JPH04144122A - Manufacture of polycrystalline silicon thin film - Google Patents

Abstract

PURPOSE:To obtain a polycrystalline silicon film which has a high crystallinity and is most suitable to an active device such as a thin film transistor by a method wherein, when the polycrystalline silicon film is formed by a solid phase growth method in which an amorphous silicon film is heated, the refractive index and the attenuation factor of the amorphous silicon film are selected to be within respective specific ranges corresponding to different wavelengths. CONSTITUTION:An amorphous silicon film is heated to form a polycrystalline silicon film by a solid growth method. At that time, the refractive index (n) and the attenuation factor (k) of the amorphous silicon film are so selected as to be within respective specific ranges corresponding to different wavelengths. Those are: 250nm: n=1.88+ or -0.01, k=3.41+ or -0.01. 300nm: n=3.18+ or -0.01, k=3.70+ or -0.01. 350nm: n=4.44+ or -0.01, k=3.16+ or -0.01. 400nm: n=5.00+ or -0.01. k=2.22+ or -0.01. 450nm: n=5.07+ or -0.01, k=1.47+ or -0.01. 550nm: n=4.80+ or -0.01, k=0.63+ or -0.01. 600nm: n=4.65+ or -0.01, k=0.38+ or -0.01. 650nm: n=4.52+ or -0.01, k=0.17+ or -0.01. 700nm: n=4.65+ or -0.01, k=0.03+ or -0.01 750nm: n=4.35+ or -0.01, k=0.01+ or -0.01. 800nm: n=4.30+ or -0.01, k=0.01+ or -0.01. 850nm: n=4.25+ or -0.01, k=0.01+ or -0.01.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a polycrystalline silicon thin film, and particularly to a method for manufacturing a polycrystalline silicon thin film using a solid phase growth method.

(Prior art) In recent years, active devices such as polycrystalline silicon thin film transistors using polycrystalline silicon thin films have significantly improved operating speeds compared to active devices such as thin film transistors using amorphous silicon films. It is attracting attention and is expected to be applied particularly to contact sensors and drive circuits of liquid crystal display devices.

The operating speed of an active element used in such a contact sensor or a drive circuit section of a liquid crystal display device is required to be at least 8 MHz to 10 MHz or higher.

In order to meet such demands, a high electron mobility is required, and therefore a crystal grain size of at least 50 cj/■·S or more is required.

By the way, methods for manufacturing polycrystalline silicon thin films are being researched in various fields, and are broadly classified into liquid phase growth methods and solid phase growth methods.

Liquid phase growth methods include, for example, electron beam evaporation, physical thin film deposition such as sputtering, or reduced pressure C, V, D.

(Che+*1cal Vapor Deposit)
, Braz 7C,V.

After polycrystalline silicon or amorphous silicon obtained by chemical thin film deposition such as D, etc. is irradiated with a laser beam or an electron beam to a temperature higher than the melting point temperature to melt it,
It is recrystallized by cooling.

The solid-phase growth method uses polycrystalline silicon obtained by physical thin film deposition or chemical thin film deposition as described above, or amorphous silicon in which ions are further implanted into amorphous silicon, at a melting point of 550 to 650 ''C. By maintaining the temperature below for several hours, a polycrystalline silicon film with a large crystal grain size can be obtained.

(Problem to be Solved by the Invention) By the way, in the liquid phase growth method described above, a polycrystalline silicon film with good crystallinity can be obtained because polycrystalline silicon or amorphous silicon is melted and then recrystallized. Since it is in a highly molten state, more impurities are incorporated. Therefore, since the polycrystalline silicon film has low purity, there is a drawback that when applied to an active element such as a thin film transistor, highly reliable operation cannot be obtained.

On the other hand, solid-phase growth can produce good polycrystalline silicon films because there are no impurities mixed into the film during manufacturing, but it does not produce films with better crystallinity than liquid-phase growth. It has the disadvantage that it cannot be used.

The present invention has been made in view of the above-mentioned problems, and provides a method for manufacturing a polycrystalline silicon film using a novel solid-phase growth method. The present invention provides a method for manufacturing a polycrystalline silicon film that is optimal for active elements such as thin film transistors.

