JPH05335244A - Forming method for amorphous silicon thin film - Google Patents

Abstract

PURPOSE:To form a film of necessary thickness in a short time while obtaining film quality by forming the film by a continuous discharge at the initial of forming by a plasma CVD method, and then forming it to a necessary thickness by an intermittent discharge. CONSTITUTION:A high frequency power source 11 is operated to apply a continuous high-frequency power 15 between a high-frequency electrode 2 and a ground electrode 3, the electrodes are continuously discharged therebetween, and an amorphous silicon thin film is formed on a rear surface of a substrate 4. The high frequency power is so set to 100W as not to generate particles. After the continuous discharge of 10min is finished, a waveform shaper 13 is operated, an output of the power source 11 is varied to an amplitude-modulation high frequency power 16, an intermittent discharge is generated between the electrodes 2 and 3 to continue the formation of the film. Thus, a film forming time can be significantly shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an amorphous silicon thin film on the surface of a substrate by the plasma CVD method.

[0002]

2. Description of the Related Art Conventionally, in a film forming chamber (vacuum chamber), silane gas (SiH ₄ ) and hydrogen gas (H
A substrate supported by one electrode of the counter electrode by introducing the source gas of ₂ ) and applying high-frequency power between the counter electrodes to form plasma by discharge, and exciting and decomposing the source gas with the plasma. There is known a film forming method by a plasma CVD method in which an amorphous silicon thin film is formed on the surface of the. Thin film transistor (TFT)
It has been applied to the manufacture of semiconductor devices such as.

The discharge between the opposing electrodes includes continuous discharge and intermittent discharge.

The continuous discharge is a commonly used plasma CVD method, and has a characteristic that a high quality amorphous silicon thin film can be formed at a low substrate temperature.

The intermittent discharge has the same basic film forming conditions (pressure, temperature, raw material gas) as in the case of the continuous discharge, but the high frequency power applied to the counter electrode is the high frequency power amplitude-modulated. The method proposed by Watanabe et al. Of Kyushu University after 1987 (Y. Watanab).
e et al. Appl. Phys. Let
t. 53, 1263 (1988), Watanabe et al. Kyushu University Engineering Bulletin 60, No. 6, 739 (1987), Shiratani et al. Kyushu University Engineering Bulletin 62, No. 6, 677 (1989), Shiratani et al. Plasma Research Society Document EP-89-62
(1989)). It is said that the film formation rate can be improved and the particles generated in the gas phase can be reduced as compared with the case of continuous discharge.

[0006]

The conventional amorphous silicon film forming method as described above has the following problems.

That is, in the case of continuous discharge, when the high frequency power is increased or the amount of the raw material gas introduced is increased to increase the film formation rate, the reaction in the gas phase is promoted and the generation of particles occurs. In addition, a large amount of SiH ₂ radicals are generated in plasma, resulting in poor film quality. Therefore, in order to obtain a film quality that can be practically used, the film formation speed must be slowed down, the film formation time becomes longer, and the efficiency decreases (for reference, Akihisa Matsuda Electronics Technology General Institute Research Report 864
No. P35-45, A.I. Matsuda and N.M.
Hata Glow-Discharge Hydro
Generated Amorphous Silico
n, edited by K.N. Tanaka P28
(1989) and the like. ).

On the other hand, the intermittent discharge method can improve the film formation rate and reduce particles as described above, but has a problem that the film quality as a semiconductor material is inferior to that in the case of continuous discharge. there were.

[0009]

The present invention has been made in view of the problems as described above, and it is possible to secure the film quality as a semiconductor material and to reduce the film thickness required in manufacturing a semiconductor device. It is an object to provide a method for forming a film in a short time.

The amorphous silicon thin film forming method of the present invention which achieves the above object is a method of forming an amorphous silicon thin film on the surface of a substrate by a plasma CVD method. The feature is that the film is formed to a required film thickness by intermittent discharge.

Needless to say, the amount of high-frequency power and the amount of raw material gas introduced in the continuous discharge are set so that particles are not generated in the film forming chamber.

Film formation by continuous discharge and intermittent discharge may be carried out in the same film forming chamber or in another film forming chamber.

The frequency of the high frequency power is 1 kHz to 100 M
Hz (typically 13.56 MHz). In continuous discharge, such high-frequency power is applied continuously in time, whereas in intermittent discharge, 100 Hz to 100 k
Modulate at Hz and apply. The duty ratio, which is the ratio of the discharge time at the time of modulated discharge, can be 1% or more and less than 100%.

