JPS61241913A - Manufacture of gallium nitride film - Google Patents

Abstract

PURPOSE:To obtain a uniform gallium nitride film by reducing the pressure of an atmosphere exposing a substrate in a gas containing a compound which contains a gallium atom, then by reducing the pressure of the atmosphere exposing in ammonia or hydrazine gas and by irradiating ultraviolet rays each time. CONSTITUTION:A substrate is subjected to the repetition of the first process wherein the substrate is exposed in a gas containing a compound which contains a gallium atom, the second process of reducing the pressure of the atmosphere near the surface of the substrate, the third process of irradiating ultraviolet rays on the surface of the substrate reducing the pressure of the atmosphere, the fourth process of exposing the substrate in a gas containing ammonia or hydrazine, the fifth process of reducing the pressure of the atmosphere near the surface of the substrate and the sixth process of irradiating the ultraviolet rays on the surface of the substrate reducing the pressure of the atmosphere. A gas-state compound which contains the Ga atom and a non-oxidizing gas such as H2 or He are used for the gas containing a compound which contains the Ga atom. A mixture of NH3 or N2H4 and a non-oxidizing gas is used for a gas which contains NH3 or N2H4. This enables to obtain a gallium nitride film which has good film quality and uniform film thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a gallium nitride film that can be used for light emitting devices, field effect resistors, and the like.

BACKGROUND OF THE INVENTION Normally, a chemical vapor deposition method (CVO method) is exclusively used as a method for forming a high-quality gallium nitride (GaN) film (for example, Japanese Patent Laid-Open No. 140799/1983).

Problems to be Solved by the Invention However, in this case, the substrate temperature needs to be about 1000°C or higher,
Therefore, the production equipment becomes complicated, and the grown layer is subject to strain due to the difference in thermal expansion coefficient between the substrate and the gallium nitride (GaN) grown layer, which tends to cause peeling or the like. In addition, as a gallium (Ga) source, trimethyl gallium (T
In the chemical vapor deposition method using MG) or tri-ethyl gallium (TEG), the substrate temperature can be lowered slightly, but in order to obtain gallium nitride (GaN) with satisfactory properties,
A substrate temperature of 0° C. or higher is required. Films formed on substrates colder than this are unstable in air.

Means for Solving the Problems In order to solve the above problems, the method for producing a gallium nitride film of the present invention includes a first step of exposing the substrate to a gas containing a compound containing gallium atoms, and then the step of exposing the substrate to a gas containing a compound containing gallium atoms. a second step of reducing the pressure of the atmosphere near the substrate surface; a third step of irradiating the substrate surface with ultraviolet rays while reducing the pressure of the atmosphere near the substrate surface; a fourth step of exposing the substrate surface to a gas containing , a fifth step of reducing the pressure of the atmosphere near the substrate surface, and then applying ultraviolet light to the substrate surface while reducing the pressure of the atmosphere near the substrate surface. The sixth step of irradiation is repeated to obtain a gallium nitride film.

Effect It is assumed that the following phenomenon occurs in each step of the above method.

First, the substrate is made of trimethyl gallium (TMG; Ga (
CI(,):l) or tri-ethyl gallium (TE
The first step is exposed to a gas containing G; Ga(C2H,)i), etc.
In the process, an adsorption layer consisting of one to several molecular layers of trimethyl gallium (TMG; Ga(CIla)a) molecules or triethyl gallium (TEG; Ga (C2H,)3) molecules is formed on the substrate surface. is formed.

Next, in the second step of reducing the pressure of the atmosphere near the substrate surface, the adsorption layer on the substrate surface is removed, and tri-methyl gallium (TMG; Ga
(C)13)3) or tri-ethyl gallium (
The gas containing TEG; Ga (C2Its)3) is exhausted and removed.

Next, in a third step of irradiating the substrate surface with ultraviolet light while continuing to reduce the pressure of the atmosphere near the substrate surface, the ultraviolet light is absorbed by the adsorption layer. Tri-methyl gallium (TMG: Ga) adsorbed by this light energy and thermal energy derived from substrate heating
(CH3)3) Tri-ethyl gallium (T
UG; Ga(C,H5)3) molecules decompose and form gallium (
Ga) atoms are precipitated. At this time, the ultraviolet light is emitted because the gas near the substrate surface is depressurized and exhausted.
It is believed that the adsorption layer is efficiently reached.

