JPS61117823A - Plasma cvd apparatus - Google Patents

Abstract

PURPOSE:To enable high quality and high yield to be obtained by improving the gas utilization factor by a method wherein the raw material gas introduced into a vacuum reaction layer is passed through a cathode made of stainless mesh. CONSTITUTION:The cathode 4 is made of a porous material having fine holes, through which the raw material gas can be passed, such as stainless mesh, and an earth shield 5 of the back of the cathode 4 is provided with an opening 11. A gas exhaust port 9 is formed by installing an exhaust pipe 12 leading out of the bath to this opening 11. The raw material gas introduced into the vacuum reaction bath 1 through a raw material gas supply port 8 is exhausted out of the bath through the cathode 4. This construction allows the raw material gas introduced into the bath to necessarily pass through a plasma decomposition area, much improving the film production speed and increasing the gas utilization factor. Besides, under the condition of a sufficient amount of supplied gas, photoelectric conductivity much increases, and high-quality films can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvement of a plasma CVD apparatus, and more specifically, the present invention relates to improvement of a plasma CVD apparatus. The present invention relates to a plasma CVD apparatus in which the plasma is discharged through the tank and discharged to the outside of the tank.

Ryoho J and Skin 1 In recent years, plasma CVD methods have been widely used in semiconductor manufacturing factories, particularly for forming films of amorphous semiconductors, such as amorphous silicon semiconductors.

Conventionally, this plasma CVD method has been used, for example, as shown in FIGS. 2 and 3.
This was carried out using the equipment shown in the figure. In the plasma CVD apparatus shown in FIG. 2, a raw material gas supply hole 8 is formed on one side of a vacuum chamber 1, and a gas exhaust port 9 is provided on the opposite side, so that raw material gases such as silane (SiH4) and disilane (SizH6) are The gas flows from the gas supply hole 8 of the vacuum chamber 1 to the gas discharge port 9 between the anode electrode (sample electrode or upper electrode) 2 and the cathode electrode (lower electrode) 4 which are arranged opposite to each other inside the vacuum chamber. A sample such as an amorphous semiconductor is formed into a film on a substrate 3 that is supplied and attached to an anode electrode 2. A voltage of an appropriate frequency is applied to the cathode electrode 4 from a high frequency power source 7, and a plasma decomposition region is formed between the 7 made electrodes 2, decomposing the raw material gas and dissolving the substrate 3.
Samples such as amorphous semiconductors are formed into films. still,
An earth shield 5 is provided on the back surface of the cathode electrode (lower electrode) 4 (the surface opposite to the surface facing the anode electrode).

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In the plasma CVD apparatus with the above configuration, the raw material gas introduced from the supply hole 8 passes between the opposing electrodes and is discharged from the exhaust port 9, but the plasma decomposition region is not formed in the entire space inside the vacuum chamber, and the anode It is formed only in the space between the electrode and the cathode electrode, and a considerable portion of the raw material gas is exhausted without passing through the plasma decomposition zone, resulting in an extremely low gas utilization rate.

For this reason, a plasma CVD apparatus shown in FIG. 3 was proposed. In this plasma CVD apparatus, the front surface 4a of the cathode electrode 4 (the surface facing the anode electrode) is formed of a stainless steel mesh having a large number of holes, and a gas supply pipe 10 is attached to the rear surface of the cathode electrode 4 to supply the gas. Raw material gas is introduced from the inlet of the supply pipe IO, that is, the gas supply hole 8. The source gas passes through the mesh 4a of the cathode electrode 4,
The raw material gas is configured to flow to a gas outlet 9 formed perpendicularly to the flow direction of the raw material gas, so that most of the raw material gas passes through the plasma decomposition zone. In this plasma CVD apparatus, the high frequency power source 7 is connected to a gas supply pipe 10, and a predetermined high frequency voltage is supplied to the cathode electrode 4 via this gas supply pipe 10.

According to the plasma CVD apparatus having the configuration shown in FIG. 3 above,
Although the gas utilization rate is improved, the powder formed on the cathode electrode is rolled up by the introduced raw material gas, causing pinholes etc. in the sample formed on the substrate 3, which deteriorates the quality of the sample and reduces the yield. There were some drawbacks.

As described above, conventional plasma CVD apparatuses have the drawbacks of low gas utilization rates, or those with improved gas utilization rates have the disadvantages of poor quality and poor yields. A plasma CVD device with high quality and high yield has been long-awaited.

Therefore, an object of the present invention is to use a mesh electrode made of stainless steel as the cathode electrode to which a high frequency voltage is applied, so that the raw material gas introduced into the vacuum reaction tank is passed through the cathode electrode and then removed from the tank. It is an object of the present invention to provide a plasma CVD apparatus which improves the gas utilization rate and improves the quality and yield.

