JPS60126822A - Method and apparatus for optical vapor growth - Google Patents

Abstract

PURPOSE:To enable to perform continuously projection of light, to enable to curtail film forming time, and moreover to enable to form a crystalline film of favorable quality by a method wherein formation of film onto a light introducing window or the surface of the wall of a light source is checked or reduced. CONSTITUTION:A substrate holder 2 provided with a heater is set up inside of a reaction chamber 1, and a substrate 3 is arranged thereon. Incident light 5 projected from a light source provided outside is introduced into the reaction chamber 1 through a light introducing window 4. A lattice 6 manufactured of a metal thin plate is provided between the light introducing window 4 and the substrate holder 2. The lattice 6 thereof is fixed to a ring type vessel 7, and cooled according to conduction of heat when a refrigerant is put therein. Raw material gas and a mercury sensitizer are introduced into the reaction chamber 1 from a gas introducing port 8 provided on the substrate side than the lattice 6. A purging gas introducing port 9 is provided on the light introducing window side than the lattice 6, and purging gas is exhausted from an exhaust vent 10 together with the raw material gas through gaps between the lattice 6. The substrate holder 2 is rotatable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a photovapor phase growth method and a photovapor phase growth apparatus.

[Technical background of the invention and its problems]

Since the optical vapor phase epitaxy method uses photon energy to decompose the source gas, the temperature of the substrate may be lower than that in the normal vapor phase epitaxy method. Therefore, this method is expected to be an effective film forming method for lowering the temperature of Zorrothe in the semiconductor industry. Furthermore, since the method does not use charged particles in principle, the formed film is not damaged, and it is considered to be a particularly effective method for forming structurally sensitive semiconductor films such as amorphous silicon films.

Although the optical vapor phase epitaxy method has the above-mentioned characteristics, there are problems caused by film formation on the light introduction window. The target film, except for some insulating films, is opaque to the wavelength of the light used.
The light intensity in the reaction chamber decreases with the time of light irradiation. Due to this problem, frequent cleaning of the light introduction window is required, and in severe cases, it may not be possible to obtain a sufficient film thickness with one light irradiation, so cleaning and light irradiation of the window 7 may be repeated several times. A film with the required thickness is formed.

Efforts have been made to form an amorphous silicon film to prevent the substrate from being exposed to the outside air, except through a window fN This clearly limits the types of films that can be formed by photovapor phase growth.

On the other hand, when the wavelength of the light used is in the vacuum ultraviolet range, the type of light introduction window is restricted. Lithium fluoride window is 105 nm
However, the mechanical strength is low, and creating a large-area window causes problems such as complicating the device.

In order to use even shorter wavelength light, it would be better if the light could be introduced directly from the light source without a window, but this would cause raw material gas to enter the light source and form a film on the wall of the light source, making the discharge unstable. Problems such as oxidation occur.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for optical vapor phase growth that solves the above-mentioned problems by preventing or reducing film formation on the light introduction window or the wall surface of the light source section.

[Summary of the invention]

In the photovapor phase growth method, two methods are used: (1) decomposition of the raw material gas by direct light; and (2) indirect decomposition by mixing a photosensitizer with the raw material gas and colliding with atoms or molecules of the sensitizer excited by light irradiation. There is a method to decompose raw material gas. In order to suppress film formation at the light introduction window, it is sufficient that the concentration of the raw material gas is low in the case of (1), and the concentration of the sensitizer in addition to the raw material gas is low in the case of (2) near the window.

In other words, it is sufficient that the density of gas atoms or molecules essential for thin film formation is sufficiently low near the window.

Based on the above findings, in the present invention, an object that does not impede light transmission is placed on the light source side of the substrate in the reaction chamber. The surface of this object is given a function to physically or chemically adsorb the gas essential for forming the thin film. The gas essential for film formation is usually introduced into the substrate side of the object placement section.

Now, gas atoms or molecules essential for film formation diffuse through the space between the objects from the substrate side to the light introduction window side. Since the surface of the object adsorbs this gas, in the space between them, the gas also diffuses from the center of the space toward the surface of the object, so the distance between the surfaces and the length of the surface in the direction of light introduction must be set appropriately. As a result, most of the gas essential for film formation can be adsorbed onto the surface of the object in the process of diffusing toward the light introduction window.