Next, the substrate is treated with ammonia (NH3) or hydrazine (
In the fourth step of exposing to a gas containing N2H4),
An adsorption layer consisting of one to several molecular layers of ammonia (N) I, ) molecules or hydrazine (N2 H4) molecules is formed on the surface of the substrate.

Next, in the fifth step of reducing the pressure of the atmosphere near the substrate surface, the adsorption layer on the substrate surface is removed, and ammonia (NH3) or hydrazine (hydrazine) near the substrate surface is removed.
The gas containing N2H4) is evacuated and removed.

Next, in a sixth step of irradiating the substrate surface with ultraviolet light while reducing the pressure of the atmosphere near the substrate surface, the ultraviolet light is absorbed by the adsorption layer. This light energy and the thermal energy derived from substrate heating are used to generate adsorbed ammonia (N) molecules or hydrazine (N) molecules.
to4) The molecules decompose, thus depositing a monolayer, or a film spanning several molecules, of gallium nitride. In addition, at this time, the said ultraviolet light is.

Since the gas near the surface of the substrate is depressurized and exhausted, it is thought that it efficiently reaches the adsorption layer.

Note that when carrying out the above method, trimethyl gallium (TMGS) is used as a compound containing a gallium atom.
Ga(CH3)3) or tri-ethyl gallium (T
EG; Ga(C,H5)3'') is used.
This is desirable because the device is simple. These compounds are liquids at room temperature, and therefore are always used diluted with non-oxidizing gas.

Gases containing compounds containing gallium (Ga) atoms include gaseous compounds containing m atoms of gallium (Ga) and non-oxidizing compounds such as hydrogen (11□), helium (He), or argon (Ar). Use gas.

Ammonia (NH3) or hydrazine (Nil(4)
) A mixture of ammonia (NH3) or hydrazine (N2H, ) and the non-oxidizing gas is used.

There are no particular restrictions on the material of the substrate as long as the surface has good flatness.The cheapest and most desirable substrate is a quartz substrate or a glass substrate coated with a crystalline aluminum oxide film. When the present invention was carried out at a substrate temperature of 650° C., X-ray diffraction experiments of the film showed that the crystalline aluminum oxide film using the crystalline aluminum oxide film as a coating on the substrate had the best crystallinity.

This film can be formed by sputtering.

The temperature of the substrate needs to be 500°C or higher. If the substrate temperature is lower than this, the formed film will have a low refractive index and may be unstable even in air.

When the substrate temperature is raised to 750° C. or higher, the uniformity of the film thickness tends to deteriorate.

A heater or the like is used to maintain the substrate at a temperature higher than room temperature.

A cryo pump or a mechanical booster pump is usually used to reduce the pressure of the atmosphere near the surface of the substrate. The ultimate degree of vacuum needs to be at least about 10' Torr.

Desirable ultraviolet light sources include excimer lasers, low-pressure mercury lamps, and xenon lamps, but among these, low-pressure mercury lamps are most desirable from the viewpoint of ease of handling.

For example, a lens made of synthetic quartz is used in the optical system for condensing the ultraviolet light. Further, in the manufacturing apparatus used for carrying out the method for manufacturing a gallium nitride (GaN) film according to the present invention, the window for introducing the ultraviolet light is formed of, for example, synthetic quartz. Further, by constantly spraying pure hydrogen or pure argon to prevent the window from fogging up with precipitates, it is possible to prevent the compounds, ammonia (NH3), or hydrazine (N, H4) from adsorbing to the window.

Example Embodiments of the present invention will be described below based on the drawings.

The drawing is a cross-sectional view of a manufacturing apparatus used to carry out a method for manufacturing a gallium nitride film in an embodiment of the present invention, and 1 is a 100W
2 is a shutter, 3 is a synthetic quartz lens, 4 is an ultraviolet light passage, 5 is a reaction chamber,
6 is a window made of synthetic quartz, 7 is a base carrier with a built-in heater, 8
9 is a base, 9 is a pipe for spraying pure Album onto the window 6 to prevent it from fogging up, and 10 is trimethyl gallium (TMG; Ga(CH3)a ) or triethyl gallium.
Piping 11 is for supplying gas containing gallium (TEG; Ga(c+H5L)), 11 is ammonia (NH3
) or hydrazine (Nw H4), 12 is a pipe for suctioning the argon gas supplied from pipe 9, 13 is pipe to, 11
Piping for sucking gas supplied from 14 to 16
is a solenoid valve, 17 is a mechanical booster pump, 1
8 is a cooling corrugated pipe. In addition, the reaction chamber 5 has piping 9 to 13.
Strict consideration was given to ensure that there is virtually no leakage of outside air into the interior.

