JPH0719770B2 - Plasma processing device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a plasma processing apparatus, and more particularly to a plasma processing apparatus suitable for uniform plasma processing.

[Background of the Invention]

In the conventional plasma processing apparatus, the sample electrode on which the sample is placed is made of a conductive material (for example, aluminum, stainless steel,
(Eg carbon), the surface of the sample electrode is coated or installed with an insulating material.

For example, as described in JP-A-58-213427, by covering the discharge region with a cover made of a material stable in an active reaction gas such as quartz glass, the contamination of the etching sample with reaction products is prevented, There are some which are designed to perform efficient etching.

Further, as described in, for example, Japanese Patent Publication No. 56-53853, a DC circuit is formed by utilizing the electric conductivity of gas plasma by interposing a dielectric film between the sample stage that is forcibly cooled and the material to be processed. Is provided, by applying a potential difference between the sample stage and the substance to be processed, the substance to be processed is strongly adsorbed to the sample stage via the derivative film, and in dry etching using high-frequency glow discharge, It promotes heat transfer between the material to be processed and the sample stage, and further prevents the temperature rise of the resist used as a mask for transferring a fine pattern to the material to be processed, thereby causing thermal deterioration such as deformation or deterioration of the mask. There are things that prevent it.

Further, for example, as described in Japanese Patent Publication No. 55-9464,
In order to improve the speed ratio between the etching rate of silicon on a silicon substrate and the etching rate of silicon oxide on a silicon substrate, a sample table for mounting a sample on an electrode is provided,
There is one in which a fluorine resin is used as the material of the sample table and plasma etching is performed.

However, there is no one provided with an insulating material in order to make the discharge of the electrode portion uniform and perform a uniform plasma treatment.

[Object of the Invention]

An object of the present invention is to provide a plasma processing apparatus capable of uniformizing discharge and obtaining uniform etching or film formation.

[Outline of Invention]

It is known that by using a low frequency, for example, a frequency of 3 MHz or less, the etching rate is increased as compared to the conventionally used etching at 13.56 MHz.
However, at a frequency of 3 MHz or less, a problem that concentrated discharge occurs as shown in FIG.

Therefore, by using a plasma processing apparatus shown in FIG. 5, in this case, an etching apparatus, using a silicon wafer as a material,
An experiment was conducted to investigate the state of discharge by increasing the high frequency power density in the frequency range of 3 MHz or less. In this case, 1 is a sample, a silicon wafer, 2 is a processing chamber, 3 is a sample electrode, 4 is a sample material, 5 is an insulating material, 7 is a high frequency power source, 8 is a matching device, 9 is a counter electrode, 10 is a flow control valve, 11 is an earth shield and 12 is an exhaust port. As the discharge conditions during the experiment, the processing gas was
CHF ₃ gas was 100 SCCM, the pressure was 0.5 Torr, the electrode interval was 50 mm, and the frequency of the high frequency power supply was 1 MHz.

When the high frequency power density was increased to ² w / cm ² or more, several parts of the outer peripheral portion of the silicon wafer 1 with large discharge emission intensity were visually confirmed. Also, when a silicon wafer 1 whose surface is thermally oxidized and patterned by a photoresist (OFPR-800) is used, a portion having a high discharge emission intensity is visually observed at several places on the outer peripheral portion of the silicon wafer 1 as described above. It was confirmed that the resist was altered in spots and the etching rate in the altered portion was increased. The increase in etching rate was about 1.5 times that of the other parts.

Since the surface of the thermally oxidized silicon wafer is mainly etched by the ion effect, the number of ions is increased in the altered portion, or the acceleration energy when the ions are incident on the silicon wafer 1 is increased. It is considered that

As a result of investigating the nonuniformity of this discharge, it was found that there was contact with the sample electrode 3 in the altered portion due to the warp of the silicon wafer 1 itself and the unevenness of the sample holder 4. In order to confirm this, a small piece of 2 × 2 × 0.5t aluminum was placed on the sample electrode 3 under the center of the silicon wafer 1 and discharged under the same conditions as described above. As a result, a portion where the emission intensity of the discharge was high was confirmed on the surface of the center of the silicon wafer on which the small piece of aluminum was placed and on the outer circumference of the electrode.

