JP2006073723A - Plasma treatment device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide plasma treatment technology capable of impressing a stabilized and required voltage waveform on an object to be treated. <P>SOLUTION: The plasma treatment device is provided with a treatment gas introducing port 5, a vacuum exhausting means 2 and a stage 6 for mounting a specimen to convert the introduced treatment gas into plasma and apply plasma treatment on a specimen. The plasma treatment device is provided with a high-frequency voltage generating means 8 for supplying high-frequency power to the stage 6 and accelerating an ion incident to the specimen, a voltage sensor 10 for detecting a high-frequency voltage supplied to the stage and controlling a high-frequency voltage generating means so that the voltage becomes a set value, and a fixed impedance circuit 9 connected in parallel to the stage to serve as the load of the high-frequency voltage generating means 8 while the value of the impedance of the fixed impedance circuit is set so that power supplied to the side of the fixed impedance circuit becomes more than 50% of the output of the high-frequency voltage generating means 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plasma processing technique, and more particularly to a plasma processing technique capable of obtaining a processing performance without variations.

  Corresponding to miniaturization of semiconductor devices, process conditions (process windows) capable of realizing a uniform processing result within a wafer surface are becoming narrower year by year in plasma processing apparatuses. For this reason, the plasma processing apparatus is required to control the process state more completely. In order to realize this, an apparatus capable of controlling the plasma distribution, the dissociation of the process gas, or the surface reaction in the processing chamber with extremely high accuracy is required.

  Many plasma processing apparatuses normally supply a high-frequency voltage of several hundreds of kHz to several tens of MHz to a stage that holds the object to be processed to control ion energy incident on the object to be processed. In addition, the energy of ions incident on the object to be processed can be controlled by changing the high-frequency voltage applied to the object to be processed.

  It is the voltage that controls the ion energy. However, since it is difficult to accurately adjust the amplitude of the high frequency voltage, from the viewpoint of repeated processing stability, for example, ion energy control for controlling high frequency power is widely used as disclosed in Patent Document 1. It has been. Further, in recent years, high-frequency voltage control (peak-to-peak voltage is often used, so in this specification, referred to as Vpp control) has come to be used. For example, Patent Documents 2 and 3 show that the power source is controlled so as to keep the Vpp voltage constant, and the etching rate of the workpiece is always kept constant. Patent Document 4 shows that voltage control and power control are switched as necessary.

  FIG. 8 is a diagram for explaining a conventional plasma processing apparatus. In the figure, a processing chamber 1 is, for example, an aluminum or stainless steel vacuum vessel whose surface is anodized, and is electrically grounded. The processing chamber 1 includes a vacuum evacuation unit 2 and a transfer system 4 for loading and unloading a semiconductor wafer 3 that is an object to be processed. A stage 6 for placing the semiconductor wafer 3 is installed in the processing chamber 1. The wafer is loaded into the processing chamber by the transfer system 4 and held on the stage 6. The stage 6 is usually provided with an electrostatic chuck, and securely holds the semiconductor wafer electrically and thermally.

  Etching gas is introduced into the chamber through the gas inlet 5. Further, a high frequency voltage generating means 8 is connected to the stage 6 to control the energy of ions incident on the semiconductor wafer 3 during plasma processing. The high-frequency voltage generation means 8 is a normal high-frequency power source when the required waveform may be a single waveform such as a sine wave. When an arbitrary waveform is required, it is configured by a combination of an arbitrary waveform generator and an amplifier. The voltage sensor 10 feeds back the output to the high-frequency voltage generating means 8 and controls the output value of the high-frequency voltage generating means 8 so that the voltage applied to the stage 6 is constant.

An automatic matching unit 13 is provided between the high-frequency voltage generation means 8 and the stage 6. The automatic matching unit 13 includes a variable capacitor and a variable inductor, and adjusts them with a motor to achieve impedance matching with a load. Thereby, the high frequency power from the high frequency voltage generating means 8 can be efficiently put into the processing chamber.
JP 11-330059 A JP-A-5-234955 JP-A-8-199378 Japanese Patent No. 3350389

  In recent LSI manufacturing processes, high accuracy of process control and repeated stability are the most important. For example, considering the superiority or inferiority of the above-mentioned Vpp control and power control used for controlling the ion energy incident on the object to be processed, the Vpp control is a parameter that indicates ion energy more directly than the power control. Can be controlled based on. However, the value of Vpp control is likely to vary due to waveform distortion or the like. For this reason, the power control can perform more stable control.

  Also, recent plasma processing has a short processing time. For this reason, variation in behavior at the start of processing for each processing greatly affects the processing result. For example, as described above, the high-frequency power source includes the automatic impedance matching unit 13 between the load (stage in the case of a plasma apparatus). When power is supplied from a high-frequency power source, impedance matching is performed by operating a variable inductance or variable capacitor in the automatic matching unit with a motor or the like. When matching is achieved, predetermined power can be supplied to the load.