[Structure of the Invention] (Means for Solving the Problem) The method for manufacturing a polycrystalline silicon thin film of the present invention is a polycrystalline silicon film manufacturing method for manufacturing a polycrystalline silicon film by heating an amorphous silicon film to cause solid phase growth. A method for manufacturing a thin film, the refractive index (n) of an amorphous silicon film, an quencher fi (k
) is rrl, 88±0.0 at a wavelength of 250 nm
1. k=3.41±0.01. At wavelength 300r+a+, n=3.18±0.01. k=3.70±0
．． 01. At wavelength 350nrA, n=4.44±0
．． 01. k=3.16±0.01. Wavelength 400nIl
In, n-5,00±0.01. k-2,22±
0.01゜Wavelength 450ni l: Good, rr5.07
+0.01. k-1,47±0.01. wavelength 550
It is good for na, n-4,80±0.01. k-0,6
3±0.01. At wavelength B00na+, n-4, [
i5±0.01゜k-OJB±0.01. Wavelength B50n
m, n-4,52±0.01. k-0,17
±0.01. At a wavelength of 700 nm, n-4,43+
O, Ol, k-0,03±0.01. Wavelength 750nI
ll: Oite, tr4J5fO, OL, k-0, OL
±0.01. Wavelength 800nm l: set, rr4.3
0±0.01. k-0,01±0.01. wavelength 850
It is good for ni, n-4, 25±0.01. k-0,O
L+0.01. It is characterized by having certain characteristics.

(Function) The present inventors investigated the relationship between amorphous silicon, which is the starting material in the solid phase growth method, and polycrystalline silicon thin films manufactured using the same from various perspectives, and found the following. The facts have become clear.

That is, the smaller the voids in the amorphous silicon film that is the starting material, that is, the higher the density, the larger the grain size of each crystal in the polycrystalline silicon thin film that is finally produced.

The distance between the nearest neighboring atoms of amorphous silicon, which is used as a starting material and has a high density, is narrower than that of amorphous silicon, which has a low density. Therefore, the bonding energy between atoms in amorphous silicon, which has a highly dense film, is high, and the bonds between atoms are difficult to break.

For this reason, in amorphous silicon, which has a highly dense film, self-diffusion occurs during solid phase growth, and the frequency of crystal nucleus generation is lower than in amorphous silicon, which has a less dense film. becomes.

Therefore, if amorphous silicon, which has a highly dense film, is used as a starting material, the frequency of crystal nuclei generation is low, and the generated crystal nuclei can achieve sufficient crystal growth without interfering with the growth of adjacent crystal nuclei. becomes possible.

In addition, when amorphous silicon with high film density is used as a starting material, many silicon atoms exist within a short distance from the crystal nucleus, so once a crystal nucleus is generated, crystal growth progresses rapidly. I will do it.

For this reason, the higher the density of the amorphous silicon film that is the starting material, the larger the grain size of each crystal in the polycrystalline silicon thin film that is finally produced.
Furthermore, the time required for solid phase growth does not change significantly compared to the conventional method.

Furthermore, the present inventors have discovered that the density of the amorphous silicon film that is the starting material is clearly indicated by the refractive index (n) and extinction coefficient (k) determined by a spectroscopic ellipsometer.

Furthermore, various experiments were conducted, and it was found that the refractive index (n) and extinction coefficient (k) for each wavelength of amorphous silicon, which is the starting material, are within a predetermined range. We have discovered that this is an essential condition for obtaining crystalline silicon thin films.

The density of an amorphous silicon film is thought to be determined by the amount of voids in the amorphous silicon film, and the amount of voids in this film is determined by the refractive index (n) and extinction coefficient determined by a spectroscopic ellipsometer. This is thought to be because it greatly affects (k).

Note that the refractive index (n) and extinction coefficient (k) in this specification are determined using an automatic spectroscopic ellipsometer (SOPI?A'l+MM).
ulti-Optical-3pectrometry
c-3canner Model ES-4G).

If the refractive index (n) is smaller than the above range with respect to the wavelength, it means that the amount of voids in the film is large, making it impossible to obtain a polycrystalline silicon thin film with good crystallinity. . Conversely, if the refractive index (n) is larger than the above range, a polycrystalline silicon thin film with good crystallinity can be obtained, but it becomes difficult to form such a starting material, amorphous silicon. It is.

Similarly, regarding the extinction coefficient (k), if it is smaller than the above range, a polycrystalline silicon thin film with good crystallinity cannot be obtained, and conversely, an amorphous silicon film larger than the above range may be formed. This is because it is technically difficult.

In the present invention, as described above, the refractive index (n) for each wavelength is
By solid-phase growth using a dense amorphous silicon film with a predetermined extinction coefficient (k) as a starting material,
A polycrystalline silicon thin film with good crystallinity can be obtained even if it is produced in the same manner as before.

Furthermore, the above-mentioned dense amorphous silicon can be obtained by appropriately changing the conditions of conventionally known methods, particularly by using reduced pressure C or V using silane gas or disilane gas.

D9, plasma C, V, D, etc. by chemical thin film deposition, or silicon ions in polycrystalline silicon,
A method of implanting ions such as silicon hydride ions or silicon fluoride ions to make the material amorphous may be used.