From this, it was found that the nonuniformity of discharge can be improved by providing an insulating material on the mounting surface of the silicon wafer 1 on the sample electrode 3. Further, even in the discharge using SiH ₄ (monosilane) gas, there is a portion where the emission intensity of the discharge is increased as in the case of the discharge using CHF ₃ gas. We got the prospect that the non-uniformity could be improved.

The present invention provides a processing chamber in which a processing gas is introduced and decompressed and exhausted to a predetermined pressure, a sample electrode provided in the processing chamber for placing a sample, and a counter electrode provided in the processing chamber and facing the sample electrode. The high frequency power applied between the sample electrode and the counter electrode is a high frequency power source that uses power of a frequency of 3 MHz or less at a density of ² w / cm ² or more, and the sample electrode and the sample are prevented from directly contacting each other. It is composed of an insulating film provided on the surface of the sample electrode, the thickness of the insulating film is 2 mm or less, and the film thickness is changed so that it is thickest at the position corresponding to the central portion of the sample and thinnest at the peripheral portion. It is a thing.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows the sample electrode 3 of the plasma processing apparatus shown in FIG.
In the figure showing the details of the parts, the same reference numerals indicate the same members, and the difference between this figure and FIG. 5 is that the sample electrode 3 is covered with the insulating material 6a. Material 6a,
In this case, it is placed on the surface sprayed with alumina (film thickness 200 μm).

When the discharge state was examined under the same conditions as in the experiment using the plasma processing apparatus shown in FIG. 5 with the plasma processing apparatus shown in FIG. 1, the discharge was concentrated even at the maximum high frequency power density of 5 w / cm ² . Did not occur. In addition, the high frequency power density was set to 3w / cm ² and the silicon wafer was thermally oxidized to the photoresist.
Even when the silicon wafer 1 patterned by OFPR-800 (product name of Tokyo Ohka Kogyo Co., Ltd.) was used, neither alteration of the resist nor partial increase in etching rate occurred.

Next, FIG. 2 shows the results of examining the change in the etching rate of the surface of the thermally oxidized silicon wafer 1 by changing the film thickness of the alumina film of the insulating material 6a between 0 and 5 mm. The processing gas is CHF ₃ , the gas flow rate is 100 SCCM, the high frequency power density is 3 w / cm ² ,
The high frequency power frequency was 1 MHz and the pressure was 0.5 Torr. Insulating material 6a is alumina sprayed or alumina plate in this case,
As shown in Fig. 2, when the film thickness is 2 mm,
The etching rate is about 80 compared to when the insulating material 6a is not provided.
%. When the value is decreased below this value, the processing time for processing a certain film thickness increases, and the decrease in the number of processed films per unit time (the decrease in throughput) cannot be ignored. Therefore, the thickness of alumina is preferably 2 mm or less.

Further, as shown in FIG. 2, since the etching rate can be increased or decreased depending on the film thickness of alumina, it is possible to reduce the variation (nonuniformity) in the etching rate of the silicon wafer by adjusting the film thickness of alumina. For example, in this case, the central portion of the silicon wafer 1 has the maximum etching rate, and the following distribution shows a concentric decrease. Therefore, by increasing the thickness of the alumina film to the center of the silicon wafer 1, the etching rate becomes uniform. I was able to improve my sex. In this case, the alumina film has the same effect when the surface of the sample electrode 3 is flattened and the alumina is raised in a convex shape, or when the surface of the sample electrode 3 is processed into a concave shape and the surface of the alumina is flattened.

As described above, according to the present embodiment, by providing the alumina film having the film thickness of 2 mm or less on the sample electrode 3, it is possible to prevent the local discharge that occurs when the etching process is performed by the high frequency power having the frequency of 3 MHz or less, and the local discharge can be prevented. It is possible to prevent deterioration of the resist and increase of etching rate. Further, the discharge can be made uniform by changing the film thickness, and the etching rate can be made uniform over the entire surface of the silicon wafer 1. In addition, since a safe discharge can be obtained for the silicon wafer 1, the etching rate becomes uniform, and the yield is improved. For example, for a silicon wafer having a diameter of 150 mm, the yield is 60% to 90% of that of the conventional wafer. %, And productivity can be increased. In addition, since the quality of the resist can be eliminated, the appearance defect can be eliminated.

Next, a second embodiment of the present invention will be described with reference to FIG.
In this figure, the same symbols as in FIG.
The difference from the figure is that there is a hole in the center of the insulating material 6a in FIG. 1 and the insulating material 6b is provided so as to contact only the peripheral portion of the silicon wafer 1. In this case, the insulating material was provided with a width of 20 mm from the periphery of the silicon wafer 1. When the discharge state in this case was examined under the same conditions as in the above-mentioned one example, discharge concentration did not occur even at the maximum high frequency power density of 5 w / cm ² .