In order to adsorb gases essential for film formation on the surface of an object,
The following three methods are effective.

The first method is to raise the temperature of the object surface to a temperature sufficient to decompose the source gas and form a film on the surface. The second method is to cool the surface to a temperature where the vapor pressure of the gas essential for thin film formation is sufficiently low compared to the partial pressure near the substrate, and condensation of other gases can be ignored. This method is particularly effective in the case of mercury sensitization, and by appropriately selecting the type of raw material gas and the cooling temperature, it is possible to selectively condense only mercury onto the surface of the object. The third method is to use a substance that selectively adsorbs the raw material gas or the sensitizer as the material of the object or the surface material.

As mentioned above, the gas essential for film formation can be trapped in the object placement part and can be made difficult to reach the light introduction window, but what is particularly effective is the use of photosensitizers as gases essential for film formation. This is the case. This is because the sensitizer usually has a lower partial pressure than the raw material gas, and only a small amount is trapped on the surface. On the other hand, when considering the raw material gas as an essential gas for film formation, problems may arise, such as the amount of traps being large and the trapping effect not being perfect, if left as described above. Therefore, creating an airflow from the light introduction window side to the substrate side is effective in suppressing film formation on the window. Such an air flow may be created by introducing a gas inert to the photochemical reaction into the light introduction window, or alternatively, a gas that does not directly photodecompose among the raw material gases may be introduced.

The above-mentioned method of creating a trap on the surface of an object and an air flow passing between objects is not limited to devices in which the light source is placed outside the reaction chamber with a light introduction window, but also in devices in which the light source is placed directly inside the reaction chamber and has a light introduction window. It can also be applied to photo-vapor phase growth equipment that does not have a

This device without a light introduction window is particularly effective when the pressure in the light source section and the pressure in the substrate placement section are approximately the same or the pressure on the light source section side is high.

〔Effect of the invention〕

According to the present invention, since film formation on the light introduction window is prevented or reduced, light irradiation can be performed continuously. As a result, the film formation time can be shortened compared to a method in which the cleaning ratio of the light introducing window and the film deposition are repeated. Furthermore, since there is no need to interrupt film formation, a film with sufficient thickness and good characteristics can be obtained with few impurities in the formed film. Furthermore, if film formation is interrupted when forming a crystalline film, nucleation may be inhibited, but according to the present invention, crystallization occurs favorably and, as a result, a crystalline film of good quality is obtained.

Furthermore, in a photo-vapor phase growth apparatus without a light introduction window, film formation at the light source can be prevented or reduced. As a result, when the light source section is operated by microwave discharge, changes in discharge conditions are reduced.

[Embodiments of the invention]

FIG. 1 shows an apparatus according to an embodiment of the present invention.

(-) is a longitudinal cross-sectional view, and (b) is a cross-sectional view at the A-A' position. In the figure, 1 is a reaction chamber, in which a heating heating substrate holder 2 is provided, and a substrate 3 is placed on top of it. 4 is a light introduction window, and a light source provided outside. The irradiation light 5 from a (not shown) is guided into the reaction chamber 1 through the light introduction window 4.

A grid 6 made of a thin plate of metal, for example oxygen-free copper, is provided between the light introduction window 4 and the substrate holder 2. This grid 6 is fixed to a ring-shaped container 7 containing a refrigerant, so that it can be cooled by heat conduction. The raw material gas and the mercury sensitizer are introduced into the reaction chamber 1 through a gas inlet 8 provided closer to the substrate than the grid 6 . There is still a purge gas inlet 9 on the light introduction window side of the grating 6, and the purge gas passes between the grates 6 and is exhausted from the exhaust port 10 together with the raw material gas. The substrate holder 2 is rotatable to improve the uniformity of light irradiation.

In this apparatus, monosilane was used as a raw material gas, and an amorphous silicon film could be formed by irradiating ultraviolet light with wavelengths of 254 nm and 185 nm using a low-pressure mercury lamp as a light source. Hydrogen was used as a purge gas. The refrigerant was low-temperature nitrogen gas made by evaporating liquid nitrogen, and the temperature of the grid 6 was set at -50°C. The vapor pressure of mercury is 10''-6 Torr, which is sufficient to adsorb onto the grid 6, and monosilane, which has a boiling point of -111.9°C, is hardly condensed.

