JPS6310518A - Manufacture of amorphous silicon film - Google Patents

Abstract

PURPOSE:To improve reliability of a device having an a-Si:H film as a photoconductive layer, by interposing a buffer layer between a substrate and the a-Si:H film, a device grade, so that internal stress owned by the a-Si:H film is moderated to prevent peeling, cracking, floating, and the like of the film due to the internal stress from occurring. CONSTITUTION:A buffer layer 5 made of a-Si:H and interposed between a glass substrate 1 and a device-grade (i) layer 2 is made to own internal stress smaller than the (i) layer 2. Therefore the buffer layer 5 is hard to be peeled from the substrate 1. Another role of the buffer layer 5 is that this film is hard to be peeled due to thermal stress because the value of its thermal expansion factor is near to that of the glass substrate 1 rather than that of the (i) layer 2. The buffer layer 5 is formed in the following conditions; the substrate temperature increases, or SiH4-gas pressure decreases respectively at the time of film formation as the positions of layers become more distant from the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for manufacturing an amorphous silicon (hereinafter referred to as a-8i) film that relieves the internal stress of the film.

(Prior art) Fig. 2 shows a photoconductive layer formed on a glass substrate 1 made of quartz, Pi1.
(hereinafter also simply referred to as an i-layer) 2, and an n0 omic contact layer 3. in which the electrode lead portion is doped with phosphorus (P). A1. This figure shows the structure of a typical coplanar photocell in which metal electrodes 4 made of Cr or the like are sequentially laminated. A (device grade) non-doped a-Si:H film with a high photoconductivity layer like this conventional example has a compressive internal stress in the film of the magnitude of 10@~1 G'' dynes/d. (J, J, A, P, 22, 5.167 (1
9113) K., QZAIA et al.).

For example, as shown in Figure 3, the light guiding strength is 1O-6 (Ω
-' Ql -' ) or more, the internal stress of the film is 2 to 4.
XIO' dyne/d is large.Here, compression type refers to a state in which the film tries to stretch.If the internal stress of the film is large,
If the adhesion between the film and the substrate is weak, the film may peel off from the substrate or wrinkle.

As an attempt to reduce the stress in the a-5i:H film, the stress was controlled by the mixing ratio of SiH4 gas as a raw material gas and 5i2H gas.

A laminated structure of an SL, H, film (low stress) and a SiH4 film (high stress) has been reported (see '85 Autumn Science Proceedings, p721.3p-ZA-16), and the former has a strong odor. The latter has the drawback of deterioration of the photoconductive properties of a-8il[l by SL, H, and gas;

Characteristic deterioration due to gas mixture due to switching of gas types,
There are problems with reproducibility.

(Objective of the Invention) The present invention solves the problems of the prior art described above, and by providing a buffer layer between the substrate and the a-Si:H film (i-layer), the internal stress of the i-layer can be reduced. The purpose of the present invention is to provide a method for manufacturing an a-3L film in which the

(Structure of the invention) In order to achieve the above object, by plasma CVD method,
At least two layers of a-S i:H films are laminated on a glass substrate, and the film formation conditions are such that the substrate temperature during film formation increases sequentially from layers closer to the substrate to layers farther from the substrate. Alternatively, the pressure of SiH and gas during film formation may be gradually lowered from the layer closer to the substrate to the layer farther from the substrate, or both may be used in combination.

According to this configuration, a buffer layer is interposed between the substrate and the device-grade i-layer, which relieves the internal stress of the i-layer and prevents peeling, cracking, and lifting of the film.

(Example) Hereinafter, embodiments will be described in detail based on the drawings.

FIG. 1 shows one embodiment of the present invention, and the same reference numerals as in FIG.
It was provided between a glass substrate 1 and a device grade layer 2. a-5i: A buffer layer made of H.

This buffer layer 5 has a smaller internal stress than the first layer 2. Therefore, peeling between the substrate 1 and the buffer layer 5 is difficult to occur. Another role of the buffer layer 5 is to control its coefficient of thermal expansion. Since the coefficient of thermal expansion is closer to that of the glass substrate 1 than that of the single layer 2, peeling of the film due to thermal stress is less likely to occur.

The thermal expansion coefficient of Pyrex board is 3.3X10-'/'
C, the thermal expansion coefficient of non-doped a-Si:H film is 1.2
X10-'/'C, whereas that of the buffer layer can be 1.9 to 2.8 X10-'/'C (depending on film formation conditions).

The characteristics of the film formation conditions for the buffer layer 5 are: (1) increasing the S i H gas pressure compared to the device grade 1 layer 2, or (2) lowering the substrate temperature compared to the 1 layer 2. , FIG. 4 shows SiH.