Next, the manufacturing procedure will be explained. As the base 8.

A quartz glass, a quartz glass coated with crystalline aluminum oxide by a sputtering method, and a silicon (Si) crystal plate were used. When carrying out the sputtering method, quartz glass is
Heated to 0°C. The presence or absence of crystallinity of the formed aluminum oxide was examined by X-ray diffraction. After washing and drying these substrates 8, they are further placed in the reaction chamber 5 of the manufacturing apparatus and heated with a heater in the substrate carrier 7.
It was kept at about 600°C for 1 hour. At this time, the reaction chamber 5 was preliminarily evacuated using a separately provided oil rotary pump (not shown), and then the reaction chamber 5 was evacuated using a separately provided cryo pump (not shown) to maintain a reduced pressure state. . While maintaining the reduced pressure, the temperature of the substrate 8 was lowered to 500° C., and thereafter maintained at this temperature during the formation of the gallium nitride film.

The ultimate degree of vacuum at this time was approximately 10'aTorr.

Next, the mechanical booster pump 17 was operated to keep the reaction chamber 5 in an evacuated state, and a gallium nitride film was formed by the following steps.

First, open the solenoid valve 15 and use trimethyl gallium (T).
MG; Ga (CH-)3) containing argon (
Ar) approximately 10- was introduced in the vicinity of the substrate 8. At the same time, the solenoid valve 14 is opened and about 30 cd of pure argon (A'
) was introduced and sprayed on window 6. The time required for this step was about 0.5 seconds. After this, solenoid valves 15 and 14
and closed in this order.

Next, the air was evacuated for about 1.5 to 5 seconds. At this time, the degree of vacuum in the reaction chamber 5 was about 10'Torr. Then, the shutter 2 accompanying the ultraviolet light source 1 consisting of a 100 W low-pressure mercury lamp was opened, and the substrate 8 was irradiated with the concentrated ultraviolet light for 1 second.

Next, the electromagnetic valve 16 was opened, and about 10 cd of argon (Ar) containing 20% ammonia (NH) was introduced into the vicinity of the substrate 8. At the same time, open the solenoid valve 14 and
AJ of pure argon (Ar) was introduced and blown to $6.

The time required for this process was about 0.5 seconds. After that, the solenoid valves 16 and 14 were closed in this order.

Next, the air was evacuated for about 1.5 to 5 seconds. At this time, the degree of vacuum in the reaction chamber 5 was about 10'Torr. Then, the shutter 2 accompanying the ultraviolet light source 1 consisting of a 100 V low-pressure mercury lamp was opened, and the substrate 8 was irradiated with the concentrated ultraviolet light for 1 second.

The above procedure was repeated to obtain a gallium nitride film. The identity of the gallium nitride film was determined by the refractive index of the film. When the number of repetitions was about 400, the thickness of the formed gallium nitride film was about 1,700. As a result of an electron diffraction experiment of the formed gallium nitride film, it was found that the film was amorphous. 6 However, when quartz glass coated with crystalline aluminum oxide was used as the substrate 8, some crystallization was observed. Furthermore, when the refractive index of the gallium nitride film was measured using an Esopri meter when a silicon (Si) crystal plate was used as the substrate 8, the value was 2.3.
It was 8. This value corresponds to the commonly known refractive index of gallium nitride, 264.

According to the conventional chemical vapor deposition (CVD) method, the refractive index is 2.3.
In order to obtain the above gallium nitride film, a substrate temperature of 1000° C. or higher is required.

Regarding the uniformity of the thickness of the formed gallium nitride film,
Although it varied slightly depending on the type of substrate 8, the difference in film thickness was within 1% for two substrates 8 placed 10 holes apart. According to the conventional method, this value can be achieved by increasing the size of the device, but there is also a limit to this, and therefore it is a value that is quite difficult to reach. The film thickness was measured using a step needle and by observing the cross section using a scanning electron microscope.

Next, a second embodiment will be described. The manufacturing equipment is the first
The same one as in the example was used, but as the ultraviolet light source 1,
IKW xenon lamps were used. As the base 8, the same one as in the first example was used.

