JPH04318921A - Manufacture of polycrystalline silicon film - Google Patents

Abstract

PURPOSE:To grow a polycrystalline silicon film on a glass substrate at a low temperature of about 200 deg.C by diluting gas, which contains silicon, with hydrogen at large flow rate, and growing a film with a plasma CVD device. CONSTITUTION:In the case that silane is used for reaction gas, the flow ratio of hydrogen gas to silane gas; SiH4/H2 is 1.0-5.0%, and substrate temperature is 200-300 deg.C, and the distance W between electrodes is less than 45mm. A film is grown on a glass substrate 8, with high frequency power as 0.01-5.0W/cm<2>. Since poly-Si can be made at about 200 deg.C in substrate temperature, low-melting point glass can be used, and it has great effect on cost reduction of a TFT device. Moreover, since halogen etching gas is not used, there is no mixing in of impurities, which cause the deterioration of the property of a device, in the film. And the film is produced in hydrogen gas plasma, so hydrogen passiration is not necessary after the film formation. Thus high quality poly-Si thin film can be formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing polycrystalline silicon thin films that can be applied to semiconductor devices such as thin film transistors, and more particularly to a method for manufacturing polycrystalline silicon thin films that can be formed at low temperatures on substrates such as low-melting glass.

0002

2. Description of the Related Art Attempts are being made to create high-performance thin film transistors (TFTs) using microcrystalline or polycrystalline Si (poly-Si) as element materials on low-melting point glass substrates. In particular, a low melting point glass substrate such as Corning's 7059 substrate is used as the substrate, and the maximum temperature of the process is 450°C.
The practical application of a process for producing TFTs with high mobility and a high ON/OFF ratio at temperatures below about 0.degree. C. is eagerly awaited.

Conventionally, in order to form a poly-Si film on a glass substrate, a method is known in which monosilane gas is thermally decomposed at a substrate temperature of about 600° C. using a low-pressure CVD method. In addition, conventional methods for creating high-performance poly-Si TFTs include forming TFTs by forming poly-Si in which amorphous Si (a-Si) is made large in size by solid-phase growth; There is a method of melting and recrystallizing -Si or poly-Si by laser annealing to create a TFT.

0004

[Problem to be solved by the invention] Pol
In the method of forming a y-Si film, low melting point glass cannot be used for the substrate due to the film forming temperature requirements. In addition, in order to obtain large grain size poly-Si by solid phase growth method, 6
This requires annealing for a long time of 4 to 70 hours at a temperature of about 0.000C, and low melting point glass cannot be used for the substrate. Laser annealing has problems such as variations in device characteristics due to non-uniform characteristics of the laser beam and low throughput.

[0005] For this reason, Japanese Patent Application Laid-Open No. 63-175417, Japanese Patent Application Publication No. 2-177368, Japanese Patent Application Publication No. 2-202018, Ma
terials Research Society
Symposia Proceedings, Vo
lume95, p. 225 (1987), polycrystalline silicon is produced at low temperatures by glow discharge decomposition of a mixed gas of silane gas and etching gases such as fluorine and fluorosilane using plasma chemical vapor deposition (PCVD). Methods that can be used to do this are attracting attention.

Poly-S obtained by these film-forming methods
Since the i-thin film contains a halogen gas such as fluorine gas and a halide such as fluorosilane and dichlorosilane as an etching gas, the obtained poly-Si contains halogen atoms such as fluorine and chlorine as impurities. pol
When manufacturing a y-Si TFT, these impurities pose a major problem because they cause crystal defects and increase leakage current of the TFT.

The method for manufacturing a polycrystalline silicon thin film disclosed in Japanese Patent Application Laid-Open No. 2-248038 uses hydrogen as an etching gas, so there is no problem of impurity contamination as described above. However, since the activation state of hydrogen is controlled by providing an activation chamber separate from the reaction gas, there is a problem that the apparatus becomes complicated. In addition to the above-mentioned problems, the method for manufacturing semiconductor thin films described in Japanese Patent Publication No. 3-8102 has the disadvantage that the resulting thin film is a mixture of amorphous silicon and polycrystalline silicon, making it unsuitable for application to TFTs. There were also problems.

The present invention solves the above problems, and its purpose is to provide a method for forming a film of high quality poly-Si, which does not contain impurities such as halogen gas, using a simple device at a low temperature. It is in.

