JPS60241214A - Forming method of amorphous silicon film - Google Patents

Abstract

PURPOSE:To form an a-Si film of high quality on a substrate at a speed of the same degree as a conventional vacuum deposition by employing as a raw material such as a deposition source or a target solid silicon which contains hydrogenated silicon. CONSTITUTION:In a vacuum deposition method, a substrate 12 to be heated by a heater 11 is placed in a vessel 10 to be evacuated in vacuum by a vacuum pump 6, and a solid hydrogenated silicon 14 is placed in a vessel 13 to oppose to the substrate. The silicon 14 is evaporated by an electron beam supplied from an electron gun 15 to form an a-Si film on the substrate 12. In order to increase the uniformity of the formed film, the substrate is rotated. Thus, the a-Si film of high quality can be formed on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an amorphous silicon film.

Amorphous silicon films obtained on substrates using simple silicon by vacuum evaporation or sputtering have many localized units, making it impossible to control the conductivity type such as p-type or n-type, making it difficult to control functional devices. It has not attracted attention as a semiconductor material for obtaining. On the other hand, monosilane gas (5
It has been discovered that conductivity type can be controlled in an amorphous silicon film formed on a substrate by glow discharge decomposition (plasma CVD) using IH4). As is well known, silicon (abbreviated as A-81) has been actively researched and developed and is now becoming an important material for various devices such as solar cells.

It is said that the reason why the conductivity type can be controlled in this a-81 film is as follows. In other words, a considerable amount of hydrogen is incorporated into the Todoroki-81 film formed by glow discharge decomposition of monosilane gas, and these hydrogens combine with dangling bonds in the silicon to form a bond within the film. The localized level is reduced, and as a result, the conductivity type can be controlled. This is a useful method for controlling the conductivity type of amorphous silicon films.
It has been found that in order to obtain a -81 film, it is essential that a portion of the film be hydrogenated.

This means that a- containing hydrogen (partially hydrogenated)
As long as the 81 film can be obtained, any method other than the above-mentioned 5tH4 gas glow discharge decomposition (plasma CVD) method may be used, and in fact, various methods have been considered and are being put into practical use. These a-8t film forming methods will be briefly explained below.

The glow discharge decomposition method (plasma CVD method) described above involves introducing 5i) I4 gas into a vacuum container in which a substrate is placed, and applying direct current or alternating current power to the electrodes under an appropriate pressure (0.01 to several'forr). is supplied to produce a glow discharge, and the SiH
4 gas is decomposed to form an A-81 film on the substrate. On the other hand, methods that apply conventional vacuum evaporation methods, sputtering methods, etc., in which a portion of the gasified silicon is hydrogenated in the process until it reaches the substrate, are as follows. Using silicon as a target in a vacuum chamber, sputtering is performed by mixing hydrogen gas with an inert gas such as argon, and a part of the silicon atoms flying out from the target reacts with ionized hydrogen to form an A-81 film on the substrate. Silicon is heated and melted and evaporated using a so-called reactive sputtering method or an electron gun in a vacuum chamber, and some of it combines with hydrogen ionized by glow discharge from an RF coil during the flight process to the substrate. a- on the board
For example, a glow discharge type ion blating method is used to form a 81 film.

There are various other methods such as ionized cluster beam method, arc discharge type ion blating method, and photo-CVD method, but they can be roughly divided into two methods: supplying gas and removing hydrogen from the gas until the silicon becomes solid through decomposition; It can be divided into two methods: turning it into a gas, adding hydrogen to it and then solidifying it again. Furthermore, very recently, F
(Fluorine) can also be obtained, so instead of using SiH4 gas, a method of forming an a-8i film by glow discharge decomposition using SiF4 gas has been introduced, although it is somewhat difficult to handle.

As mentioned above, various methods for forming A-81 films whose conductivity type can be controlled have been developed and put into practical use, but all of these methods have various problems when manufacturing semiconductor devices. There is. Some of these problems are discussed below.

Plasma CVD method or photo CVD method uses 5IH4 gas or 8
1F4 gas, etc. is decomposed using electrical energy or light energy. When producing an a-8i film on a substrate, the gas pressure of the reaction gas is 1 atm (760 Torr).
), that is, in a considerably dilute gas atmosphere.

There is a limit to the gas supply rate, so the biofilm rate cannot be increased. In addition, since the decomposition of SiH4, SiF, and gases takes place in gas, the decomposition products have no directionality and are extremely inefficient in supplying to the substrate. It is no exaggeration to say that materials are being thrown away. Also, a-8 generated in a place other than the board
1 or by-products are large and in the form of fine powders and flakes, so if they fly, they degrade the film quality of the substrate and become an obstacle to continuous biofilm formation, so it is difficult to clean the inside of the reaction chamber. It requires a lot of effort and expense.