[0014]

According to the method for forming an amorphous silicon thin film of the present invention, amorphous silicon having a good film quality is formed by continuous discharge at the initial stage of film formation, and particles are formed by the intermittent discharge after that. Without any occurrence
Amorphous silicon can be deposited at a high speed, and the time required for the required film thickness can be shortened.

In a semiconductor device such as a thin film transistor, the amorphous silicon layer is theoretically 10 to 20 nm as a semiconductor material, and physically 50 to 100 nm.
Is sufficient, and the remaining amorphous silicon layer is used as a current path or an etching margin. Therefore, even if the film quality of this part is slightly inferior, there is no problem in device performance.

Therefore, of the amorphous silicon layer having a required film thickness, a portion requiring a film quality as a semiconductor material is formed by continuous discharge, and then the remaining film thickness portion is formed by intermittent discharge. The film time can be shortened.

[0017]

[Example] In manufacturing a thin film transistor, a film thickness of 300
nm amorphous silicon thin film was formed.

FIG. 1 shows the construction of the apparatus used. The high-frequency electrode 2 and the ground electrode 3 are installed in the vacuum container 1 so as to face each other so that the substrate 4 can be supported by the ground electrode 3 and the matching circuit 12 is provided in the high-frequency electrode 2.
The high frequency power source 11 is connected via. High frequency power supply 1
The waveform generator 13 is connected to the waveform generator 1.
The continuous high frequency power 15 can be changed to the amplitude modulation high frequency power 16 by the modulation signal 14 of.

A gas introduction system for introducing a raw material gas 5 such as SiH ₄ and H ₂ through a flow rate controller 6 is connected to the vacuum container 1, and an exhaust system 9 is connected through a variable conductance valve 8. The inside of the vacuum container 1 can be adjusted to a predetermined pressure. The pressure inside the vacuum container 1 is measured by a pressure gauge 7.

A substrate heating mechanism 10 is built in the ground electrode 3 so that the substrate 4 can be heated.

Reference numeral 17 in the figure represents plasma formed by the discharge between the high frequency electrode 2 and the ground electrode 3.

An amorphous silicon thin film having a thickness of 300 nm was formed on the surface of the substrate 4 by using the film forming apparatus having the above structure.

First, after mounting the substrate 4 on the ground electrode 3,
The vacuum chamber 1 is evacuated to a vacuum, sufficient vacuum (5 × 10 ^-3
After obtaining Pa (3.8 × 10 ⁻⁵ Torr), the substrate 4 is heated (250 ° C.), the raw material gas 5 is introduced, and the pressure inside the vacuum container 1 is adjusted to 100 Pa (0.75 Torr). did. The pressure is adjusted by the flow rate controller 6 and the variable conductance valve 8. The raw material gas 5 is a mixture of SiH ₄ gas and H ₂ gas (composition ratio 1: 4), and is made to have a particle size of 50 so as not to generate particles during film formation by continuous discharge.
The flow rate was 0 sccm.

Next, the high-frequency power source 11 is operated to apply continuous high-frequency power 15 between the high-frequency electrode 2 and the ground electrode 3 to continuously discharge between both electrodes to form an amorphous silicon thin film on the surface of the substrate 4. Filmed The high frequency power was 100 w (0.1 kw) so that particles would not be generated.

The film formation rate of the amorphous silicon thin film obtained under the above conditions is about 10 nm / min,
An amorphous silicon thin film having a film thickness of about 100 nm was formed with a film forming time of 10 minutes.

After the continuous discharge for 10 minutes is completed, the waveform shaper 13 is operated to change the output of the high frequency power source 11 to the amplitude modulation high frequency power 16 so that the intermittent discharge is generated between the high frequency electrode 2 and the ground electrode 3. Film formation was continued so that it would occur.
The frequency of the modulation signal 14 was 500 Hz, and the duty ratio was 50%.

The film formation rate of the amorphous silicon thin film obtained under the conditions of this intermittent discharge is about 86 nm / min, and the amorphous silicon thin film with a film thickness of 200 nm is formed with the film forming time of 2.3 minutes. An amorphous silicon thin film having a film thickness of 300 nm was formed on the surface of the substrate 4. Total film formation time is 12.3 minutes, 300n only with continuous discharge
It could be about 1/3 of the time (30 minutes) for forming a film having a thickness of m.

Table 1 shows the characteristics of the amorphous silicon thin film formed by continuous discharge and the amorphous silicon thin film formed by intermittent discharge.