. The above objectives are achieved by the present invention. In summary, the present invention comprises a vacuum reaction tank having a raw material gas supply hole, an anode electrode and a cathode electrode arranged oppositely in the vacuum reaction tank, and a high frequency power source that applies a predetermined high frequency voltage to the cathode electrode. In the plasma CVD apparatus, the cathode electrode is formed of a conductive metal mesh through which the raw material gas can pass, and a ground shield located on the opposite side of the cathode electrode from the anode electrode is used to prevent gas exhaust reaching the outside of the tank. This plasma CVD apparatus is characterized in that a discharge prevention sheet is interposed between the cathode electrode and the earth shield, the sheet forming an outlet and having a large number of pores through which source gas can pass, between the cathode electrode and the earth shield.

According to a preferred embodiment of the present invention, the discharge prevention sheet has a three-layer sandwich structure consisting of a stainless steel mesh, a fluororesin sheet having a large number of pores, and a stainless steel mesh.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a plasma CVD apparatus according to the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 1, the plasma CVD apparatus according to the present invention has a raw material gas supply hole 8 on one side of a vacuum reaction tank 1, and inside the tank, a pair of opposing anode electrodes 2 and a cathode electrode 4 are arranged at the top. and installed at a predetermined position at the bottom. In the plasma CVD apparatus of the present invention, a substrate 3 is attached to the upper anode electrode 2 and a predetermined high frequency voltage is supplied from a high frequency power source 7 to the lower cathode electrode 4. The earth shield 5 on the back side of the cathode electrode 4 has an opening 1
1 is formed. An exhaust pipe 12 reaching the outside of the tank is attached to this opening 11 by, for example, welding (to form a waste gas exhaust port 9).

With this configuration, the raw material gas introduced into the vacuum reaction tank through the raw material gas supply hole 8 provided on one side of the vacuum reaction tank 1 is discharged to the outside of the tank through the cathode electrode 4. be done.

Further, in order to prevent abnormal discharge from occurring between the cathode electrode 4 and the earth shield 5, a discharge prevention sheet 6 through which the raw material gas can pass is arranged between the cathode electrode 4 and the earth shield 5. The discharge prevention sheet 6 preferably has a three-layer sandwich structure consisting of a stainless steel mesh, a fluororesin sheet for accommodating a large number of pores, and a stainless steel mesh. The cathode electrode 4 and the stainless steel mesh of the sheet 6 have pores that do not allow the particles to pass through, and the opening diameter will be 40 lm or less. In this example, the cathode electrode 4 is manufactured by Flowwell Co., Ltd. (Poremet: trade name) with an opening diameter of 20 gm, and the sheet 6 is made by Taiyo Wire Mesh Co., Ltd. (MESH-
30 (trade name) with an opening diameter of 30 gm was used. Further, the fluororesin sheet is not limited to this, and any sheet can be used as long as it is heat resistant and has an insulating property that does not generate gas in a vacuum.

1 凰1 7752A sample was formed on a substrate 3 using the conventional apparatus shown in Fig. 1 and the apparatus of the present invention shown in Fig. 1, and the performance of the re-apparatus was compared.
The distance between the electrodes is 30 mm, and the frequency of the high frequency power source is 13.5.
6MHz, Tempax ψ glass was used as the substrate 3, the substrate temperature was 270°C, and the film thickness produced was 0.40°C.
-0.60. It was wm.

Example 1 Using 100% of 5iH4 as the raw material gas, the flow rate was 110
The pressure was kept constant at 5 ec and 100 millitorr, and the power from the high frequency power source 7 was varied from 4 W to 40 W. First, when the input power was 4 W, the gas decomposition rate was low and in the reaction rate-limiting region, so as shown in FIG. 4, there was no difference in the film forming rate with the re-apparatus. still.

In Fig. 4, the dotted line connecting the Δ points shows the performance of the device of the present invention, and the solid line connecting the 0 points shows the characteristics of the conventional device.As the high frequency power is increased to LOW and 40W, it reaches the flow restriction region. Therefore, the film forming rate was higher with the apparatus of the present invention. At the same time as the film forming rate, both light and dark electrical conductivity and optical forbidden band width were measured, and the results were as shown in FIG. As is clear from Fig. 4, the dark electrical conductivity was almost the same with the sample film prepared using the re-apparatus, but the photoelectric conductivity was 2 to 3 times higher for the sample film prepared using the apparatus of the present invention. It was found that a high quality membrane could be obtained. The optical zonal radiation was the same for all membranes at approximately 1.72 electron volts. The photoelectric conductivity was measured using a He-Ne laser, 632.8 nm, O; 6 mW/c light source.

Example 2 100% 5fzH6 (disilane) was used as the raw material gas, the flow rate was kept constant at 53 CCM, the pressure was kept constant at 500 mTorr, and the measurement was performed at an input power of 40 W. Other conditions are the same as in Example 1.