[0009]

[Means for Solving the Problems] The method for manufacturing a polycrystalline silicon thin film of the present invention is a method for forming polycrystalline silicon on a substrate by glow discharge decomposition of a silicon-containing gas by plasma excitation. It is characterized in that the activation state of hydrogen is controlled by adjusting the distance between the glow discharge electrodes.

0010

EXAMPLES The manufacturing method of the present invention will be described in detail below. The substrate used may be a substrate other than single crystal Si, such as a low melting point glass, a ceramic substrate, or a quartz substrate. If single crystal Si is used for the substrate, an epitaxial Si film can be obtained instead of poly-Si. In this example, a 7059 substrate manufactured by Corning was used. The PCVD apparatus used was a PED-302 model manufactured by ANELVA, which has parallel plate electrodes. FIG. 1 shows a schematic diagram of the PCVD apparatus used in the present invention. 1 is a reaction chamber, 2 is an exhaust pipe, 3 is a counter electrode, 4 is a gas blowing hole, 5 is a gas introduction part, 6 is a high frequency application electrode, 7 is a substrate heater, 8 is a substrate, and 9 is a high frequency power source. W in FIG. 1 represents the distance between electrodes. SiH4 is used as the film forming gas.
, Si2H6, Si3H8, etc., and a mixed gas of H2 are used. In this example, a mixed gas of silane (SiH4) and H2 was used.

The basic reaction mechanism follows Formula 1 shown below. In the reaction of Formula 1, R1 is a film forming reaction and R2 is an etching reaction.

0012

[Formula 1] (n is a dimensionless number) In formula 1, as the hydrogen concentration increases, the reaction of R2 becomes dominant, so the Si-H bond with weak bond energy is selectively broken by the etching reaction of R2. . Therefore, only Si-Si bonds remain, and under these conditions, poly-Si bonds remain on the substrate.
is deposited. On the other hand, when the silane gas concentration increases, the film formation reaction of R1 in Equation 1 becomes dominant, and amorphous silicon (a-Si) with a high hydrogen concentration is formed on the substrate. Such a competitive relationship between R1 and R2 can be easily adjusted by changing the ratio of the silane gas concentration to the hydrogen gas concentration.

[0013] Therefore, in order to form a poly-Si thin film, it is necessary to dilute the silane gas with a large flow of hydrogen gas and to make the silane concentration/hydrogen concentration ratio at least 0.1 or less. When actually forming a poly-Si film, the silane/hydrogen gas concentration ratio is the gas flow rate ratio: SiH4/H2=0.
5 to 5.0%, particularly 1.0 to 3.0% is desirable. 0.
If it is less than 5%, the etching reaction by hydrogen gas becomes too dominant, the deposit rate becomes extremely small, and only poly-Si with a small particle size is formed. When it exceeds 5.0%, the film forming reaction becomes dominant and only a-Si is formed.

[0014] The pressure inside the reaction chamber is 0.1 to 10.0 Torr.
r is particularly preferably 0.3 to 1.5 Torr. The high frequency power for generating plasma has a power density of 0.01 to 5.
0W/cm2, preferably 0.03-0.06W/cm
Set it to 2. If it is less than 0.01 W/cm2, the etching reaction becomes too weak, and if it exceeds 5 W/cm2, the thin film will suffer plasma damage, making it impossible to form a high quality film. The substrate temperature is 100-600°C. Preferably 200℃~400℃
℃. When the substrate temperature is lower than 100° C., a-Si is deposited, and when the substrate temperature is higher than 600° C., the advantages of low-temperature film formation PCVD cannot be utilized.

An important condition for forming a poly-Si film is the distance between opposing electrodes (hereinafter referred to as interelectrode distance; W in FIG. 1) of the parallel plate type PCVD apparatus. In order for the etching reaction to proceed, the distance between the electrodes must be sufficiently short and hydrogen must reach the substrate in an active state. When the distance between the electrodes is long, the etching reaction occurs in the gas phase, and amorphous silicon is deposited on the substrate. Therefore, the inter-electrode distance W is defined by high frequency power and pressure. High frequency power is 0.
When the pressure is 03 W/cm2 and 1.2 Torr, the distance W between the electrodes is less than 45 mm, preferably 27 mm or less,
More preferably, it needs to be 20 mm or less. Before film formation, S
iH4:H2 = 1.8:98.2 mixed gas at a total flow rate of 2
The internal pressure was adjusted to the pressure shown in Table 1. After setting the substrate temperature to the temperature shown in Table 1, the film forming gas was flowed for about 20 minutes until the substrate temperature stabilized. Next, using a 13.56 MHz high frequency power source, the discharge power was 0.
A silicon thin film was grown on the glass substrate by discharging at 0.3 W/cm2 for 120 minutes. The growth rate was 9-22 Å/min. The average particle size of the obtained poly-Si was measured by X-ray diffraction.

