JPH04235282A - Optical cvd method and optical cvd apparatus - Google Patents

Abstract

PURPOSE:To form thin film having excellent characteristic on a substrate to be coated by mixing hydrogen radical generated by thermal decomposition reaction of a metal with raw material gas and utilizing photochemical reaction. CONSTITUTION:SiH4 as the raw material gas is introduced into a vessel 11 charging Hg 10 and introduced into a reaction chamber 18 as the mixed gas with Hg vapor and also H2 gas is introduced into a catalyst flange 22 and the hydrogen radical is generated by thermal catalytic reaction by using W-made heater 21 and introduced into the reaction chamber 18 and mixed. Optical energy from a low pressure mercury lamp 13 irradiates this mixed gas through a qualtz glass window 14 to decompose SiH4 gas, and amorphous hydrogenized Si film having excellent characteristic is formed on the substrate 5 heated with a heater 17.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

[Industrial Application Field] The present invention relates to optical C
It relates to the VD method and optical CVD equipment.

0002

[Prior Art] In recent years, photoCVD has been used as a method for forming functional thin films made of hydrogenated amorphous silicon, etc.
Method D is attracting attention. This is a method in which a source gas such as silane gas is decomposed using a photochemical reaction to form a thin film on a substrate. Compared to the thermal CVD method, this method has
Since thin films can be formed at low temperatures, there are fewer defects caused by thermal desorption of hydrogen, and plasma CV
Compared to the D method, film formation is performed only by radical reactions, so there is no charged particle damage to the substrate to be processed.
A good thin film can be formed.

FIG. 3 is a cross-sectional view showing an outline of an example of a conventional device using the photo-CVD method. In the figure, 31 is a mercury reservoir;
32 is a gas inlet, 33 is a light source, 34 is a window glass, 35
3 is a substrate to be processed; 36 is a substrate holder; 37 is a heater;
8 is a reaction chamber, and 39 is a gas exhaust port. In this apparatus, the raw material gas passes through the mercury reservoir 31, and at this time becomes a mixed gas with mercury 310 vapor and is introduced into the reaction chamber 38. Light from the light source 33 enters the reaction chamber 38 through the window glass 34, and the mixed gas is reacted and decomposed by the light energy, thereby placing the substrate on the substrate holder 36 heated by the heater 37. A thin film is formed on the substrate 35 to be processed.

However, in such a photo-CVD apparatus, for example, in a hydrogenated amorphous silicon thin film,
Jpn. J. Appl. Phys. 27 (1987
) As shown in L1573, the silicon defect density in a thin film measured by electron spin resonance method is
15/cm3 or less. Therefore, carrier mobility, which depends on the defect density, cannot be increased, which has been an obstacle to improving the responsiveness of transistors and the like using this thin film.

[0005]

As described above, the conventional photo-CVD apparatus has a problem in that the formed thin film has a high defect density and thus has a low carrier mobility.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a photo-CVD method and a photo-CVD apparatus that can form a thin film with good characteristics. . [Structure of the invention]

[0007]

[Means for Solving the Problems] The gist of the present invention is to generate hydrogen radicals through a thermal decomposition reaction of a metal, mix the hydrogen radicals with a raw material gas, and apply a photochemical reaction to a thin film on a substrate to be processed. The goal is to form a

[0008]

[Operation] According to the present invention, hydrogen radicals are generated and used in forming a thin film, thereby making it possible to form a good thin film with few defects.

[0009] Since the thermal decomposition reaction of metal is used as a method for generating hydrogen radicals, high-energy particles such as hydrogen ions are not generated. Therefore, thin film formation can be performed without plasma damage.

[0010] Furthermore, these hydrogen radicals can, for example, cover a hydrogenated amorphous silicon thin film with a raw material gas, silane (Si).
When generated from H4), a reaction of SiH4 + H (hydrogen radical) → SiH3 (radical) + H2 occurs to form SiH3 radicals, which are considered optimal for forming a silicon network with few defects. By the hydrogen radicals generated by the present invention, SiH3
Radicals can be obtained more abundantly than before, and a better thin film can be formed.

Furthermore, these hydrogen radicals can be used to remove excess hydrogen from the thin film surface without damaging the thin film, or to remove excess hydrogen from the thin film surface without damaging the thin film. It has the effect of removing bonds. According to the present invention, more hydrogen radicals reach the thin film surface than before, so a better thin film can be formed.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below with reference to illustrated embodiments.

FIG. 1 is a diagram showing a schematic structure of a photo-CVD apparatus according to an embodiment of the present invention. In the figure, 11 is a mercury reservoir, 1
2 is a mixed gas inlet, 13 is a low-pressure mercury lamp, 14 is synthetic quartz glass, 15 is a substrate to be processed, 16 is a substrate holder, 17 is a heater, 18 is a reaction chamber, and 19 is a gas exhaust port. It shows. Further, 20 indicates an inlet for gas containing hydrogen radicals, 21 indicates a tungsten heater, and 22 indicates a catalyst flange.