5IR4 gas is dangerous because it is spontaneously flammable, and
Since IF4 gas is corrosive upon decomposition, considerable expensive equipment is required for the supply, storage, exhaust gas treatment, etc. of these materials.

In the case of a method that does not use the above-mentioned gas, but instead vaporizes the solid silicon and partially hydrogenates or fluorinates it in the process of reaching the substrate, simply vaporizes the silicon and performs, for example, vapor deposition. It is relatively easy to increase the biofilm velocity if the film is simply deposited by the method, but in order to carry out hydrogenation or fluorination in a controlled manner, the biofilm velocity must be increased as in the case of using gases as described above. It is kept small. Additionally, for hydrogenation and fluorination, it is necessary to ionize hydrogen gas, but this requires energy greater than the decomposition energy of the gas, so ionization equipment must be large-scale. turn into. In order to increase the biofilm speed in the plasma CVD method, disilane (5hHs) is used instead of monosilane gas.
) It has been considered to use higher-order silane such as gas, but since it is extremely expensive, it is not practical from a practical point of view as long as the conventional glow discharge decomposition method is used, which is inefficient. It's not appropriate.

The present invention provides a completely new method for producing an a-Sl film that eliminates the above-mentioned problems, and produces an a-Sl film at an efficient biofilm rate with less wasteful consumption of raw materials using a relatively simple device.
The purpose of the present invention is to provide a method for obtaining an 8t film.

In the method according to the present invention, SiH4, S,..., IF
A- containing hydrogenated silicon or fluorinated silicon is once heated in a vacuum container using a conventional glow discharge decomposition method using 4 gases.
81 is generated. The purpose of the generation of a-3t at this time is not to fabricate devices by placing a substrate, but to generate a-8t containing solidified hydrogenated silicon (or fluorinated silicon) in the entire vacuum chamber. It is in the collection of. The produced and recovered A-8i is solidified and used as an evaporation source to form A-8 onto a substrate using a conventional vapor deposition method, ion blasting method, cluster beam method, etc. that has a high biofilm rate.
This is a method of producing an i-film.

Hereinafter, the present invention will be described in detail using a method for producing an a-8i film containing hydrogenated silicon as an example.

Generally, gaseous silicon compounds include monosilane (
Gases such as SiH4) and disilane (SizHa) are known and are produced to some extent industrially, but hydrogenated silicon in solid form (solid silicon containing a certain amount of hydrogenated silicon) can be produced using the glow discharge decomposition method described above. Although it can be obtained by such methods, it was not used as a raw material. Silicon hydride in the form of a solid can also be obtained by a wet chemical method using the above-mentioned SiH4 gas, Sl, H, gas, but a-8, which has a reduced localized level and can control the conductivity type.
Considering that the ultimate objective is to obtain a high elasticity, it is necessary to obtain hydrogenated silicon in the form of a solid with a controlled hydrogen content, making this method inappropriate.

The inventors were able to obtain solid silicon containing a controlled and appropriate amount of hydrogenated silicon by the conventionally used glow discharge decomposition (plasma CVD) method in a vacuum vessel using SiH4 gas. That is, by introducing 5tH4 gas into a vacuum container and controlling manufacturing conditions such as glow discharge power, degree of vacuum, molar ratio, and temperature of the reaction container, solid silicon hydride with a hydrogen content of 0 to 65% molar can be produced. could be easily obtained. An example of a method for obtaining this solid hydrogenated silicon is schematically shown in FIG. Silane gas is supplied from a cylinder 2 into a reaction vessel 1 which can be evacuated. In order to determine the conductivity type and the amount of impurities, a required amount of hydride (gas) such as N, P, As, B, etc. is supplied from the cylinder 3 in a predetermined amount. SiH4 gas is decomposed by glow discharge using a high frequency power source 4 and a high frequency coil 5 installed in the reaction vessel 1, and the generated powdered a-81 is stored in a storage tank 8 connected to a vacuum pump 6 and partitioned by a filter 7. It is.

A similar solid silicon hydride can also be obtained by introducing SiH4 gas during arc discharge.

Almost all of the produced solid silicon hydride can be recovered from within the vacuum container. However, the solid silicon hydride thus obtained is in the form of a fine powder with extremely small particle sizes, has a light liquid-like fluidity, and is easily dispersed by even a slight breeze, making it extremely difficult to handle. Therefore, as it is, it is not suitable as a material for vapor deposition or sputtering. In other words, if left as is, it will be easily scattered by changes in the airflow inside the container when it is evacuated, by the heat action for evaporation, or by the bombardment action during sputtering, so it must be solidified or agglomerated by some method. There is a need. This powder is stable in the air, but will ignite at about 600C, and once ignited, it will burn instantly and in large quantities it can be extremely dangerous, and will burn even more violently if water is poured over it. Furthermore, this powder is completely immiscible with water and cannot be kneaded with water. Although it can be dispersed in organic solvents such as alcohol, acetone, and trichlene, it is dangerous because it reacts with lower alcohols and generates flammable gas, hydrogen gas, etc., which may cause ignition, and the reaction may alter the quality of the raw materials. I end up.

