference control unit that controls a phase difference between the second high frequency power source and the third high frequency power source, and the phase difference control unit is configured to transmit a traveling wave from the second high frequency power source. A detector for detecting a power value and a power value of a traveling wave from the third high-frequency power source, and a detector for detecting a phase of the second high-frequency power source and a phase of the third high-frequency power source; from When it is detected that the power value of the traveling wave and the power value of the traveling wave from the third high-frequency power source have reached preset values, the second high-frequency power source and the second high-frequency power source according to the preset phase difference initial value signal The phase difference between the second high frequency power supply and the third high frequency power supply is controlled after a predetermined time has elapsed from the start of the control by the phase difference control unit while controlling the phase difference with the third high frequency power supply. Feedback control is performed according to the signal.

  Since the present invention has the above-described configuration, stable plasma processing can be performed by supplying a phase-controlled bias voltage to the antenna and the substrate of the plasma processing apparatus in a timely manner.

  Hereinafter, the best embodiment will be described with reference to the accompanying drawings. FIG. 1 illustrates an example of a UHF plasma etching apparatus that forms plasma using a UHF (Ultra High Frequency) and a magnetic field as a plasma processing apparatus according to the present embodiment.

  The upper half of the vacuum vessel 101 is composed of a cylindrical upper processing vessel 104, a flat antenna electrode 103 made of a conductor such as aluminum or nickel, and a dielectric window 102 made of quartz, sapphire or the like that can transmit electromagnetic waves. Is done. This upper half part is airtightly placed on the opening part of the lower half part of the vacuum vessel 101 through a vacuum sealant 127 such as an O-ring, and forms a processing chamber 105 inside.

A magnetic field generating coil 114 is provided on the outer periphery of the upper processing vessel 104 so as to surround the processing chamber. The antenna electrode 103 has a porous structure for flowing an etching gas. In addition, Freon gas such as CF ₄ , C ₄ F ₆ , C ₄ F ₈ , C ₅ F ₈ , CHF ₃ and CH ₂ F ₂ , inert gas such as Ar and N ₂ , or oxygen such as O ₂ and CO The contained gas is introduced into the processing chamber 105 through the gas supply device 107 after the flow rate is adjusted by the flow rate adjusting means provided in the gas supply device 107. A vacuum exhaust device 106 is connected to the vacuum vessel 101, and the inside of the processing chamber 105 is held at a predetermined pressure by a vacuum exhaust means and a pressure adjusting means provided in the vacuum exhaust device 106.

  A coaxial line 111 is provided above the antenna electrode 103, and a high-frequency power source (first high-frequency power source) 108 (for example, a frequency of 450 MHz) for plasma generation is connected via the coaxial line 111, the filter 110, and the matching unit 109. The An antenna bias power source (second high frequency power source) 113 (for example, a frequency of 800 kHz) is connected to the antenna electrode 103 via a coaxial line 111, a filter 121, and a matching unit 112. Here, the filter 110 allows high-frequency power from the high-frequency power source 108 to pass and effectively cuts bias power from the antenna bias power source 113. The filter 121 allows the bias power from the antenna bias power supply 113 to pass therethrough and effectively cuts the high frequency power from the high frequency power supply 108.

  A substrate electrode 115 on which a substrate to be processed 116 can be disposed is provided in the lower part of the vacuum vessel 101. A substrate bias power source (third high frequency power source) 119 (for example, a frequency of 800 kHz) is connected to the substrate electrode 115 via a filter 117 and a matching unit 118. An electrostatic chuck power source 123 is connected to the substrate electrode 115 via a filter 122 to an electrostatic chuck electrode 124 for electrostatically attracting the substrate 116 to be processed. Here, the filter 117 passes the bias power from the substrate bias power source 119 and effectively cuts the high frequency power from the high frequency power source 108.

  Normally, the high frequency power from the first high frequency power supply is absorbed in the plasma and does not flow to the substrate electrode 115 side, but a filter 117 is provided for safety. Further, the filter 122 allows the DC power from the electrostatic chuck power source 123 to pass therethrough and effectively cuts the power from the high frequency power source 108, the antenna bias power source 113, and the substrate bias power source 119.

  The antenna bias power supply 113 and the substrate bias power supply 119 are connected to the phase control unit 120 so that the phase of the high frequency output from the antenna bias power supply 113 and the substrate bias power supply 119 can be controlled. The antenna bias power supply 113 and the substrate bias power supply 119 have the same frequency.

  FIG. 2 is a diagram illustrating a high-frequency supply circuit that supplies high-frequency power to the antenna and the substrate. In the figure, the same parts as those shown in FIG. First, a high frequency application signal is transmitted to the control microcomputer 144 from a control unit (not shown). The control microcomputer 144 includes a traveling wave power setting signal 133a, a phase difference initial setting signal 131, a target phase difference setting signal 132, a phase control unit 120 including a power frequency oscillation unit 130, a phase difference control unit 143, and a switching timer unit 145. A traveling wave power setting signal 134b is transmitted. The phase control unit 120 generates high-frequency command signals 135a and 136b having a predetermined phase difference between the antenna bias power source 113 and the substrate bias power source 119 according to the setting signal.