This shows the relationship between gas pressure and the internal stress of the membrane.
Further, FIG. 5 shows the relationship between the substrate temperature and the internal stress of the film. From these figures, it can be seen that the higher the gas pressure and the lower the substrate temperature, the smaller the internal stress of the compression mold.

What is the evaluation of the adhesion between the a-Si:H film and the glass substrate?

There is a method of scratching the a-Si:H film with a metal needle and determining the width of the scratch. The smaller the width of this scratch, the greater the adhesion force.In the case of a conventional single layer a-Si:H film, the width of this scratch is quite large at 10 to 50 mm, but with the structure of the present invention, the width of the scratch is less than Loom. It is. (The width value depends on the thickness of the metal needle used, but can be used to assess relative adhesion).

In the device manufacturing wet process, a-
The failure of Si:H film peeling occurs when the width of the scratch is 3
This was the case when the diameter was 5 mm or more. Therefore, in the conventional method, failures such as peeling of the a-Si:H film sometimes occurred during the process, but with the structure of the present invention, such problems have been completely eliminated.

Next, specific manufacturing conditions for the first layer 2 and the buffer layer 5 will be explained. First, a-Si:H is deposited on a glass substrate on the ground side by a capacitively coupled RF glow discharge method.

The device grade film formation conditions for layer 1 and 2 are substrate temperature;
60-300°C, RF power: 10-40W.

SiH, gas pressure: 0.07 to 0.2 Torr, gas flow rate: 5 to 303 ccIm, and electrode spacing: 36 mm. The film thickness is preferably 8,000 to 12,000 people.

The film-forming conditions for the buffer layer 5 are: substrate temperature; 140-200;
°C, RF power: 10-40W, SiH, gas pressure: 0
．． 2S~0.4Torr, gas flow rate; 5~303cc1
1, and the film thickness is preferably 100 to 2000 people.

Among the conditions for forming the buffer layer above, the substrate temperature and SiH4
The gas pressure only needs to meet this condition for one of them, and the other conditions may be the same as those for layer 1 and layer 2.

For example, when forming a buffer layer by changing only the substrate temperature, first, the substrate temperature is 200°C, the RF power is 20W,
5i) Reduce I4 pressure to 0. ITorr, gas flow rate 30sc
A buffer layer of about 2,000 layers is formed by plasma discharge. Then, stop the plasma discharge.

While the SiH gas is flowing, the pressure is reduced to 0. Keep IT'orr.

Raise the substrate temperature to 290°C. Then, plasma discharge is started again to form an i-layer with a thickness of approximately 100 mm.

(Effects of the Invention) As explained above, according to the present invention, by providing a buffer layer between the substrate and the device-grade a-Si:H film, the internal stress of the a-Si:H film can be reduced. It is possible to prevent the film from peeling off, cracking, floating, etc. due to internal stress, thereby increasing the reliability of devices using the a-8L:H film as a photoconductive layer.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a sectional view of a conventional example, and FIG. 3 is a diagram showing the relationship between the photoconductive layer and internal stress of an a-Si:H film. , FIG. 4 is a diagram showing the relationship between SiH4 gas pressure and internal stress, and FIG. 5 is a diagram showing the relationship between substrate temperature and internal stress. 1...Glass substrate, 2...Non-doped a-
Si:H film (i layer), 3... Ohmic contact layer, 4... Metal electrode, 5... Buffer layer. Patent applicant Ricoh Co., Ltd. Fig. 1 Fig. 2 1. Force 1 Laser shake 2-a-SiHMl (I-layer arm) 3...Ohmic contact layer 4...&-5I4LyII 5 ・Buffer ・1 3rd Figure 4 Figure 5 Basic set-X and-

Claims (1)

[Claims] At least two layers of a-Si:H film are laminated on an insulating substrate such as glass by a plasma CVD method, and the film forming conditions are set to any one of the conditions shown below. A method for producing an amorphous silicon film characterized by the following characteristics. Condition 1: The at least two a-Si:H films are formed such that the substrate temperature during film formation increases sequentially from layers closer to the substrate to layers farther from the substrate. Condition 2 SiH when forming the at least two layers of a-Si:H film
_4 To form a layer in which the gas pressure gradually decreases from the layer closer to the substrate to the layer farther from the substrate. Condition 3: The at least two layers of a-Si:H films are formed such that the substrate temperature increases sequentially from the layer closer to the substrate to the layer farther from the substrate, and the SiH_4 gas pressure decreases sequentially. .