JP2011061048A - Plasma treatment apparatus - Google Patents

Abstract

Provided is a means for controlling a stable electrostatic attraction voltage even when a harmonic component is generated on a high-frequency power transmission line due to the influence of a plasma load and waveform distortion occurs.
A lower electrode on which a wafer is placed in a vacuum vessel, a DC power source that electrostatically attracts a wafer to the electrode, a high-frequency bias power source connected to the lower electrode, an upper electrode, A plasma generating high frequency power supply 101 connected to the electrode and a high frequency voltage Vpp detecting means 119 for detecting the high frequency voltage Vpp applied to the lower electrode, and controlling the electrostatic attraction force of the wafer within a predetermined range. Therefore, in the plasma processing apparatus that controls the DC voltage for electrostatic adsorption using Vpp, the high frequency voltage Vpp detection means includes a fundamental wave component Vpp detection means 115 for detecting a fundamental frequency component of Vpp, and an average value of Vpp. Mean value Vpp detecting means 116 for detecting, and effective value Vpp detecting means 117 for detecting the effective value of Vpp are provided.
[Selection] Figure 1

Description

  The present invention relates to a plasma processing apparatus, and more particularly to a plasma processing apparatus suitable for performing surface treatment of a semiconductor element or the like using plasma.

In Patent Document 1, the high frequency voltage Vpp applied to the substrate electrode is monitored, and the voltage applied to the electrostatic adsorption film is controlled by controlling the output voltage of the electrostatic adsorption DC power source based on the monitored Vpp signal. It is disclosed to maintain the desired value. Next, (referred to as less V _pp) peak-to-peak voltage of the high frequency bias power supply 110 and a description will be given of the relationship of the self-bias voltage (hereinafter referred to as V _dc).

In FIG. 2, a DC voltage is applied to the electrostatic chucking electrode 109 by a DC power supply 107 for electrostatic chucking. This voltage value is referred to as an electrostatic adsorption DC voltage (hereinafter referred to as an ESC voltage). By applying the output of the high frequency bias power supply 110 to the electrostatic chucking electrode 109 via a capacitor, the average potential of the semiconductor wafer 113 becomes equal to V _dc which is a negative DC voltage. At this time, a potential difference between the electrostatic adsorption film 108 and the semiconductor wafer 113, that is, a difference between the ESC voltage and _Vdc becomes an electrostatic adsorption voltage (hereinafter referred to as V _chuck ). Further, V _dc depends on V _pp of the high frequency bias power supply 110 applied to the electrostatic adsorption film 108 and has a relationship as shown in the following equation.

  α is a constant that varies depending on the apparatus, and is about 0.3 to 0.45 in a general plasma processing apparatus.

Next, the relationship between V _chuck and the ESC voltage will be described with reference to FIG. FIG. 3 shows the relationship between the ESC voltage, V _dc , V _pp of the high frequency bias power supply 110 and V _chuck . The negative voltage V _dc appears on the negative side with a positive value that is α times as large as V _pp of the high-frequency bias power supply 110. It can be seen that there are two ESC voltages that produce the same V _chuck with respect to the value of V _dc, the positive side and the negative side. Here, the positive ESC voltage with respect to V _dc is referred to as V _ESC ^+, and the negative ESC voltage is referred to as V _ESC ⁻ .

At this time, the relationship between the ESC voltage and V _chuck and V _dc is expressed by the following equation.

However, V _dc is negative and V _chuck is a positive value. Which ESC voltage to use is selected according to abnormal discharge countermeasures, electrode substrate breakdown voltage, and specifications of the device (DC power supply for electrostatic adsorption). Which ESC voltage is used is set in advance by the ESC voltage control unit 114, and the ESC voltage control unit 114 detects the high frequency bias power supply 110 detected by the bias high frequency power supply Vpp voltage monitor detection circuit 112. From V _pp , V _dc is calculated by equation (1), and an ESC voltage output command is issued to the electrostatic chucking DC power source 107 so that V _chuck is substantially constant according to equation (2).