  In order to obtain a good plasma treatment, it is effective to control not only the average value of the ion energy incident on the workpiece but also the distribution of the ion energy. For example, S. of Journal of Appled Physics, vol88 no2, p643, 15 july 2000, -B. Wang and A.W. E. As shown in Wendt's paper, etc., the band of the ion energy distribution can be narrowed by making a high-frequency waveform applied to the object to be processed into a pulse shape with a low duty ratio. . If the energy of ions is aligned in this way, for example, in plasma etching, an etching process with higher anisotropy becomes possible.

  However, even if a voltage having a desired waveform is generated by the voltage generating means in this way, the voltage waveform generated on the surface of the object to be processed varies depending on the impedance component of the stage or the impedance component of the plasma or ion sheath. Resulting in.

FIG. 9 is a diagram for explaining an equivalent circuit of the plasma processing apparatus shown in FIG. The impedance Z _{ST of the} stage 6 includes an internal resistance R _ST, an inductance L _{ST of the} wiring route _{, a} parasitic capacitance C _{ST, and the} like. Since these values are constant unless the stage structure is changed, the impedance _ZST of the stage is considered to be a constant value. On the other hand, the impedance _ZPL including the plasma above the wafer is composed of a plasma resistance R _PL , a wafer-plasma ion sheath capacitance C _S1 , a ground-plasma ion sheath capacitance C _{S2, and the} like. However, these vary depending on the discharge state. For this reason, the load impedance Z _LOAD composed of these impedances changes depending on the state of the plasma. In response to this change, the automatic impedance matching unit 13 adjusts the internal variable capacitor and variable inductance so that the current efficiently flows through the circuit shown in FIG.

  By the way, when adjusting the variable capacitor and the variable inductance in the automatic matching device, it takes several seconds until the matching is achieved because the elements constituting them are driven by a motor or the like. On the other hand, since many of the recent plasma processes have a short processing time, variations in the process until alignment at the start of the processing is taken have a great influence on the processing result. That is, the repeated stability of the alignment process performed for each wafer greatly affects the processing result.

  The present invention has been made in view of these problems, and provides a plasma processing technique capable of accurately and quickly applying a stable desired voltage waveform to an object to be processed.

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

    In a plasma processing apparatus that includes a processing gas inlet, a vacuum exhaust means, and a stage on which a sample is placed, and converts the introduced processing gas into plasma and applies plasma processing to the sample, high frequency power is supplied to the stage and incident on the sample A high-frequency voltage generating means for accelerating ions, a voltage sensor for detecting a high-frequency voltage supplied to the stage and controlling the high-frequency voltage generating means so that the voltage becomes a set value, and connected in parallel to the stage; A fixed impedance circuit acting as a load of the high frequency generating means was provided, and the impedance of the fixed impedance circuit was set so that the power supplied to the fixed impedance circuit side was 50% or more of the output of the high frequency voltage generating means.

  Since this invention is provided with the above structure, the stable desired voltage waveform can be applied to a to-be-processed object.

  FIG. 1 is a diagram illustrating a plasma processing apparatus according to an embodiment of the present invention. In the figure, the same parts as those shown in FIG.

  As shown in the figure, a voltage sensor 10 for measuring a voltage applied to the stage 6 is provided. The voltage sensor 10 feeds back the output to the high-frequency voltage generating means 8 and controls the output value of the high-frequency voltage generating means 8 so that the voltage applied to the stage 6 is constant.

  In the present invention, a semi-fixed matching circuit 11 capable of finely adjusting the impedance is provided instead of the conventional automatic matching device. A fixed impedance circuit 9 is connected in parallel to the stage. In other words, the connection between the stage, which is the main power supply circuit for supplying the wafer bias, and the ground is bypassed. The fixed impedance circuit 9 is preferably made of a resistor close to a pure resistance, but may have an inductance component or a capacitance component. Since the fixed impedance circuit 9 generates a large amount of heat due to the bypass current, it is preferable to provide the cooling means 12.

  FIG. 2 is a diagram for explaining an equivalent circuit of the plasma processing apparatus shown in FIG. In the figure, the same parts as those shown in FIG. 9 are denoted by the same reference numerals, and the description thereof is omitted.

In this example, a pure resistor R _SH is used as the fixed impedance circuit 9. By setting the pure resistance value of R _SH than the value of the load impedance Z _LOAD sufficiently small, the load impedance Z _LOAD, the pure resistance R _SH as majority fixed impedance circuit of the power regardless of the fluctuation of the value Will be thrown into.

