JPH0483872A - Production of crystalline silicon film - Google Patents

Abstract

PURPOSE:To form a crystalline silicon thin film having large grain size on a glass substrate at a low temp. by specifying the pressure ratio of hydrogen gas to reaction pressure in the process of forming plasma of hydrogen and the reaction gas containing silicon by use of high frequency excited plasma. CONSTITUTION:The crystalline silicon thin film is formed on a heated substrate by forming plasma of hydrogen and the reaction gas containing silicon by the use of high frequency excited plasma so that a silicon film is deposited by chemical gas phase growing method. The reaction pressure is 0.5-10Torr and the proportion of hydrogen gas as the diluent gas is specified to 50-150 times as that of the reaction gas containing silicon atoms. The heating temp. of the substrate is 400-600 deg.C and the power density of the high frequency excited plasma is 0.05-1.0W/cm<2>. Thereby, a good crystalline silicon thin film can be obtained at a low cost.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of manufacturing a crystalline silicon film on a substrate such as a glass substrate or a silicon substrate by chemical vapor deposition using plasma. For example, it is ideal for producing polycrystalline silicon on a large area at low temperature on a glass substrate used in LCD televisions, projection televisions, printers, image scanners, etc. using polysilicon thin film transistors, and providing cheaper polysilicon films. Regarding the manufacturing method.

[Prior Art] Conventionally, crystalline silicon has an electron field effect mobility that is several tens of times higher than that of amorphous silicon. For example, if a thin film transistor is made of this crystalline silicon, it can be used as a switching element with a fast response speed. . However, the conventionally proposed chemical vapor deposition methods for producing crystalline silicon films include atmospheric pressure chemical vapor deposition (hereinafter referred to as normal pressure CVD), low pressure chemical vapor deposition (hereinafter referred to as low pressure CVD), C
VD method), plasma chemical vapor deposition method C (hereinafter simply referred to as plasma CVD method), etc. These methods are used to form a crystalline silicon thin film on a glass substrate using, for example, reduced pressure C.
A method is used in which the VD method is used and the substrate temperature is set at about 500 to 700°C.

However, the production temperature is high, making it difficult to uniformly form a film over a large area on a glass substrate or the like. Therefore, the crystallinity of silicon thin films formed by low pressure CVD or plasma CVD is improved by using solid phase growth or by laser annealing.

However, solid-phase growth requires baking at a high temperature of 500 to 700°C for a long time of 10 to 20 hours, and laser annealing also requires a long processing time, which reduces factory productivity and costs. There are many problems in terms of.

[Problems to be Solved by the Invention] In view of the above-mentioned prior art, the present invention is a manufacturing process that allows the formation of a crystalline silicon film on an arbitrary substrate at a relatively low substrate heating temperature and thus over a large area. It is intended to provide a method.

[Means for Solving the Problems] The present invention provides a method for producing a crystalline silicon film on a heated substrate by chemical vapor deposition by converting a reaction gas containing silicon atoms and hydrogen gas into plasma using radio-frequency excited plasma. , a method for producing a thin crystalline silicon film, characterized in that the reaction pressure is 0.5 to 10 Torr and the ratio of hydrogen gas, which is a diluent gas, to the reaction gas containing silicon atoms is 50 to 150 times.

Examples of reactive gases containing silicon atoms include hydrides such as silane (SiH4) and disilane (S1zHi), and silane tetrafluoride (SiFa) and silane tetrachloride (SiC).
Halides such as Ii), or S+Ho~4X4~
. There is a halogen hydride of silane represented by (X: halogen atom).

In addition, the reaction pressure is 0.5 in a reactor using plasma.
Below Torr, it becomes relatively difficult to produce a thin film uniformly over a large area, and when above 10 Torr, it becomes difficult to generate plasma unless the high frequency power density is increased.

The ratio of hydrogen gas, which is a diluent gas, is such that the reaction pressure is 2 To
rr, the high frequency power density is 0.8 W/cm", and the substrate temperature is 400°C, 5iH-/Hz = 1/4
The results of X-ray diffraction analysis of silicon films prepared in the range of 0 to 1/100 are shown in FIG.

According to Figure 2, crystallization begins at 1150 or higher, and 1/
The crystallinity gradually improves up to 100. It can be said that the dilution ratio in the practical range is 50 to 150 times.

The high frequency power density greatly affects the crystallinity of the silicon film. That is, in the method for manufacturing a crystalline silicon film of the present invention, when S i Ha/Ht = 1/80, reaction pressure is 2 tons orr, and substrate temperature is 450°C, the high frequency power density is 0.05 to 2.0 W/. The silicon film was crystallized in the range of 0.05 to 1.cm'', and an amorphous silicon film was deposited under other conditions.
The grain size increased in the range of m''.