Next, problems due to plasma discharge will be described. Since the plasma 106 is a non-linear load, harmonics are generated. Due to the influence of the harmonics, there is a problem that the reliability of the peak-to-peak voltage (V _pp ) of the high-frequency bias power supply 110 detected by the bias high-frequency power supply peak-to-peak voltage monitor detection circuit 112 is lowered.

  Therefore, in the conventional apparatus, there is a possibility that the high frequency power supply malfunctions due to harmonic components generated by plasma discharge or modulated waves generated by the introduction of a plurality of high frequency powers. A technique for removing the is disclosed. Further, in Patent Document 3, since the introduction of a plurality of high-frequency powers causes the peak-to-peak voltage of other frequencies to coexist, the reliability of the peak-to-peak voltage value detected at the target frequency becomes low. And a technique for preparing a high-pass filter is disclosed.

JP 2008-71981 A JP 2003-179030 A JP 2008-41795 A

Next, FIGS. 4 and 5 show examples of waveform distortion images of the Vpp voltage of the high-frequency bias power supply 110 generated on the load side when harmonics are generated. In FIG. 4, it can be seen that the Vpp voltage of the former true Vpp 131 (solid line) is small between the actually generated true Vpp 131 (solid line) and Vpp ′ 132 (broken line) detected at the fundamental frequency. Conversely, in the example of the waveform distortion image of FIG. 5, it can be seen that the Vpp voltage of the former true Vpp 131 (solid line) is larger than Vpp ′ 132 (broken line) detected at the fundamental frequency. Therefore, in the detection of the Vpp voltage of the high-frequency bias power supply 110 using only the fundamental frequency, the true Vpp 131 (solid line) value may be erroneously detected. In order to calculate V _dc and determine the set value of the ESC voltage for ensuring a stable V _chuck , the reliability of the detected value of the Vpp voltage of the high-frequency bias power supply 110 increases the reliability of electrostatic adsorption. It will be influenced.

In the present invention, even when a harmonic component is generated on the transmission path of the high frequency bias power due to the influence of the plasma load and the waveform distortion occurs, the Vpp voltage of the high frequency bias power supply 110 generated in the electrostatic chucking electrode 109 is accurately determined. It is an object of the present invention to provide a plasma processing apparatus that controls the voltage to a desired V _chuck by detecting the current.

The present invention includes a vacuum vessel, a lower electrode on which a wafer is placed in the vacuum vessel, a DC power source for electrostatically attracting the wafer applied to the lower electrode, a high-frequency bias power source applied to the lower electrode, An upper electrode facing the lower electrode; a high frequency power source for plasma generation applied to the upper electrode; and a high frequency voltage Vpp detection circuit for detecting a high frequency voltage Vpp applied to the lower electrode, In the plasma processing apparatus for controlling the DC voltage for electrostatic adsorption using the Vpp in order to make the electroadsorption force constant,
The high frequency voltage Vpp detection circuit includes a fundamental wave component Vpp detection circuit that detects a fundamental frequency component of the high frequency power Vpp, an average value Vpp detection circuit that detects an average value of the high frequency bias power Vpp, and the high frequency bias power. And an effective value Vpp detection circuit for detecting an effective value of Vpp.

  By using the method of detecting the Vpp voltage of the high-frequency bias power of the present invention, even when a harmonic component is generated on the transmission path of the high-frequency bias power due to the influence of the plasma load and waveform distortion occurs, the accurate high-frequency bias power can be generated. By detecting the Vpp voltage, stable electrostatic chucking voltage control is possible.

Schematic of the plasma etching apparatus of the present invention. The block diagram of the conventional plasma etching apparatus. The relationship figure of Vpp voltage value of high frequency bias electric power, electrostatic adsorption voltage, and electrostatic adsorption power supply voltage. An example of a Vpp voltage waveform of high-frequency bias power generated on the load side. The other example of the Vpp voltage waveform of the high frequency bias electric power which generate | occur | produces on the load side. The functional block diagram of the ESC voltage control part of this invention. The functional flowchart of the determination part in the ESC voltage control part of this invention.