In the above embodiment, the grid 6 was cooled by a refrigerant, but any cooling method may be used, for example, an electronic refrigerator may be used. Furthermore, if the grating 6 has a large light transmission area, it may not be possible to sufficiently cool the central portion. To solve this problem, it is recommended to make the grid thicker, or weld thin pipes to form a grid, and allow the coolant to flow through the pipes, although this will reduce the light transmission area. In this case, it is particularly effective to rotate the substrate holder to obtain a uniform film.

Furthermore, as the purge gas introduced from the gas inlet 9 located on the side of the light introduction window 4 from the grid 6, monosilane gas may be used after being separated at the above-mentioned grid temperature.

In this case, the raw material is rather uniform on the substrate 3, which is effective in improving the uniformity of the film thickness.

Alternatively, hydrogen may be used as the gas, and trimethylsilane gas, which is not mixed with mercury gas, may be introduced from the gas inlet 8 as the raw material gas.

FIG. 2 shows another example device corresponding to FIG. 1.

In FIG. 1, gas is adsorbed using a cooled grid 6, whereas in FIG. 2, gas is adsorbed by heating a thin plate and forming a film thereon.

A spiral tungsten plate heater 11 is provided between the substrate 3 and the light introduction window 40, and a current is passed between the center and the outer periphery of the heater 11 to perform electrical heating. This equipment was used for film formation using fusilane as a raw material gas. The heating temperature of the heater 11 was approximately 400°C.

The purge gas introduced from the gas inlet 9 is hydrogen at 2 NO/
It's more than rnjn. This configuration is particularly effective when the raw material gas decomposition temperature is relatively low.

In addition to the heater 11, a thin plate welded with a sheath heater or a thin plate heated by spinning can be used in place of the heater 11.

The pond water invention can be implemented with various modifications. For example, in FIG. 1(,), the grating 6 may be divided into an upper grating and a lower grating at the position A-A' in the figure, and may have a two-stage fc structure. Furthermore, at this time, without being identified to one ring-shaped container 7,
Two ring-shaped containers 7 may be provided corresponding to each other, with the upper stage being liquid nitrogen and the lower stage being water-cooled. If you do it like this,
The influence of radiant heat from the board can be ignored.

In addition, the substrate holder may be made to revolve or revolve around itself.
It is also possible to reciprocate in directions that intersect at 5° (indicated by B in FIG. 1). Furthermore, the grid 6 may be not only cross-shaped but also nest-shaped, and furthermore, a large number of thin plates arranged side by side in a striped pattern may be used instead of the grid 6.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an apparatus according to one embodiment of the present invention, and FIG. 2 is a diagram showing an apparatus according to another embodiment. I...Reaction chamber, 2...Substrate holder, 3...Substrate,
4... Light introduction window, 5... Irradiation light, 6... Grid (gas adsorption object), 7... Ring-shaped container, 8... Raw material gas inlet, 9... Purge gas inlet , 1o...Exhaust port, 11...Plate heater (gas adsorption object). Figure 1 Figure 2 (b)

Claims (5)

[Claims] (1) In a photovapor phase growth method in which a raw material gas is introduced into a reaction chamber and light is irradiated to decompose the raw material gas through a photochemical reaction to form a thin film on a substrate, a portion of the reaction chamber is placed closer to the light source than the substrate. A photovapor phase growth method characterized in that photovapor phase growth is performed by providing an object that adsorbs gas atoms or molecules essential for forming a thin film so as not to impede the transmission of light. (2) In a photo-vapor phase growth apparatus that introduces a raw material gas into a reaction chamber and irradiates light to decompose the raw material gas through a photochemical reaction to form a thin film on a substrate, the light source side of the reaction chamber is closer to the substrate. A photo-vapor phase growth apparatus characterized in that an object is provided to adsorb gas atoms or molecules essential for thin film formation so as not to impede transmission of light. (3) The optical vapor phase growth apparatus according to claim 2, wherein the object physically adsorbs gas atoms or molecules. (4) The optical vapor phase growth apparatus according to claim 2, wherein the object chemically adsorbs gas atoms or molecules. (5) The optical vapor phase growth apparatus according to claim 2, wherein a gas flow is created from the light source side toward the substrate side through the gap between the objects.