Table 1 shows various properties of poly-Si produced by the production method of the present invention. As is clear from Table 1, even with a relatively thin film thickness of 1000 Å, a poly-Si film having a crystal grain size of about 1000 Å is formed. In addition, the crystal orientations of all the films shown in Table 1 are (111) and (
220) azimuthal X-ray diffraction peaks have been observed, especially N
o. 3.No. In the film of No. 4, a poly-Si thin film with preferential orientation in the (220) direction was obtained. When using a halogen gas as the etching gas, the film thickness is 2500 mm.
It is known that polycrystalization begins at a temperature of 1.5 Å or more, making it difficult to make a thin film. However, according to the manufacturing method of the present invention,
Since it is also possible to make the y-Si film thinner, it has a great effect when applied to TFTs.

[0017]

[Table 1]

Table 2 shows a comparative example in which the distance between the electrodes is 45 m.
Table 1 shows various properties of the Si thin film formed in the same manner as in Table 1, where m is the same. As is clear from Table 2, poly-Si was not obtained under the conditions shown in the comparative example, but a-Si was formed.

[0019]

[Table 2]

In the present invention, a p-type or n-type poly-Si film can be formed by mixing a doping gas of Group III or V of the periodic table of elements into the film-forming gas. Examples of the doping gas include diborane, phosphine, arsine, and the like.

[0021]

As described above, according to the present invention, a high quality poly-Si film can be formed at a low temperature of about 200°C. Therefore, a glass substrate with a low melting point can be used as the substrate glass, and the temperature of the TFT manufacturing process can be lowered. Therefore, if the present invention is used, a low-cost glass substrate can be used, which has a great effect on reducing the cost of devices such as liquid crystal displays, contact image sensors, and solar cells. Furthermore, the necessary equipment is a normal plasma CVD equipment, and no additional equipment for activating hydrogen gas is required.

Furthermore, since the present invention does not use any halogen-based gas, it has the great advantage that impurity elements such as fluorine that adversely affect the characteristics of TFTs are not mixed into the poly-Si film.

[0023] Furthermore, poly-Si thin films obtained by LPCVD, solid-phase growth, laser annealing, etc. have a problem in that their electrical properties deteriorate due to dangling bonds at their grain boundaries. In order to solve this problem, it was necessary to passivate the dangling bonds by means such as hydrogen plasma after forming a poly-Si film. However, the method of the present invention has the advantage that since the poly-Si film is exposed to hydrogen plasma during film formation, there is no need to perform hydrogen passivation afterwards.

Furthermore, the poly-Si thin film obtained by the LPCVD method, solid phase growth method, laser annealing method, etc.
111}, whereas the poly-Si thin film obtained by the method of the present invention has a {110} preferential orientation. It is known that the electron mobility in the in-plane direction (horizontal direction) of a poly-Si thin film is larger in {110}-coordinated poly-Si than in {111}-coordinated poly-Si. Therefore, the use of poly-Si obtained by the method of the present invention also has the great advantage that high performance TFTs with high electron mobility can be easily produced. The present invention also provides TFTs for load elements of highly integrated SRAMs of 4M bits or more.
The present invention is also highly effective when applied to general semiconductor devices such as ICs, LSIs, and three-dimensional SOI devices.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the PCVD apparatus used in the present invention.

[Explanation of symbols]

1……Reaction chamber 2...Exhaust pipe 3……Counter electrode 4...Gas blowout hole 5...Gas introduction part 6...High frequency application electrode 7...Substrate heater 8......Substrate 9……High frequency power supply

Claims (1)

[Claims] Claim 1: In a method of decomposing silicon-containing gas by glow discharge by plasma excitation to form polycrystalline silicon on a substrate, the activation state of hydrogen on the substrate is adjusted by adjusting the distance between the glow discharge electrodes. 1. A method for producing a polycrystalline silicon thin film, the method comprising: controlling the production of a polycrystalline silicon thin film;