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

Here, FIG. 1 is a schematic view of the plasma etching apparatus of the present invention. The vacuum vessel 105 includes a flat antenna electrode 103 that is an aluminum conductor and a derivative 104 made of quartz that can transmit electromagnetic waves. The vacuum vessel 105 surrounds a processing chamber and generates a magnetic field. A coil 120 is provided. The antenna electrode 103 has a porous structure for flowing an etching gas. Fluorocarbon gases such as CF ₄ , C ₄ F ₆ , C ₄ F ₈ , C ₅ F ₈ , CHF ₃ and CH ₂ F ₂ , inert gases such as Ar and N ₂ , and oxidation-containing gases such as O ₂ and CO Then, it is controlled by a flow rate adjusting means (not shown) made of MFC provided in the gas supply device 118 and introduced into the vacuum vessel 105 through the gas supply device 118. Further, a vacuum evacuation device 123 is connected to the vacuum vessel 105, and a vacuum evacuation means (not shown) including a turbo molecular pump (TMP) provided in the vacuum evacuation device and a pressure adjusting means including automatic pressure control (APC). The inside of the vacuum vessel 105 is held at a predetermined pressure by (not shown). A high-frequency power source 101 (frequency 100 MHz to 450 MHz) for plasma generation is connected to the upper part of the antenna electrode 103 via a matching unit 102 and a coaxial cable 121. An electrostatic chucking electrode 109 on which a semiconductor wafer 113 can be placed is provided in the lower part of the vacuum vessel 105. The electrostatic chucking electrode 109 has an electrostatic chucking function for electrostatically chucking the semiconductor wafer 113 and is connected to a DC power source 107 for electrostatic chucking.

  Further, a high-frequency bias power source 110 (frequency 400 kHz to 5 MHz) for ion attraction is connected to the electrostatic adsorption electrode 109 via a matching unit 111 and a coaxial cable 122. The matching unit 111 has a function of performing impedance matching so that high-frequency power of a predetermined frequency of the high-frequency bias power source 110 is efficiently input to the electrostatic chucking electrode 109. Similarly, the matching unit 102 has a function of performing impedance matching so that high-frequency power of a predetermined frequency of the high-frequency power source 101 for generating plasma is efficiently input into the vacuum vessel 105.

The means for detecting the Vpp voltage value of the high-frequency bias power includes a fundamental wave component detection circuit 115 that detects the Vpp voltage using the Vpp voltage value of the high-frequency bias power as a fundamental frequency component of the high-frequency bias power supply 110, and a high-frequency bias power. The bias high-frequency power supply Vpp voltage monitor detection circuit 119 includes an average value detection circuit 116 that detects the average value of the Vpp voltage and an effective value detection circuit 117 that detects the effective value of the Vpp voltage of the high-frequency bias power. Further, the Vpp voltage value detected by the fundamental wave component detection circuit 115, the Vpp voltage value detected by the average value detection circuit 116, and the Vpp voltage value detected by the effective value detection circuit 117 are determined by ESC voltage control. Monitored by the unit 124. Further, the embodiment shown in FIG. 1 is different from the prior art shown in FIG. The ESC voltage control unit 114 merely calculates and outputs an ESC voltage to be set to the electrostatic attraction DC power source 107 so that a predetermined V _chuck is obtained from the Vpp voltage value of the high frequency bias power. As shown in FIG. 6, the ESC voltage control unit 124 of the present invention uses any circuit based on values detected by the fundamental wave component detection circuit 115, the average value detection circuit 116, and the effective value detection circuit 117. A determination unit 201 that determines whether the detected value is a Vpp voltage value of the high-frequency bias power; a calculation unit 202 that calculates an ESC voltage that is set for the electrostatic adsorption DC power source 107 based on the determined value; The ESC voltage is output as a command value to the database 203 for storing the determination result of the determination unit 201 and the calculation result calculated by the calculation unit 202, and to the DC power supply 107 for electrostatic adsorption. The voltage command unit 204 has a function of The operations of the fundamental wave component detection circuit 115, the average value detection circuit 116, the effective value detection circuit 117, and the operation of the ESC voltage control unit 124 in the bias high frequency power supply Vpp voltage monitor detection circuit 119 will be described below.

