JPH04111420A - Method and apparatus for crystal growth of semiconductor thin film crystal formation and device - Google Patents

Abstract

PURPOSE:To reduce an amount of carbon impurities greatly and to enable formation of a semiconductor thin film of good quality at a low substrate temperature by providing a thermal decomposition mechanism of organic metal and by supplying metallic atom produced by decomposition to a substrate. CONSTITUTION:A reactor 6 having an evacuation device 8 and a substrate heating device 6d is provided with heat decomposition mechanisms 6a, 6b. A hydrogen gas supply device 1 is connected to an organometallic bubbler 2 which is charged with organic metal through a flow rate controller 5. The organometallic bubbler 2 is connected to the reactor through the first thermal decomposition mechanism 6a. A V hydride supply device 4 is connected to the flow rate controller and the reactor through the second thermal decomposition mechanism 6b. Thereby, organometallic gas is decomposed into a metal which is a constituent element of a compound semiconductor and hydrocarbon when heated in hydrogen air flow. The metal is supplied onto a substrate in the form of metallic atom and hydrocarbon is discharged outside the reactor together with carrier gas. Therefore, supply of carbon impurities into a semiconductor thin film reduces, thereby realizing a semiconductor thin film of high purity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for growing thin film crystals of compound semiconductors.

(Prior Art) To fabricate various semiconductor devices using compound semiconductors, it is necessary to fabricate a thin film of the compound semiconductor on a semiconductor substrate. The quality of this thin film greatly affects the characteristics of the device.

Therefore, it is desirable to reduce the amount of impurities other than those intentionally mixed in to control conductivity.

Since impurities in compound semiconductors easily diffuse within solids,
When crystal growth is performed at high temperatures, the distribution of impurities is disturbed due to the diffusion of impurities, and the fine structure is destroyed. Therefore, it is desirable to perform crystal growth at a low temperature.

Techniques for growing compound semiconductor thin films include a vapor phase growth method using an organic metal (hereinafter referred to as MOCVD method) and a molecular beam method using an organic metal (hereinafter referred to as MOMBE). When heated, the group (2) organometallic gas decomposes into metals, which are constituent elements of compound semiconductors, and hydrocarbons. The other constituent element (I[[-In group V compound semiconductors, group II element, I[
- In group VI compound semiconductors, group Ⅰ elements) are supplied to the reactor in the form of hydrides or organic compounds, but elemental elements are also produced by thermal decomposition.

In conventional methods such as MOCVD and MOMBE, both source gases are supplied with thermal energy from the semiconductor substrate and are decomposed in the gas phase or on the surface of the substrate. Since the thermal energy supplied is determined by the temperature of the substrate,
When crystal growth is performed at low temperatures, the supply of thermal energy is insufficient, resulting in a low decomposition rate of the raw material gas. In crystal growth at low temperatures, a large amount of raw material gas needs to be supplied in order to have a sufficient amount of constituent elements present on the surface of the substrate. Therefore, even in the conventional method, when a hydride is used as a raw material, a reactor may be provided with a mechanism for thermally decomposing the hydride.

If an insufficiently decomposed organometallic gas is present on the substrate surface during crystal growth, carbon, which is a constituent element of the organometal, is incorporated into the semiconductor thin film. Carbon incorporated into a semiconductor behaves as an impurity.

Conventional methods cannot control the thermal decomposition of organic metals,
It has been difficult to reduce the amount of carbon impurities.

(Problem I that the invention seeks to solve) In conventional thin film crystal growth methods for compound semiconductors (MOCVD method and MOMBE method) using organic metals as raw materials, when crystal growth is performed at low temperatures, it is difficult to supply thermal energy. Due to the shortage, the decomposition rate of the raw material gas becomes low. In crystal growth at low temperatures, a large amount of raw material gas needs to be supplied in order to have a sufficient amount of constituent elements present on the surface of the substrate. Furthermore, carbon is incorporated into the semiconductor thin film from organic metals that are not sufficiently decomposed and acts as an impurity.An object of the present invention is to improve the utilization efficiency of raw material gas and reduce the amount of impurities.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for growing a thin film crystal on a compound semiconductor substrate using an organometallic gas as at least one of the raw materials in a reaction vessel. The gist of the invention is a semiconductor thin film crystal growth method characterized by providing equipment for thermally decomposing a gas, and using the equipment to decompose an organometallic gas and supplying it to the substrate surface in the form of pure metal molecules. It is something to do.