  Therefore, the voltage Vpp of the stage 6 detected by the voltage sensor 10 is determined by the following equation almost regardless of the plasma state. That is, at the time of plasma processing, a desired voltage Vpp can be supplied to the stage 6 without a time delay until matching by an automatic matching unit is achieved as in the prior art.

Vpp = 2.83 (P · R _SH ) ^1/2
Here, P is the output of the high-frequency voltage generating means 8.

In an etching apparatus for processing the gates of transistors constituting an LSI, the bias voltage applied to the wafer tends to decrease due to the recent thinning of the Poly-Si film. For this reason, about 600V is sufficient as a general value of Vpp. Therefore, if the resistance R _SH is 50Ω and the maximum value of the output P of the high-frequency voltage generation means 8 is 1500 W, the obtained Vpp is 662 V, which is almost sufficient. The output of the high-frequency voltage generation means 8 is required to be higher than the conventional value, but due to recent advances in power transistor technology, the price of the power supply is not proportional to the output, and even a relatively large output power supply has a small output. The cost difference with the power supply is not great.

  The fixed impedance circuit 9 is not limited to a pure resistance, and may have an inductance or a capacitance component. However, in any case, it is desirable to have a certain resistance component from the viewpoint of stabilizing the voltage applied to the stage.

FIG. 3 is a diagram illustrating a case where the fixed impedance circuit 9 includes a resistor R _SH and an inductance L _SH . At this time, in order to efficiently introduce the power to a fixed impedance circuit 9 side, the interior of the fixed matching circuit 11, the capacitance C _MC is required close to the value of resonant inductance L _SH series. The capacitance C _MC as a variable, by finely adjusting, it is possible to adjust the ratio of the current flowing through the fixed impedance circuit 9.

2 and FIG. 3, most of the current flows not on the path from the stage 6 to the processing chamber (earth) via the plasma but on the path to the ground via the fixed impedance circuit 9. Set circuit constants to flow. Thereby, the load side impedance (the parallel impedance of the load impedance Z _LOAD and the fixed impedance circuit 9) viewed from the high frequency voltage generating means 8 becomes substantially constant irrespective of the plasma state, that is, R _PL , C _S1 , C _S2. Thus, the circuit constant of the matching circuit can be almost fixed.

FIG. 4 is a diagram showing a load-side impedance (complex impedance Z = R + jX) viewed from the high-frequency voltage generating means 8 when the pure resistance R _SH is changed and the power consumed by the fixed impedance circuit 9 is changed. .

  As shown in FIG. 4, it can be seen that the greater the power consumed by the fixed impedance circuit 9, the less the load impedance moves with respect to the plasma state. Such characteristics vary depending on the plasma state, the diameter of the wafer that is the object to be processed, and the stage design, but about 50% of the output of the high-frequency voltage generating means 8 is consumed by the fixed impedance circuit 9. As a result, a sufficient effect can be obtained.

When the change in the load side impedance (the load impedance Z _LOAD and the parallel impedance of the fixed impedance circuit 9) is sufficiently small, the output of the voltage sensor 10 is fed back to the high frequency voltage generating means 8 and the detected value of the voltage sensor 10 is By controlling the output value of the voltage generator 8 so as to be constant, the process can be controlled stably and at high speed.

  In other words, in this example, the output of the high-frequency voltage generating means 8 is only feedback controlled by the voltage sensor 10 in response to a predetermined voltage instruction (Vpp), and the stage of the desired voltage Vpp is matched. Can be supplied to. Further, since an automatic matching unit is unnecessary, a desired voltage Vpp can be applied to the stage in the order of 10 ms, and variations in processing results due to the initial matching operation can be eliminated.

  FIG. 5 and FIG. 6 are diagrams for explaining the function and effect of the present invention. FIG. 5 shows the output voltage waveform (a) of the high-frequency voltage generating means 8 and the voltage sensor 10 in the conventional configuration shown in FIG. It is a figure explaining the voltage waveform (b) to do. As shown in FIG. 5, in the conventional configuration, the waveform is distorted due to the difference in the incident characteristics of electrons and ions in the ion sheath to the wafer. In the equivalent circuit shown in FIGS. 2, 3, and 9, the ion sheath is described as a simple capacitor capacity. In practice, however, ions can always enter the wafer from the plasma over one period of high frequency, but the electrons It can enter only for a moment when the wafer voltage becomes the most positive. For this reason, distortion occurs in the waveform. Furthermore, various harmonics are superimposed on the wafer bias voltage waveform depending on the state of the plasma and the configuration of the matching circuit. For this reason, even if it is going to control by peak-to-peak voltage (Vpp), it may be difficult to determine what voltage should be adopted as a peak. In such a case, the Vpp control is less stable than the power control.