  The fundamental wave component detection circuit 115 is a fundamental frequency component of the high frequency bias power supply 110 and has a function of detecting the Vpp voltage value of the high frequency bias power. The average value detection circuit 116 has a function of detecting the voltage of the high frequency power supply for bias with the average value. Further, the effective value detection circuit 117 has a function of detecting the voltage of the bias high frequency power supply using the effective value. Next, the ESC voltage control unit 124 determines which value of the Vpp voltage of the high-frequency bias power detected by each of the detection circuits is used to determine the ESC voltage by the determination unit 201. One example will be described below with reference to FIG. First, using a dummy wafer, plasma is generated for each process condition to be used. Check the magnitude of the harmonic component generated for each process condition in advance, and the harmonic component generation level is lower than a certain level of the fundamental frequency component (the harmonic generation level is the traveling wave power of the fundamental frequency component). In the case of a process condition of a level (less than −30 dB of Pf), the fact that the ESC voltage is controlled by the Vpp voltage of the high frequency bias power detected by the fundamental wave component detection circuit 115 is stored in the database 203. In the case of a process condition where the harmonic component generation level is higher than a certain level of the fundamental frequency component (the harmonic generation level is greater than −30 dB of the traveling wave power Pf of the fundamental frequency component), the average value The ESC voltage is controlled by the value detected by the detection circuit 116 or the value detected by the effective value detection circuit 117.

  Further, in the determination means, the generation level of the harmonic component is not a determination method based on the level of a certain level of the fundamental frequency component, but the level of the waveform distortion rate level of the high frequency bias power (in Equation (3), the distortion rate is It is also possible to use a means for judging at 0.1 or less.

次に平均値検出回路１１６で検出した高周波バイアス電力の電圧値と、実効値検出回路１１７で検出した高周波バイアス電力値の電圧値のどちらを使用するかの判定手法のひとつとして、以下に説明する。負荷側に発生する高周波バイアス電源１１０のＶpp電圧の波形において、１周期内の正負の振幅が対称の場合は、平均値検出回路１１６で検出した高周波バイアス電力の電圧値で制御することとし、逆に１周期内の正負の振幅が非対称の場合は、実効値検出回路１１７で検出した高周波バイアス電力の電圧値で制御するといった方法がある。

Next, as one of the determination methods for using the voltage value of the high frequency bias power detected by the average value detection circuit 116 or the voltage value of the high frequency bias power detected by the effective value detection circuit 117, a description will be given below. . In the waveform of the Vpp voltage of the high-frequency bias power supply 110 generated on the load side, when the positive and negative amplitudes in one cycle are symmetric, control is performed with the voltage value of the high-frequency bias power detected by the average value detection circuit 116, and vice versa. When the positive and negative amplitudes in one cycle are asymmetric, there is a method of controlling with the voltage value of the high frequency bias power detected by the effective value detection circuit 117.

  The operation of the calculation unit 202 will be described. The Vpp voltage value of the high frequency bias power detected by the fundamental wave component detection circuit 115, the average value detected by the average value detection circuit 116, and the effective value detected by the effective value detection circuit 117 are stored in the database 203. The arithmetic unit 202 corrects and calculates the average value detected by the average value detection circuit 116 and the effective value detected by the effective value detection circuit 117 to the Vpp voltage value of the high-frequency bias power. The corrected value is stored in the database 203.