The film forming speed was 8.2 persons/second in the case of the conventional apparatus, whereas it was 9.2 persons/second in the apparatus of the present invention, which was a considerable improvement. Therefore, it was found that the apparatus of the present invention is effective even when disilane gas is used. Further, in the conventional device, the film thickness on the substrate tended to be non-uniform, but in the device of the present invention, the film thickness was uniform.

Example 3 A gas with a ratio of S i H4:H2 of 1:9 was used as the raw material gas, a total flow rate of 50 SCCM, a constant reaction pressure of 2 Torr, and an input power of 40 W were used.Other conditions were the same as in Example 1 above. and 2.

Under these conditions, the reaction rate was in the rate-determining region, and the film forming rate was the same at 4.0 s/sec for both devices. However, the photoelectric conductivity of the film was 3.9×10-6/Ω am when using the conventional device, whereas it was 5 when using the device of the present invention.
．． A considerable improvement of 0x10-6/Ω-cm was observed, indicating that the apparatus of the present invention is effective even under conditions where the amount of gas supplied is sufficient.

11 Standing J As mentioned above, in the present invention, the cathode electrode 4 is a mesh electrode made of stainless steel, and an opening is formed in the earth shield 5 on the back side of the cathode electrode 4 to form a discharge port reaching the outside of the tank. Since the raw material gas introduced into the tank is configured to pass through the cathode electrode 4 and discharged to the outside of the tank, the raw material gas introduced into the tank will inevitably pass through the plasma decomposition zone, and the above implementation As demonstrated in Examples 1 and 2, the deposition rate is further increased and the gas utilization rate is significantly higher.

In addition, under conditions where the amount of gas supplied is sufficient as in Example 3, the film formation rate is the same, but the photoelectric conductivity becomes even higher, resulting in a high quality film that cannot be obtained with conventional equipment. will be produced.

The photoelectric conductivity was improved in other examples as well, and it can be seen that the performance of the device of the present invention is very excellent. Therefore, there is a remarkable advantage that the yield is improved and that sample films of high quality polycrystalline and equiamorphous semiconductors can be efficiently formed. The possibility of abnormal discharge between the electrode and the earth shield can be easily prevented by using the stainless steel mesh, the fluororesin sheet with many pores, and the stainless steel mesh sheet 6, which has a 3-inch structure, so the overall structure of the device is not complicated. There is no equivalent problem in both cost and manufacturing.

The above embodiments are merely illustrative of the present invention, and it goes without saying that various modifications and changes can be made as necessary.For example, the cathode electrode may be entirely made of stainless steel mesh or may be made of stainless steel. A mesh made of other conductive metals may also be used, and the discharge prevention sheet is not limited to the structure of the embodiment as long as it can prevent discharge and allow raw material gas to pass through.

In addition, 100% silane and 100% disilane are used as raw material gas.
Although an example is shown in which a gas with a ratio of silane to hydrogen of 1:9 is used, the apparatus of the present invention can also be used with other raw material gases for forming a film on a substrate by the plasma CVD method, and similar effects can be obtained. Needless to say, you can get it.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a plasma CVD apparatus according to the present invention. FIGS. 2 and 3 are schematic configuration diagrams illustrating conventional plasma CVD apparatuses, respectively. FIG. 4 is a characteristic diagram comparing the performance of the device according to the present invention and the conventional device shown in FIG. l: Vacuum reaction tank 2 Near-sode electrode 3: Substrate 4: Cathode electrode 5: Earth shield 6: Discharge prevention sheet 7: High-frequency power supply 8: Raw material gas supply hole 9: Gas discharge port

Claims (6)

[Claims] (1) Plasma CVD comprising a vacuum reaction tank having a raw material gas supply hole, an anode electrode and a cathode electrode arranged oppositely in the vacuum reaction tank, and a high frequency power source that applies a predetermined high frequency voltage to the cathode electrode. In the apparatus, the cathode electrode is formed of a conductive metal mesh through which the raw material gas can pass, and a gas discharge port reaching the outside of the tank is formed in the earth shield located on the opposite side of the cathode electrode from the anode electrode. A plasma CVD apparatus characterized in that a discharge prevention sheet having a large number of pores through which source gas can pass is interposed between the cathode electrode and the earth shield. (2) The plasma CVD apparatus according to claim 1, wherein the mesh of the cathode electrode is a stainless steel mesh with an opening diameter of 40 μm or less. (3) The plasma CVD apparatus according to claim 1 or 2, wherein the discharge prevention sheet has a three-layer sandwich structure of a stainless steel mesh, a fluororesin sheet having many pores, and a stainless steel mesh. (4) The plasma CVD apparatus according to claim 1, wherein the source gas is silane (SiH_4). (5) The plasma CVD apparatus according to claim 1, wherein the source gas is disilane (Si_2H_6). (6) Raw material gas is silane (SiH_4) 1: hydrogen (H_
2) The plasma CVD apparatus according to claim 1, wherein the mixed gas is 9.