In the second embodiment, as in the case of the first embodiment, local discharge can be prevented, and local deterioration of the resist and increase in etching rate can be eliminated, so that the appearance defect due to the deterioration of the resist can be eliminated. In addition, the etching rate becomes uniform and the yield can be improved.

Next, a third embodiment of the present invention will be described with reference to FIG.
In this figure, the same symbols as in FIG.
The difference from the figure is that the insulating material 6a in FIG.
The insulating material 6c is provided so as to be in partial contact with the back surface of the silicon wafer 1, while the insulating material 6c is provided in a range where the insulating material 6c is in contact with the entire back surface. In this case, the insulating material 6c has a donut shape and is provided at two locations inside and outside the silicon wafer 1 and supports the silicon wafer 1.

According to the third embodiment, the same effect as that of the second embodiment can be obtained, and the deflection at the central portion of the silicon wafer 1 can be suppressed.

The insulating material 6c has a donut shape in this case, but the shape can be arbitrarily selected, and the number of attachments is not limited to two, and two or more or a star-shaped one may be provided. good.

As described above, although alumina is used as the insulating materials 6a to 6c in these examples, BN, SiO, S may be used in addition to alumina.
Even if iN and polytetrafluoroethylene are used, a uniform discharge can be obtained similarly to alumina. When these insulating materials are applied to the sample electrode 3, it is necessary to consider the adhesiveness with the sample electrode 3, the pressure resistance, and the thermoelectric conductivity which influences the wafer cooling effect. In addition, when cooling the wafer, when using helium gas, etc. as a heat medium and putting it in the gap on the back surface of the wafer, consider the sealing structure when attaching the insulating material so that helium gas etc. does not leak into the processing chamber. There is a need to.

Further, in the present embodiment, the case of the etching apparatus was described as the plasma processing apparatus, but the discharge becomes uniform even in the film forming apparatus such as the CVD apparatus, so that the film quality of the film formation on the sample is made uniform. In addition, it is possible to eliminate the appearance defect due to the difference in interference color caused by the difference in film thickness in the related art.

〔The invention's effect〕

According to the present invention, by providing a thin insulating film on the surface of the sample electrode at a position where the thickness is 2 mm or less and this thickness is the largest at the position where the processing speed of the sample is large and the position where the processing speed is small, the sample electrode is opposed to the sample electrode. There is an effect that discharge between the electrodes can be made uniform, and plasma processing for obtaining uniform etching or film formation can be performed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a plasma processing apparatus which is an embodiment of the present invention, FIG. 2 is a graph showing the results of experiments conducted in FIG. 1, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is a sectional view showing a plasma processing apparatus, FIG. 4 is a sectional view showing a plasma processing apparatus which is a third embodiment of the present invention, FIG. 5 is a sectional view showing a plasma processing apparatus which is a conventional example, and FIG. Fifth
It is a graph which shows the experimental result performed by the figure. 1 ... Silicon wafer, 2 ... Processing chamber, 3 ... Sample electrode, 6a to 6c ... Insulating material, 9 ... Counter electrode

Continuation of the front page (72) Yoshinao Kawasaki Inventor Yoshinao Higashitoyoi 794, Higashi-Toyoi, Yamaguchi Prefecture Inside the Kasado Plant, Hitachi Ltd. (56) References JP 59-9173 (JP, A) JP 59- 186325 (JP, A) Japanese Patent Publication Sho 56-53853 (JP, B2)

Claims (1)

[Claims] 1. A processing chamber in which a processing gas is introduced and is evacuated to a predetermined pressure, a sample electrode for arranging a sample in the processing chamber, and a counter electrode provided in the processing chamber and facing the sample electrode. A high-frequency power source that uses power of a frequency of 3 MHz or less at a density of ² w / cm ² or more for the high-frequency power applied between the sample electrode and the counter electrode, so that the sample electrode and the sample do not come into direct contact with each other. It is composed of an insulating film provided on the surface of the sample electrode, and the film thickness of the insulating film is 2 mm or less, and the film thickness is changed so that it is thickest at the position corresponding to the central part of the sample and thinnest at the peripheral part. A plasma processing apparatus characterized by the above.