FIG. 6 is a diagram for explaining the output voltage waveform (a) of the high-frequency voltage generation means 8 and the voltage waveform (b) detected by the voltage sensor 10 in the configuration of the present embodiment shown in FIG. In the configuration of the present embodiment, as shown in FIG. 6, the load side impedance (the parallel impedance of the load impedance Z _LOAD and the fixed impedance circuit 9) viewed from the high-frequency voltage generating means is close to the pure resistance, so the waveform is almost distorted. Absent. For this reason, if the sine wave voltage (a) is applied by the high frequency voltage generating means 8, the voltage (b) having almost the same waveform can be supplied to the stage. Therefore, the variation in detecting the peak-to-peak voltage is extremely small, and stable plasma processing can be realized.

  FIG. 7 shows the output voltage waveform (a) of the high-frequency voltage generating means 8 and the voltage waveform (b) detected by the voltage sensor 10 when a rectangular wave generating means having a low duty ratio is used as the high-frequency electricity generating means. It is a figure explaining.

Even when a rectangular wave having a low duty ratio as shown in FIG. 7 is generated, a voltage having a waveform close to that can be applied to the stage. At the wafer position, the waveform is slightly distorted by the effect of the inductance L _{ST in} the stage and the capacitance C _ESC between the stage and the wafer. Can do. By giving such a waveform. As shown in the above-mentioned paper (Journal of Appled Physics), the energy distribution of ions can be narrowed, that is, aligned with a certain energy. Also, by narrowing the ion energy, J. Vac. Sci. Technol. B22, p. As shown in the paper by Silapunt et al., It is known that the etching shape, the selectivity with respect to the base and the resist are improved, and the etching performance can be improved.

  As described above, according to the present embodiment, it is possible to realize plasma processing with little variation in processing results. In addition, it is possible to precisely control not only the average value of ion energy but also the distribution of ion energy. In particular, in plasma etching processing, an excellent etching profile with high perpendicularity should be realized for various device applications. Can do. In addition, the overall plasma processing performance and the operating rate of the apparatus are improved, and fine etching processing with high throughput, high-quality film formation processing, surface processing, and the like are possible. The present invention is not limited to the field of manufacturing semiconductor devices, and can be applied to the manufacture of liquid crystal displays, film formation of various materials, and surface treatments.

It is a figure explaining the plasma processing apparatus which concerns on embodiment of this invention. It is a figure explaining the equivalent circuit of the plasma processing apparatus shown in FIG. Is a diagram showing a case where fixed impedance circuit 9 comprises a resistor _{R SH} and the inductance _{L SH.} It is a figure which shows the load side impedance seen from the high frequency voltage generation means 8, when the pure resistance _RSH is changed and the electric power consumed by the fixed impedance circuit 9 is changed. It is a figure explaining the output voltage waveform (a) of the high frequency voltage generation means 8, and the voltage waveform (b) which the voltage sensor 10 detects. It is a figure explaining the output voltage waveform (a) of the high frequency voltage generation means 8, and the voltage waveform (b) which the voltage sensor 10 detects. The figure explaining the output voltage waveform (a) of the high frequency voltage generation means 8 and the voltage waveform (b) detected by the voltage sensor 10 when the rectangular wave generation means having a low duty ratio is used as the high frequency electricity generation means. is there. It is a figure explaining the conventional plasma processing apparatus. It is a figure explaining the equivalent circuit of the plasma processing apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processing chamber 2 Vacuum exhaust means 3 Semiconductor wafer 4 Transfer system 5 Gas inlet 6 Stage 7 Plasma generating means 8 High frequency voltage generating means 9 Fixed impedance circuit 10 Voltage sensor 11 Semi-fixed matching circuit 12 Cooling means 13 Impedance automatic matching device 14 Plasma

Claims (4)

In a plasma processing apparatus comprising a processing gas inlet, a vacuum exhaust means and a stage on which a sample is placed, and converting the introduced processing gas into plasma and subjecting the sample to plasma processing,
High-frequency voltage generation means for accelerating ions incident on the sample by supplying high-frequency power to the stage;
A voltage sensor for detecting a high-frequency voltage supplied to the stage and controlling the high-frequency voltage generating means so that the voltage becomes a set value;
A fixed impedance circuit connected in parallel to the stage and acting as a load of the high-frequency generating means;
The plasma processing apparatus, wherein the impedance of the fixed impedance circuit is set so that the power supplied to the fixed impedance circuit side is 50% or more of the output of the high-frequency voltage generating means. The plasma processing apparatus according to claim 1,
A high-frequency voltage generating means supplies a high-frequency voltage generated through a semi-fixed matching unit capable of finely adjusting impedance to a stage. The plasma processing apparatus according to claim 1,
The plasma processing apparatus, wherein the fixed impedance of the fixed impedance circuit is a resistor having a cooling means. 2. The plasma processing apparatus according to claim 1, wherein the high frequency voltage generating means generates a high frequency pulse voltage.

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