(Example) Hereinafter, a method for manufacturing a polycrystalline silicon thin film according to an example of the present invention will be described in detail. (Specific example) Using a device with reduced pressures of C, V, and D, using disilane as a reaction gas, film formation temperature of 470 ''C, and gas pressure of OJtorr, refraction for each wavelength as shown in Table 1 was formed on an insulating substrate. An amorphous silicon film was deposited with a thickness of 0.2 microns, having a coefficient of extinction (n) and an extinction coefficient (k) of 0.02 microns.

Here, the refractive index (n) and extinction coefficient (
The measurement of k) was obtained using an automatic spectroscopic ellipsometer (manufactured by SOPRA).

When the distance between the nearest neighboring atoms of the amorphous silicon film is calculated from this density, it is 2.38 angstroms, which is very close to the distance between the nearest neighboring atoms of the single crystal silicon film, which is 2.35 angstroms.

Then, the substrate temperature was maintained at 600° C. for 24 hours, and solid phase growth was performed to obtain a polycrystalline silicon thin film. When the crystal grain size of the polycrystalline silicon thin film thus obtained was measured, it was found that a polycrystalline silicon thin film with good crystallinity was obtained with a crystal grain size of 2.0 to 3.0 microns.

(Comparative example) Using silane as a reaction gas using reduced pressure C, V, D, IM! An amorphous silicon film having a refractive index (n) and an extinction coefficient (k) for each wavelength as shown in Table 1 was deposited on an insulating substrate at a temperature of 50°C and a gas pressure of 0.4 torr. It was deposited to a film thickness of 2 μm.

Here, the refractive index (n) and extinction coefficient (
The measurement of k) was obtained using an automatic spectroscopic ellipsometer in the same manner as in the above-mentioned specific example.

The distance between the nearest adjacent atoms of the amorphous silicon film is calculated from this density to be 2443 angstroms, which is considerably larger than the specific example.

Then, as in the specific example, the substrate temperature was maintained at 800° C. for 24 hours, and solid phase growth was performed to obtain a polycrystalline silicon thin film. When the crystal grain size of the polycrystalline silicon thin film thus obtained was measured, it was found that a polycrystalline silicon thin film with a crystal grain size of 0.1 micron was obtained.

As is clear from the above-mentioned specific examples and comparative examples, the refractive index (n) and extinction coefficient (k) for each wavelength of amorphous silicon, which is the starting material for solid phase growth, are set within a predetermined range. As a result, a polycrystalline silicon thin film with good crystallinity can be easily produced.

In addition to the specific examples mentioned above, for example, reduced pressure C9V,
D. Another relatively easy method for realizing the present invention is to form an amorphous silicon film or a polycrystalline silicon thin film using an apparatus and then implant silicon ions into the film under predetermined conditions.

[Effects of the Invention] As detailed above, according to the method for producing a polycrystalline silicon thin film of the present invention, the drawback of the solid phase growth method, which is that it is difficult to obtain a polycrystalline silicon thin film with a large crystal grain size, can be overcome. We were able to solve this problem and obtain a polycrystalline silicon thin film as good as that obtained by liquid phase growth.

Furthermore, compared to the liquid phase growth method, there is no contamination of impurities into the film, and a highly pure polycrystalline silicon thin film can be obtained.

Agent: Patent Attorney Noriyuki Chika Same Bamboo Flower Kikuo

Claims (1)

[Scope of Claims] A method for manufacturing a polycrystalline silicon thin film in which a polycrystalline silicon film is manufactured by heating an amorphous silicon film to cause solid phase growth, the refractive index (n) and extinction of the amorphous silicon film comprising: Attenuation coefficient (k)
At a wavelength of 250 nm, n=1.88±0.01, k
= 3.41 ± 0.01, at wavelength 300 nm, n = 3.18 ± 0.01, k
=3.70±0.01, at wavelength 350nm, n=4.44±0.01, k
=3.16±0.01, n=5.00±0.01, k at wavelength 400nm
=2.22±0.01, at wavelength 450nm, n=5.07±0.01, k
= 1.47 ± 0.01, at wavelength 500 nm, n = 4.96 ± 0.01, k
=0.97±0.01, at wavelength 550nm, n=4.80±0.01, k
=0.63±0.01, at wavelength 600nm, n=4.65±0.01, k
=0.38±0.01, at wavelength 650nm, n=4.52±0.01, k
=0.17±0.01, at wavelength 700nm, n=4.43±0.01, k
=0.03±0.01, at wavelength 750nm, n=4.35±0.01, k
=0.01±0.01, at wavelength 800nm, n=4.30±0.01, k
=0.01±0.01, at wavelength 850nm, n=4.25±0.01, k
=0.01±0.01, A method for producing a polycrystalline silicon thin film.