As a result of various experiments, it was found that fluorocarbon solvents are suitable for solidifying and agglomerating this powdered solid hydrogenated silicon.

C, CL3Fm, etc. are often used as fluorocarbon solvents, and when this powder was mixed into these solvents, it immediately dispersed and became mud-like, and there was no scattering of the powder. Take out the kneaded material by stirring and make it into a thickness of 1m to 10m.
When the solvent was evaporated by drying, a completely solid plate was obtained.

When this solid substance is analyzed, only hydrogen and silicon are detected, and no carbon or halogen is detected.It is a stable solidified solid hydrogenated silicon that does not react with the solvent, has no residual solvent, and does not change the hydrogen content. I was able to get it. I found out that powdered silicon hydride can be solidified as described above.
This is pressed into an appropriate shape such as a pellet and used as a raw material and as an evaporation agent or target for vapor deposition sputtering.

FIGS. 2 and 3 schematically show these methods. FIG. 2 shows an example of an apparatus for the vacuum evaporation method, and FIG. 3 shows an example of an apparatus for the cluster beam method.

In FIG. 2, a substrate 12 that can be heated by a heater 11 is installed in a container 10 that can be evacuated by a vacuum pump 6, and the solidified silicon hydride 14 is placed in a container 16 opposite to the substrate 12. put. Then, the solid silicon hydride 14 is evaporated by the electron beam supplied from the electron gun 15 to form an A-81 film on the substrate 12. The substrate may be rotated to increase the uniformity of the resulting film.

In the tJ3 diagram, solidified hydrogenated silicon 14 is sealed in a crucible 16 that has pores with a designed size and aspect ratio, and is heated from the outside to increase the internal pressure of the crucible and ejected from the pores to provide insulation. Due to the supercooling effect caused by expansion, the a-81 film is clustered on the substrate 12. Note that an ionization source, accelerating electrode, etc. may be added to this.

In addition, in both of the devices shown in FIGS. 2 and 3, hydrogen gas is introduced from the outside to cause glow discharge.
It is also possible to readjust the amount of hydrogenated silicon contained in the 8i film.

Although an apparatus for sputtering is not shown, sputtering may be performed using the solidified solid hydrogenated silicon as a target.

As described above, according to the present invention, by using solid silicon containing hydrogenated silicon instead of solid silicon as a raw material such as an evaporation source or target, it is not necessary to introduce hydrogen gas from outside. In both cases, a high-quality a-8i film containing 1 to 40% hydrogen can be formed on a substrate at a speed comparable to that of conventional vacuum evaporation. Furthermore, according to the present invention, the recovery and usage efficiency of a-8t is much better than that of the conventional plasma CVD method, and since the conventional vacuum evaporation method can be used, the deposition efficiency is extremely high, and therefore the There are also very few by-products and workability is greatly improved.

Although the present invention has been described using hydrogenated silicon as an example, it goes without saying that it can also be applied to fluorinated silicon.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus for obtaining solid silicon hydride according to the present invention, and FIGS. 2 and 3 show an a- FIG. 2 is a schematic diagram showing an example of an apparatus using a vacuum evaporation method and a cluster beam method to obtain a 81 film. 1... Reaction container; 2, 6... Cylinder; 4... High frequency power supply; 5... High frequency coil; 6... Vacuum pump;
8... Storage tank; 10... Vacuum container; 12... Substrate; 14... Solidified solid hydrogenated silicon; 15...
・Electron gun; 16... Crucible. Patent applicant: Stanley Electric Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (4)

[Claims] (1) A method for producing an amorphous silicon film, which uses solid silicon containing silicon hydride or silicon fluoride as a raw material as a raw material, and produces an amorphous silicon film on a substrate in a low-pressure container that can be evacuated. (2) Production of an amorphous silicon film according to claim 1, wherein the amorphous silicon film is produced by any one of a vacuum evaporation method, an ion blating method, a cluster beam method, and a sputtering method. Law. (3) The method for producing an amorphous silicon film according to claim 1, wherein the solid silicon is obtained by a glow discharge decomposition method using gaseous hydrogenated silicon or a fluorinated silicon compound. (4) The solid silicon is solidified by dispersing powdered solid silicon in a fluorocarbon-based solvent and then evaporating the solvent to dry it. A method for producing amorphous silicon films.