  Next, a method for calculating a correction coefficient for correcting the high-frequency bias power to the Vpp voltage from the detected average value and effective value will be described below. First, plasma is generated using a dummy wafer. At that time, it is desirable that the plasma to be used has a process condition in which almost no harmonic component is generated, and for example, the harmonic generation level is lower than the traveling wave power Pf of the fundamental frequency component by −30 dB. First, the Vpp voltage of the high frequency bias power at the fundamental frequency component detected by the fundamental wave component detection circuit 115 is stored in the database 203. Next, the calculation unit 202 stores the Vpp voltage of the high frequency bias power at the fundamental frequency component detected by the fundamental wave component detection circuit 115 stored in the database 203 and the high frequency bias power detected by the average value detection circuit 116. A correction coefficient is calculated so that the average value of the Vpp voltage becomes an equivalent value. The correction coefficient is stored in the database 203 as a correction for calculating the Vpp voltage of the high-frequency bias power detected from the average value of the Vpp voltage. Similarly, the arithmetic unit 202 stores the Vpp voltage of the high frequency bias power at the fundamental frequency component detected by the fundamental wave component detection circuit 115 stored in the database 203 and the high frequency bias power detected by the effective value detection circuit 117. A correction coefficient for calculating an effective value of the Vpp voltage is calculated. The correction coefficient is stored in the database 203 as a correction coefficient for calculating the Vpp voltage of the high-frequency bias power detected from the effective value of the Vpp voltage.

  As described above, the correction coefficient is calculated so that the detection values of the respective Vpp voltage detection circuits are equivalent in a state where the level of the harmonic component is sufficiently small, and is stored in the database 203. Although the correction coefficient calculation means for the plasma load using a dummy wafer has been described here, there is also a method for calculating the correction coefficient in advance in an environment in which, for example, a 50Ω dummy load is connected and no harmonic component is present. is there.

  Next, as described above, the arithmetic unit 202 corrects the average value of the Vpp voltage of the high frequency bias power detected by the average value detection circuit 116 and the high frequency bias detected by the effective value detection circuit 117. The correction coefficient that multiplies the effective value of the Vpp voltage of the power by the average value of the Vpp voltage and the effective value of the Vpp voltage, respectively, and the ESC voltage control unit 124 determines the Vpp voltage of the corrected high-frequency bias power of the average value. Vpp voltage of the high frequency bias power detected by three means of the corrected effective value of the high frequency bias power Vpp voltage and the Vpp voltage of the high frequency bias power at the fundamental frequency component detected by the fundamental wave component detection circuit 115 Are stored in the database 203.

Then, the voltage command unit 204 obtains V _{dc according} to Equation (1) from the determination result of the determination unit 201 stored in the database 203 and the Vpp voltage of the high frequency bias power stored in the database 203, and according to Equation (2). The ESC voltage calculated based on real time or a predetermined cycle is automatically controlled so that a desired V _chuck applied to the electrostatic adsorption film 108 can be controlled within a predetermined range. The predetermined cycle mentioned above is such that the ESC voltage is controlled at a cycle of 1 s. The control cycle can be set arbitrarily.

  According to the above embodiment, the fundamental wave component detection circuit 115, the average value detection circuit 116, and the effective value detection circuit 117 are prepared as a method for detecting the Vpp voltage of the high-frequency bias power generated in the electrostatic chucking electrode 109. The Vpp voltage value of the corrected high-frequency bias power is calculated from the values detected by the respective circuits by the calculation unit 202 of the ESC voltage control unit 124, stored in the database 203, and determined by the ESC voltage control unit 124. The unit 201 determines which circuit to use the Vpp voltage of the high-frequency bias power detected by which circuit based on the magnitude of the harmonic level generated for each process condition and the state of waveform distortion, thereby generating a harmonic by a non-linear plasma load. Even when a wave is generated, stable electrostatic adsorption voltage control can be performed.

  In the embodiments described above, an etching apparatus having a high frequency power source for plasma generation, a high frequency power source for biasing ions to the electrostatic adsorption electrode, and a direct current power source for electrostatic adsorption for electrostatic adsorption has been described. High-frequency power is supplied to the electrostatic adsorption electrode such as a coupled plasma apparatus and a parallel plate type plasma apparatus, as well as an ashing apparatus and a plasma CVD apparatus, and the electrostatic adsorption film is used to attract the electrostatic adsorption electrode. The same effect can be obtained in other plasma processing apparatuses.

  In the above-described embodiment, the method for detecting the Vpp voltage of the high frequency power supply for biasing ions is described. However, the same means may be used for detecting the Vpp voltage of the high frequency power supply for generating plasma.