  The antenna bias power supply 113 and the substrate bias power supply 119 oscillate high-frequency power controlled to a predetermined phase in accordance with the input high-frequency signal 135a and high-frequency signal 136b, and pass through the matching unit 112 and the matching unit 118 to be a vacuum container. Electric power is applied to the antenna electrode 103 and the substrate electrode 115 inside. Thereby, the spatial distribution of the plasma to be formed and the ion energy incident on the substrate to be processed can be controlled.

  FIG. 3 is a diagram for explaining the operation of the plasma processing apparatus including the high-frequency power supply circuit shown in FIG. The operation will be described below with reference to FIGS.

  First, a predetermined process gas is introduced into the processing chamber 105 through the gas supply device 107. At this time, a predetermined coil current (for example, 10 A) is applied to the magnetic field generating coil 114 to generate a magnetic field. Further, the control microcomputer 144 sends a traveling wave power setting signal 133a (for example, 100 W) for the antenna bias power supply 113 and a traveling wave power setting signal 134b (for example, 100 W) for the substrate bias power supply 119 to the phase difference control unit 143. Transmit (time t1).

  Next, the internal pressure of the processing chamber 105 is adjusted to a predetermined value (for example, 2 Pa) by a vacuum exhaust unit and a pressure adjusting unit provided in the vacuum exhaust unit 106. After detecting that the pressure has reached a predetermined pressure (time t2), a predetermined power (for example, 500 W) is supplied from the high frequency power supply 108 for plasma generation to the matching unit 109, the filter 110, the coaxial line 111, and the coaxial waveguide 125. Then, it is supplied into the processing chamber 105 to generate plasma.

  After plasma generation at time t2 (for example, after 0.1 second), a predetermined voltage (for example, 200 V) is applied from the electrostatic chuck power source 123 to the electrostatic chuck electrode via the filter 122 (time t3).

  When predetermined power is supplied after the start of power supply from the plasma generating high-frequency power source 108 at time t2 (for example, 0.5 seconds later), predetermined power (for example, 100 W) is supplied from the antenna bias power source 113. Is supplied to the antenna electrode 103 via the matching unit 112, the filter 121, the coaxial line 111, and the coaxial waveguide 125 (time t4).

  Next, after detecting the ignition of the plasma 126 (time t5) (for example, after 0.5 seconds) by the ignition detection means comprising a photomultiplier substrate or the like, a predetermined power (for example, 100 W) is supplied from the substrate bias power source 119. 118 is supplied to the substrate 115 through the filter 117 (time t6).

  Next, the traveling wave power monitor value 141a from the antenna bias power supply 113 and the traveling wave power monitor value 142b from the substrate bias power supply 119 are monitored. The phase difference control unit 143 sets the traveling wave power monitor value 141a from the antenna bias power supply 113 and the traveling wave power monitor value 142b from the substrate bias power supply 119 as the traveling wave power setting signal 133a and the traveling wave power setting signal 134b, respectively. Is detected (when an AND condition is satisfied), a high-frequency command signal set to a value that satisfies the value indicated by the phase difference initial setting signal 131 (for example, 175 °) received from the control microcomputer 144 135a and the high-frequency command signal 136b are transmitted (time t7). The traveling wave power from the antenna bias power supply 113 and the traveling wave power from the substrate bias power supply 119 continue to be controlled so as to match the traveling wave power setting signal.

  The phase control unit 143 is detected by the phase detection unit 137 at the time (time t8) when the time (for example, 2 seconds) set by the switching timer unit 145 has elapsed since the AND condition is satisfied (time t7). The phase detection signal of the antenna bias power source and the phase detection signal of the substrate bias power source detected by the phase detection unit 138 are used as the feedback signal 139a and the feedback signal 140b. Further, the phase difference control unit 143 receives the target phase difference setting signal 132 (for example, 180 °) from the control microcomputer 144, and in accordance with the received target phase difference setting signal, the phase of the antenna bias power supply and the phase of the substrate bias power supply. The high-frequency command signal 135a and the high-frequency command signal 136b set so that the phase difference becomes the target phase difference are transmitted to the antenna bias power source 113 and the substrate bias power source 119 (time t8).

  As a result, the phase and traveling wave power of the antenna bias power supply 113 and the phase and traveling wave power of the substrate bias power supply 119 are automatically controlled to have a predetermined phase difference and power value, respectively.

  As described above, when power is applied from the antenna bias power supply 113 and the substrate bias power supply 119, a predetermined traveling wave power setting signal is set, and a phase difference initial setting that is a phase difference suitable for discharge ignition is set. High-frequency power can be supplied with a signal (for example, 175 °) set. Further, when it is detected that the traveling wave power from the antenna bias power supply 113 and the substrate bias power supply 119 has reached a preset power value, that is, when the AND condition is satisfied, a preset phase difference initial setting value is set. Control of the phase difference between the antenna bias power supply 113 and the substrate bias power supply 119 is started in accordance with the signal. Further, after a lapse of a predetermined time from the start of this control, the phase difference between the antenna bias power supply 113 and the substrate bias power supply 119 is detected via the phase detectors 137 and 138, and this detected value is used as the target phase difference setting signal. Start feedback control to match.