[0029]

[Table 1]

Electric conductivity ratio of amorphous silicon thin film formed by intermittent discharge (photoelectric conductivity / dark electric conductivity)
Is smaller than the electric conductivity ratio of the amorphous silicon thin film formed by continuous discharge.

As described above, the film forming rate is 8.6 times higher in the case of intermittent discharge than in the case of continuous discharge.

FIG. 2 is a diagram showing a result of infrared spectroscopic measurement of the amorphous silicon thin film. In addition, FIG. 3 shows the result of peak separation of the waveform near the wave number of 2000 cm ⁻¹ indicating the Si—Hx bond. In each figure, (a) is an amorphous silicon thin film by intermittent discharge, and (b) is an amorphous silicon thin film by continuous discharge.

In the amorphous silicon thin film formed by the intermittent discharge, the peak showing the bond between silicon and hydrogen is divided into two and contains many Si--H ₂ bonds, and the film quality as a semiconductor material is inferior. The amorphous silicon thin film formed by continuous discharge had only one peak showing the bond between silicon and hydrogen, and showed that only Si—H bond was contained, and the film quality was good.

In the amorphous silicon thin film in the thin film transistor, the film thickness as a semiconductor material is required to be 10 to 20 nm, and the rest is a current path or an etching margin area. Therefore, there is no problem in terms of the performance of the semiconductor device even if the region where the film quality as the semiconductor material is required is formed by continuous discharge and the remaining part is formed as an amorphous silicon thin film by the intermittent discharge with poor film quality as in the embodiment. As a result, the film formation time of the amorphous silicon thin film can be significantly shortened.

[0035]

According to the present invention, there is an effect that the film forming time can be greatly shortened, and the manufacturing efficiency of semiconductor devices can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a film forming apparatus used in an embodiment of the present invention.

FIG. 2 is a graph of infrared spectroscopic analysis of an amorphous silicon thin film.

FIG. 3 is an enlarged graph of a portion showing a bond between silicon and hydrogen in infrared spectroscopy.

[Explanation of symbols]

 1 Vacuum Container 2 High Frequency Electrode 3 Ground Electrode 4 Substrate 5 Raw Material Gas 6 Flow Controller 7 Pressure Gauge 8 Variable Conductance Valve 9 Exhaust System 10 Substrate Heating Mechanism 11 High Frequency Power Supply 12 Matching Circuit 13 Waveform Generator 14 Modulation Signal 15 Continuous High Frequency Power 16 Amplitude modulation high frequency power

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[Procedure amendment]

[Submission date] July 9, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction content]

Among the basic film forming conditions, the intermittent discharge is
The temperature and the kind of the raw material gas are the same as in the case of the continuous discharge, but the pressure and the flow rate of the raw material gas are the same as those in the case of the continuous discharge.
It may be the same or different. The intermittent discharge is a method in which the high frequency power applied to the counter electrode is a high frequency power that is amplitude-modulated, and has been proposed by Watanabe et al. Of Kyushu University since 1987 (Y. Watanabe e.
t al. Appl. Phys. Lett. 53,
1263 (1988), Watanabe et al. Kyushu University Bulletin of Engineering 60th
Volume 6, No. 739 (1987), Shiratani et al. Kyushu University Bulletin of Engineering Vol. 62, No. 6, 677 (1989), Shiratani et al. Plasma Research Society Material EP-89-62 (198)
9)). It is said that the film formation rate can be improved and the particles generated in the gas phase can be reduced as compared with the case of continuous discharge.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

According to the method for forming an amorphous silicon thin film of the present invention, amorphous silicon having good film quality is formed by continuous discharge at the initial stage of film formation, and particles are formed by intermittent discharge after that. It is possible to reduce the time required to form an amorphous silicon film at a high speed and to form a film having a necessary film thickness without causing any generation.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction content]

Next, the high-frequency power supply 11 is operated to apply continuous high-frequency power 15 between the high-frequency electrode 2 and the ground electrode 3 to continuously discharge between both electrodes, and an amorphous silicon thin film is formed on the surface of the substrate 4. Filmed As the particles does not occur, the high-frequency power was 100 W (0.1k W).

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (2)

[Claims] 1. A method of forming an amorphous silicon thin film on a surface of a substrate by a plasma CVD method, characterized in that the film is formed by continuous discharge at the initial stage of film formation, and then formed by intermittent discharge to a required film thickness. Method for forming amorphous silicon thin film. 2. The film formation by continuous discharge and intermittent discharge comprises:
The method for forming an amorphous silicon thin film according to claim 1, wherein the method is performed in the same chamber or another chamber.