First, these substrates 8 were washed and dried, and then placed in the reaction chamber 5 of the apparatus, heated by the heater of the substrate carrier 7, and kept at about 600° C. for 1 hour. At this time, the reaction chamber 5 was preliminarily evacuated using a separately provided oil rotary pump (not shown), and then the reaction chamber 5 was evacuated using a separately provided cryo pump (not shown) to maintain a reduced pressure state. . The ultimate degree of vacuum at this time was about 104 Torr. After that, this temperature was maintained during the formation of the gallium nitride film.

Next, from then on, the mechanical booster pump 17 was operated to keep one reaction chamber 5 constantly in an evacuated state, and a gallium nitride film was formed by the following steps.

That is, first, open the solenoid valve 15, and from the pipe lO,
Tri-ethyl gallium (TMG; Ga (cz H
Argon (Ar) containing about 3% of s)3) about 15ad
was introduced near the substrate 8. At the same time, the solenoid valve 14
The window 6 was opened and about 30 aif of pure argon (Ar) was introduced and blown onto the window 6.

The time required for this process was about 0.5 seconds. After this, the solenoid valves 15 and 14 were closed in this order.

Next, the air was evacuated for about 1.5 to 5 seconds. At this time, the degree of vacuum in the reaction chamber 5 was about 10'Torr6, and the light was on. The shutter 2 associated with the ultraviolet light source 1 consisting of an LK1 xenon lamp was opened, and the substrate 8 was irradiated with focused ultraviolet light for 1 second.

Next, open the solenoid valve 16 and pour about 15 c of argon (Ar) containing 5% hydrazine (N2 H4) from the pipe 11.
d was introduced near the substrate 8. At the same time, solenoid valve 1
4 and introduced about 30-pure argon (Ar).
I sprayed it on window 6. The time required for this process was about 0.5 seconds. After that, the solenoid valves 16 and 14 were closed in this order.

Then, the air was evacuated for about 1.5 to 5 seconds. At this time, the degree of vacuum in the reaction chamber 5 was about 10'Torr. Then, the shutter 2 accompanying the ultraviolet light source 1 consisting of 1) [11 xenon lamps that are lit is opened, and the base 8
Ultraviolet light focused on was irradiated for 1 second.

The above procedure was repeated to obtain a gallium nitride film. The identity of the gallium nitride film was determined by the refractive index of the film. When the number of repetitions is approximately 400.

The thickness of the formed gallium nitride film was approximately 1,600 mm. As a result of an electron diffraction experiment of the formed gallium nitride film, it was found that the film was crystallized to some extent. In particular, when the substrate 8 was made of quartz glass coated with crystalline aluminum oxide, the degree of crystallization was good. Further, when the substrate 8 is a silicon (Si) crystal plate, the refractive index of the gallium nitride film formed thereon was measured with an Ethopri meter, and the value was 2.43.

Regarding the uniformity of the thickness of the formed gallium nitride film,
Although it varies slightly depending on the type of substrate 8, the difference in film thickness was within 1% for two substrates 8 that were placed apart from each other.

According to the present invention, a gallium nitride film having good film quality and uniform thickness can be obtained at low temperatures. therefore.

It makes an extremely large contribution to the production of thin film transistors and light emitting devices.

[Brief explanation of the drawing]

The drawing is a cross-sectional view of a manufacturing apparatus used to carry out a method for manufacturing a gallium nitride film in an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Ultraviolet light source, 8... Base|substrate, 10... Piping for supplying the gas containing the compound containing a gallium atom. 11... Piping for supplying gas containing ammonia or hydrazine

Claims (1)

[Claims] 1. A first step of exposing the substrate to a gas containing a compound containing a gallium atom, a second step of reducing the pressure of the atmosphere near the surface of the substrate, and then a step of exposing the substrate to a gas containing a compound containing a gallium atom. a third step of irradiating the surface of the substrate with ultraviolet rays while reducing the pressure of the atmosphere near the substrate; a fourth step of exposing the substrate to a gas containing ammonia or hydrazine; A gallium nitride film is obtained by repeating a fifth step of reducing the pressure of the atmosphere and a sixth step of irradiating the surface of the substrate with ultraviolet light while reducing the pressure of the atmosphere near the surface of the substrate. Production method. 2. As a compound containing a gallium atom, trimethyl
A method for manufacturing a gallium nitride film according to claim 1, using gallium. 3. As a compound containing a gallium atom, tri-ethyl-
A method for manufacturing a gallium nitride film according to claim 1, using gallium. 4. A method for manufacturing a gallium nitride film according to any one of claims 1 to 3, in which the substrate is coated with a crystalline aluminum oxide film.