In this apparatus, the silane used as the raw material gas passes through the mercury reservoir 11 heated to 80 degrees.
At this time, it becomes a mixed gas with mercury vapor and is introduced into the reaction chamber 18. Hydrogen gas is introduced into the catalyst flange 22 and causes a thermal catalytic reaction with the heated tungsten heater 21. This reaction decomposes hydrogen molecules and generates hydrogen radicals. Thereafter, this gas containing hydrogen radicals is introduced into the reaction chamber 18. The mixed gas and the gas containing hydrogen radicals are mixed in the reaction chamber 18. This reaction chamber 1
8 is a low pressure mercury lamp 13 passed through a synthetic quartz glass 14.
The light from
Warmed to 0 degrees. Due to the energy, reaction chamber 1
A hydrogenated amorphous silicon film was formed on the substrate 15 to be processed by reacting and decomposing the gas mixed in the chamber 8 .

FIG. 2 shows the silicon defect density of hydrogenated amorphous silicon films prepared by varying the current value of the tungsten heater according to the present invention. Silicon defect density was measured by electron spin resonance method. By increasing the current value of the tungsten heater, the silicon defect density decreases,
2 x 1014cm- with tungsten heater current 6A or more
A hydrogenated amorphous silicon film of No. 3 was obtained. Here, the tungsten current is 3 A or more, that is, hydrogen radical generation amount (mol)/SiH4 gas supply amount (mol)
)>0.1, a good hydrogenated amorphous silicon film with a silicon defect density of 1015 cm-3 or less can be produced.

It should be noted that the present invention is not limited to the embodiments described above. For example, although silane was used as the raw material gas, other gases such as disilane may be used. Moreover, although hydrogen radicals were generated in the flange and introduced into the reaction chamber, it is sufficient if the hydrogen radicals can be introduced near the surface of the substrate to be processed. Also,
Although a thermal catalytic reaction was used as a method for obtaining hydrogen radicals, any reaction that does not produce ions, such as a photolysis reaction, may be used. Furthermore, the metal used in the thermal catalytic reaction was tungsten, but Ta, Mo, Ti, Zr, Fe, Ca, Ba, N
Any metal with a high melting point that can serve as a hydrogenation catalyst may be used, such as Pt, Rh, Pd, etc. In addition, various modifications can be made without departing from the gist of the present invention.

[0017]

[Effects of the Invention] As detailed above, according to the present invention,
It becomes possible to form a thin film with low defect density and good characteristics.

[Brief explanation of the drawing]

[Fig. 1] A cross-sectional view showing a schematic structure of a photo-CVD apparatus according to an embodiment of the present invention.

[Fig. 2] A diagram showing the relationship between the defect density of a hydrogenated amorphous silicon film produced in an example of the present invention and the current passed through a tungsten heater.

[Figure 3] Cross-sectional view showing the schematic structure of a conventional optical CVD device

[Explanation of symbols]

10, 30...Mercury 11, 31...Mercury reservoir 12, 32...Mixed gas inlet 13...Low pressure mercury lamp 14...Synthetic quartz glass 15, 35...Substrate to be processed 16, 36...Substrate holder 17, 37...Heater 18, 38 ...Reaction chambers 19, 39 ...Gas exhaust port 20 ...Inlet port 21 for gas containing hydrogen radicals
...Tungsten heater 22 ...Catalyst flange 33 ...Light source 34 ...Window glass

Claims (6)

[Claims] 1. When forming a thin film on a substrate to be processed by a photochemical reaction, a gas containing hydrogen radicals obtained by decomposing hydrogen molecules is introduced into a reaction chamber in which the substrate to be processed is installed. Features of optical CVD method. 2. The photo-CVD method according to claim 1, wherein the gas containing the hydrogen radicals is introduced into the reaction chamber near the surface of the substrate to be processed. 3. The photo-CVD method according to claim 1, wherein a mercury sensitization reaction is utilized during thin film formation. 4. The photo-CVD method according to claim 1, wherein at least one of a thermal catalytic reaction and a photodecomposition reaction of a metal is utilized when hydrogen radicals are generated. 5. The metal used in the thermal catalytic reaction contains W. T
a. Mo. Ti, Zr, Fe, Ca, Ba, Ni, Pt
5. The photoCVD method according to claim 4, wherein at least one of , Rh, and Pd is used. 6. A reaction chamber in which a substrate to be processed is installed and into which a raw material gas for film formation is introduced, a light source for irradiating light onto the substrate to be processed in the reaction chamber, and a light source in the reaction chamber. A photo-CVD apparatus comprising means for generating a gas containing hydrogen radicals to be introduced.