  In the above-described embodiment, the case where high-frequency power of two different frequencies of the high-frequency power source for generating plasma and the high-frequency power source for biasing ions of the electrostatic adsorption electrode is supplied has been described. There may be three or more.

  In the embodiment described above, the Vpp voltage of the high frequency bias power at the fundamental frequency component detected by the fundamental wave component detection circuit 115, the Vpp voltage of the high frequency bias power calculated from the average value, and the high frequency bias calculated from the effective value. The example in which the ESC voltage is controlled using any value of the power Vpp voltage has been described. However, the ESC voltage may be controlled using the average value of the three detected Vpp values. .

  In the above-described embodiment, the average value of the Vpp voltage of the bias high-frequency power source detected by the average value detection circuit 116 and the effective value of the Vpp voltage of the bias high-frequency power source detected by the effective value detection circuit 117 are calculated. Although the case where the ESC voltage is controlled using the values corrected in 202 has been described, a method of controlling the ESC voltage using the average value and effective value of the true Vpp voltage before correction may be used.

  In the above-described embodiment, the case where the ESC voltage control unit 124 controls the ESC voltage using the Vpp voltage of the high-frequency bias power determined in advance for each process condition has been described. When the plasma state changes and the harmonic generation level changes, the Vpp voltage of the selected high-frequency bias power stored in advance may be changed to control the ESC voltage.

DESCRIPTION OF SYMBOLS 101 High frequency power supply 102, 111 Matching device 103 Antenna electrode 104 Derivative 105 Vacuum vessel 106 Plasma 107 Electrostatic adsorption DC power supply 108 Electrostatic adsorption film 109 Electrostatic adsorption electrode 110 High frequency bias power supply 112, 119 Bias high frequency power supply Vpp voltage monitor detection Circuit 113 Semiconductor wafers 114 and 124 ESC voltage control unit 115 Fundamental wave component detection circuit 116 Average value detection circuit 117 Effective value detection circuit 118 Gas supply device 120 Magnetic field generating coils 121 and 122 Coaxial cable 123 Vacuum exhaust device 131 True Vpp
132 Vpp 'detected by fundamental frequency component
201 Determination Unit 202 Calculation Unit 203 Database 204 Voltage Command Unit

Claims (3)

A vacuum vessel, a lower electrode for mounting a wafer in the vacuum vessel, a DC voltage power source for electrostatically adsorbing the wafer to the lower electrode, a high-frequency bias power source applied to the lower electrode, and the lower electrode, An upper electrode opposed to the upper electrode; a high-frequency power source for plasma generation applied to the upper electrode; and a high-frequency voltage Vpp detection means for detecting the high-frequency voltage Vpp applied to the lower electrode, In the plasma processing apparatus for controlling the DC voltage for electrostatic adsorption using the high-frequency voltage Vpp in order to control the voltage within a predetermined range,
The high frequency voltage Vpp detection means includes a fundamental wave component Vpp detection means for detecting a fundamental frequency component of the high frequency voltage Vpp, an average value Vpp detection means for detecting an average value of the high frequency voltage Vpp, and an effective value of the high frequency voltage Vpp. An effective value Vpp detecting means for detecting a value.   The plasma processing apparatus according to claim 1, further comprising an electrostatic adsorption DC voltage control unit that controls the electrostatic adsorption DC voltage, wherein the electrostatic adsorption DC voltage control unit includes the fundamental wave component Vpp detection unit. Obtained from each of the average value Vpp detection means and the effective value Vpp detection means, a calculation section for calculating the DC voltage for electrostatic adsorption from the Vpp, and the determination section. A plasma processing apparatus comprising: a database for accumulating the determined determination results and the calculation results obtained from the calculation unit; and a voltage command unit for outputting the calculation results to the DC voltage power source.   In the said calculating part of the plasma processing apparatus of Claim 2, the average value of Vpp detected from each of the said fundamental wave component Vpp detection means, the said average value Vpp detection means, and the said effective value Vpp detection means is calculated, An average value is output to the DC voltage power supply.

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