Further, the present invention provides a thermal decomposition mechanism in a reactor having an exhaust device and a substrate heating device, and a hydrogen gas supply device is connected to an organic metal bubbler filled with an organic metal via a flow rate controller. is connected to the reactor via the first pyrolysis mechanism, and the group hydride supply device is connected to the reactor via the flow controller and the second pyrolysis mechanism. The gist of the invention is a semiconductor thin film crystal growth apparatus having characteristics.

In conventional methods, the energy required to decompose the raw material is supplied from the semiconductor substrate and determined by the temperature of the substrate. 1& Even when the temperature of the board is kept low,
If the thermal energy necessary for decomposition can be supplied to the raw material gas molecules, the utilization efficiency of the raw material gas will be improved and carbon impurities will be reduced. The thermal decomposition is controlled by independently supplying thermal energy.

(Function) When the organometallic gas is heated in a hydrogen stream, it is decomposed into metals, which are the constituent elements of the compound semiconductor, and hydrocarbons. In conventional methods such as MOCVD method and MOMBE method,
Due to thermal energy supplied from the semiconductor substrate in this decomposition reaction, the constituent elements generated by the zero decomposition proceeding on or near the substrate are precipitated on the substrate to form a semiconductor thin film crystal.

In the present invention, by providing a thermal decomposition mechanism and supplying thermal energy, the organic metal is decomposed at a location away from the substrate. The organometallic decomposes to produce metals and hydrocarbons; the metals are supplied onto the substrate in the form of metal atoms, and the hydrocarbons are exhausted out of the reactor along with the carrier gas. Therefore, since the amount of organic metal that is not completely decomposed reaches the substrate surface is reduced, the incorporation of carbon impurities into the semiconductor thin film is reduced, and a highly pure semiconductor thin film can be obtained.

(Example) Next, an example of the present invention will be described. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention.

FIG. 1 shows a schematic diagram of a crystal growth apparatus according to the semiconductor thin film crystal growth method of the present invention. FIG. 0 shows an apparatus for growing compound semiconductor thin film crystals using organometallic and V-hydrogenated material gases. In FIG. 1, reference numeral 1 denotes a high-purity hydrogen gas supply device that supplies high-purity hydrogen gas as a carrier gas. 2 is an organic metal gas bubbler, which is filled with an organic metal that is liquid at room temperature. 3 is a constant temperature layer, which is used to maintain the organometallic bubbler at a constant temperature. 4 is a hydride cylinder, which is connected to piping via a pressure regulator. Flow rate controller 5 for hydrogen, organometallic, and hydride
is supplied to the reactor at a constant flow rate. 6 is a reactor, the main components of which are as follows. 5
a indicates a metal gas pyrolysis mechanism, 6b indicates a hydride pyrolysis mechanism, 6c indicates a pressure gauge, and 6d indicates a semiconductor substrate heating mechanism.
Place the semiconductor substrate 7 on this semiconductor substrate heating mechanism,
Reference numeral 8 is a vacuum evacuation device for thin film crystal growth, and valves are omitted in Figure 0 for evacuating the inside of the reactor. The present invention is characterized by having a metal gas thermal decomposition mechanism as shown in 6a.

GaAs thin film crystal growth was performed using the apparatus shown in FIG. Trimethyl gallium was used as a Ga raw material, arsine was used as an As raw material, and hydrogen was used as a carrier gas. Trimethyl gallium is an organic metal often used for compound semiconductor crystal growth, but ms grown by conventional methods using trimethyl gallium has a relatively high thermal decomposition temperature.
The film crystal contains a large amount of carbon as an impurity.