  Thus, traveling wave power monitor value 141a from antenna bias power supply 113 and traveling wave power monitor value 142b from substrate bias power supply 119 are set values set by traveling wave power setting signal 133a and traveling wave power setting signal 134b, respectively. The phase control based on feedback is started when it is detected that the above condition is met, that is, when the AND condition is satisfied. That is, since feedback control is started after detecting a traveling wave that is equal to or greater than a preset value, malfunction of the phase control unit can be prevented. The set value can be set from the outside.

  Further, the stability of the plasma can be maintained even when the plasma is unstablely ignited or during the transition period when the plasma is ignited and controlled to the target phase difference. In this way, by stabilizing the plasma, tuning work during the etching process can be avoided, so that the productivity of the plasma processing apparatus can be improved. In addition, it is possible to suppress a decrease in yield of a semiconductor device or the like due to a processing shape defect due to plasma instability or plasma damage.

  In addition, by applying high-frequency power having a stable phase difference, the directivity and energy of ions incident on the substrate to be processed are stably controlled, and the variation in the selection ratio between the mask and the substrate to be processed is reduced. Etching with a high aspect ratio is possible. In addition, since the occurrence of charging damage due to the in-plane distribution of plasma density can be suppressed, the yield of semiconductor devices and the like can be improved.

  Furthermore, since plasma diffusion is suppressed, spatter and deposits on the inner wall of the vacuum vessel are reduced, and reduction in yield of semiconductor devices and the like due to foreign matters can be suppressed. Moreover, since the deposits on the inner wall of the vacuum vessel are reduced, the maintenance cycle of the apparatus becomes longer, and the productivity of the apparatus can be improved.

  Although the target phase difference in this embodiment is 180 °, the optimum phase difference is selected according to the process to be used and the required processing shape, and the directivity and ion energy of ions incident on the substrate to be processed are selected. It is desirable to control.

It is a figure explaining the UHF plasma etching apparatus as a plasma processing apparatus which concerns on this embodiment. It is a figure explaining the high frequency supply circuit which supplies high frequency electric power to an antenna and a board | substrate. It is a figure explaining operation | movement of the plasma processing apparatus containing the high frequency supply circuit shown in FIG.

Explanation of symbols

101 Vacuum container 102 Dielectric window 103 Antenna electrode 104 Upper processing container
105 Processing chamber 106 Vacuum exhaust device 107 Gas supply device 108 High frequency power source for plasma generation (first high frequency power source)
109 Matching device 110 Filter 111 Coaxial line
112 Matching device 113 Antenna bias power source (second high frequency power source)
114 Magnetic field generating coil
115 Substrate electrode 116 Substrate 117 Filter 118 Matching device
119 Substrate bias power supply (third high frequency power supply)
120 Phase control unit 121 Filter
122 Filter 123 Electrostatic chuck power supply 124 Electrostatic chuck electrode
125 Coaxial waveguide 126 Plasma 127 Vacuum seal material 130 Frequency generator
144 Microcomputer 145 Switching timer section

Claims (3)

A gas supply means for supplying a processing gas into the vacuum processing container;
A first high-frequency power supply for generating plasma by supplying high-frequency energy to an upper antenna electrode disposed in a vacuum processing container;
A second high frequency power source for supplying an antenna bias voltage to the upper antenna electrode;
A substrate electrode for mounting and holding a substrate to be processed in a vacuum processing container;
A third high frequency power source for supplying a high frequency substrate bias voltage having the same frequency as that of the second high frequency power source to the substrate electrode;
A phase difference control unit for controlling a phase difference between the second high frequency power source and the third high frequency power source;
The phase difference control unit detects a traveling wave power value from the second high frequency power source and a traveling wave power value from the third high frequency power source, and a phase and third phase of the second high frequency power source. Equipped with a detector to detect the phase of the high frequency power supply,
When it is detected that the power value of the traveling wave from the second high-frequency power source and the power value of the traveling wave from the third high-frequency power source have reached preset values, a preset phase difference initial setting value signal And controlling the phase difference between the second high frequency power source and the third high frequency power source according to
A plasma processing apparatus, wherein after a predetermined time has elapsed from the start of the control by the phase difference control unit, the phase difference between the second high frequency power supply and the third high frequency power supply is feedback controlled according to a target phase difference setting signal. The plasma processing apparatus according to claim 1,
The phase difference control unit includes a switching timer for switching the phase difference between the second high frequency power source and the third high frequency power source to feedback control according to the target phase difference setting signal after a predetermined time has elapsed from the start of the control. A plasma processing apparatus. The plasma processing apparatus according to claim 1,
The plasma processing apparatus, wherein the set value of the traveling wave power value can be set from outside.

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