Regarding the effect of the substrate temperature, the silicon film is crystallized even at 250° C. under the manufacturing conditions of the present invention, but the crystal grain size is small and the crystallinity of the entire film is also low. Increase the substrate temperature to 400'
When the temperature is higher than C, the entire film is crystallized when the crystal grain size is 500 Å or more. Using a plasma CVD device, S i H4/
Hz = 1/64, high frequency power density 0.08W
Figure 1 shows the relationship between the substrate temperature and the crystallinity determined by X-ray diffraction of a silicon film deposited at /cm2 and a pressure of 2 Torr. According to the figure, as the temperature rises, the crystallinity also improves. This is thought to be due to the substrate temperature increasing the diffusion energy of atoms on the substrate surface during the rearrangement of atoms during crystal growth of the silicon film, helping them to bond to stable sites.

[Operation] Although the mechanism of the present invention is not clear, when a silicon film is deposited on a substrate, hydrogen radicals participate in a surface reaction between dangling bonds of silicon on the substrate surface and Si radicals involved in the deposition. It is believed that a crystalline silicon film is deposited only in the presence of a moderate amount of hydrogen radicals. According to the present invention, it is possible to omit conventional complicated and time-consuming processes such as solid phase growth and laser annealing, and it is possible to provide an inexpensive and good crystalline silicon thin film.

[Example 1] Hereinafter, the present invention will be explained in detail based on Examples, but the present invention is not limited thereto.

(Example 1) A low expansion glass such as Corning 7059 manufactured by Corning Co., Ltd. or NA-20 manufactured by Asahi Glass Co., Ltd. was used as a substrate. After cleaning the substrate, raw material gases were converted to Si H4 and H2 using a glow discharge plasma CVD apparatus. , power density Q, lW/cm
” with a dilution rate of Hz/S r H4-60/1,
When a silicon thin film was deposited at a pressure of 2 Torr and a substrate temperature of 400°C, a polycrystalline silicon thin film with a grain size of about 500 grains could be obtained.

The field effect mobility of the thin film transistor formed using the crystalline silicon film produced in this way is 50 cm2/ν
・Showed good characteristics of S or higher.

(Example 2) Also, as in Example 1, a glow discharge plasma CVD device was applied to a glass substrate! using SiH4 and H2 as raw materials,
When silicon '111M was deposited at a dilution rate of HZ/S + H4 = 80/1 at a power density of 0.5 W/cm'', a pressure of I Torr, and a substrate temperature of 500'C, the grain size was 1000 nm polycrystalline silicon. A thin film was obtained.Furthermore, the field effect mobility of the thin film transistor formed in the same manner as in Example 1 was 100 cm2/V-S or more, showing good characteristics.

(Example 3) Glow discharge plasma CV was applied to a glass substrate in the same manner as in Example 1.
Using apparatus D, a silicon thin film was prepared using source gases of 5iz H6 and H2, a dilution rate of H,/S i , H, = 60/1, a power density of 0.5 W/cm'', a pressure of 5 Torr, and a substrate temperature of 550°C. When deposited, a polycrystalline silicon thin film with a grain size of 1000 nm could be obtained.

Further, the field effect mobility of the thin film transistor formed in the same manner as in Example 1 was 100 cm''/V -S or more, which showed good characteristics.

[Effects of the Invention] As described above, in the present invention, a reaction gas containing silicon atoms and hydrogen are turned into plasma using high-frequency excited plasma, and the reaction pressure is 0.5 to 1OT.

When plasma chemical vapor deposition is performed at rr with a ratio of reactant gas containing silicon atoms to hydrogen in the diluent gas of 1150 to 1/150, a crystalline silicon thin film with large grain size can be formed relatively easily on a glass substrate at low temperature. It is possible. By using a crystalline silicon thin film with a large grain size, it is possible to form a crystalline silicon thin film transistor with good transistor characteristics, and it is also possible to form a thin film over a large area. - Fabrication of matrix-type LCDs becomes economical, improving factory productivity and reducing product costs.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an X-ray diffraction analysis of a crystalline silicon film deposited by changing the temperature of a glass substrate according to the manufacturing method of the present invention. FIG. 2 is a graph showing X-ray diffraction analysis of crystalline silicon films deposited on a glass substrate by the manufacturing method of the present invention with varying ratios of reactive gas (SiH, ) and hydrogen (H2). Patent application: Toppan Printing 1 Co., Ltd. Representative: Kazuo Suzuki

Claims (4)

[Claims] (1) A method for manufacturing a crystalline silicon film in which a reactive gas containing silicon atoms and hydrogen gas are turned into plasma using radio-frequency excited plasma, and a silicon film is deposited on a heated substrate by chemical vapor deposition, in which the reaction pressure is 0. .5-1
A method for manufacturing a crystalline silicon film, characterized in that the ratio of hydrogen gas, which is a diluent gas, to a reaction gas containing silicon atoms is 50 to 150 times at 0 Torr. (2) The method for manufacturing a crystalline silicon film according to claim (1), wherein the heating temperature of the substrate is 400 to 600°C. (3) The high frequency power density of the high frequency excited plasma is 0.
2. The method for producing a crystalline silicon film according to claim 1, wherein the electric power is 0.05 to 1.0 W/cm^2. (4) The method for producing a crystalline silicon film according to claim 1, wherein the reactive gas containing silicon atoms is SiH_4 or Si_2H_6.