Figure 2 shows the relationship between the temperature of the organometallic thermal decomposition mechanism and the concentration of carbon incorporated into the GaAs thin film.The horizontal axis is the temperature of the organometallic thermal decomposition mechanism, and the vertical axis is the temperature of the grown thin film crystal. This is the concentration of carbon impurities included.

The temperature of the thermal decomposition mechanism of the group (2) raw material was approximately 800°C, and the temperature of the substrate during crystal growth was maintained at 500°C. The molar ratio of the supplied M-group raw material and V-group raw material was 1:3.5.

In FIG. 2, the case where the temperature of the organic metal thermal decomposition mechanism is set to room temperature and the organic metal is not decomposed corresponds to the conventional method in which a thermal decomposition mechanism of arsine, which is a group (Ⅰ) raw material, is provided. fi grown under conditions equivalent to the conventional method [film crystal has 101
Although carbon is contained at a high concentration higher than @c, -ff, the carbon concentration is reduced to about 1/100 by decomposing the organic metal by the organometallic thermal decomposition mechanism 6a.

This indicates that the amount of insufficiently decomposed organic metal reaching the surface of the growing substrate is decreasing, indicating that the thermal decomposition mechanism is functioning effectively. In addition, ■
The thermal decomposition mechanism temperature of group raw materials is approximately 700℃~approximately 1
000″C is used.

When the temperature of the thermal decomposition mechanism of the group material and the organic metal is 800°C and 1000'C, respectively, the substrate temperature is 400°C.
Even under relatively low temperature growth conditions for GaAs crystal growth, a thin film crystal with few impurities can be obtained, and the present invention is also effective in lowering the substrate temperature during crystal growth.

Comparing the decomposition temperatures of organometallic gases used for semiconductor crystal growth, trimethylgallium has a higher thermal decomposition temperature.
It was confirmed that trimethyl gallium was effectively decomposed in this example. Other organometallic gases can also be decomposed and supplied using a similar thermal decomposition mechanism.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, an organic metal thermal decomposition mechanism is provided, the organic metal is decomposed by independently supplying thermal energy, and the metal generated by the decomposition is It is possible to supply atoms to the substrate. Therefore, according to the present invention, the amount of carbon impurities incorporated into the semiconductor thin film can be significantly reduced, and a high quality semiconductor thin film can be grown at a low substrate temperature.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for semiconductor thin film vapor phase epitaxy provided with an organometallic gas thermal decomposition mechanism used as an example of the present invention. FIG. 2 shows the relationship between the temperature of the thermal decomposition mechanism of organometallic gas and the actual impurity concentration contained in the semiconductor thin film. 1... High purity hydrogen gas supply device 2... Organometallic gas bubbler 3... Constant temperature layer 4... ■ Hydrogenation cylinder 5... Flow rate controller 6... Reactor 6a... Organometallic gas pyrolysis mechanism 6b... Hydride pyrolysis mechanism 6c... Pressure gauge 6d... Semiconductor substrate heating mechanism 7... Semiconductor substrate 8... Vacuum exhaust device

Claims (2)

[Claims] (1) In a method of growing a thin film crystal on a compound semiconductor substrate using at least one of the organic metal gases as a raw material in a reaction vessel, equipment for thermally decomposing the organic metal raw material gas is provided, and the organic metal gas is A semiconductor thin film crystal growth method characterized in that gas is decomposed and supplied to the substrate surface in the form of pure metal molecules. (2) A thermal decomposition mechanism is provided in a reactor having an exhaust device and a substrate heating device, and a hydrogen gas supply device is connected to an organometallic bubbler filled with an organic metal via a flow rate controller, and the organometallic bubbler is connected to an organometallic bubbler filled with an organic metal. One of the thermal decomposition mechanisms is connected to the reactor, and the group V hydride supply device is connected to the reactor through a flow controller and a second of the thermal decomposition mechanisms. Semiconductor thin film crystal growth equipment.