JPH0397692A - Gasifying and supplying device for organic metallic compound - Google Patents

Abstract

PURPOSE:To lower dispersion of composition by arranging the route of a gaseous raw material which reaches a crystal growing furnace from a vessel with organic metallic compd. filled thereinto, a mass flow controller for carrier gas and a heat exchanger into a thermostatic chamber. CONSTITUTION:A base plate 13 is fitted to a crystal growing furnace 11 and heated at the prescribed temp. and also the inside of a system is evacuated. Then an air thermostatic chamber 24 is raised at fixed temp. to gasify organic metallic compd. 26. The gasified organic metallic compd. is allowed to flow to a mass flow controller 22 by opening a main valve 21 and supplied to the furnace 11 via a raw material supplying valve 23 and a connecting part 32 after regulating the flow rate. On the other hand, carrier gas such as gaseous H2 is regulated to constant flow rate via a valve 30 and a mass flow controller 28 and heated by a heat exchanger 29. The carrier gas of several hundreds times of the gaseous raw material is continuously supplied from the connecting part. The organic metallic compd. 26 is always supplied at uniform concn. into the furnace 11. The epitaxial thin film of a compd. semiconductor is formed on the base plate 13 in the furnace 11.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an apparatus for vaporizing and supplying an organometallic compound used as a raw material when producing an epitaxial thin film of a compound semiconductor by an organometallic chemical vapor deposition method (S!OCVD method).

[Conventional technology]

In recent years, the MOCVD method using organometallic compounds has attracted attention as a crystal growth method for compound semiconductors, and has been actively researched. The MOCVD method is, for example, (Cl31.Ga,
This method uses an organometallic compound such as (CH3)3AL as a raw material and uses its thermal decomposition reaction to grow crystals of a thin film. This method can uniformly form a thin film over a large area, and is excellent in controllability of film thickness and composition ratio, as well as in mass production. In the MOCVD method, for example, when growing a III-V compound semiconductor thin film, (C
Using organometallic compounds such as Hs)sGa and (CHs)sln, AsHa and PH. A hydride such as the following is used. As a method of supplying an organometallic compound into a crystal growth furnace, a carrier gas such as H2 is introduced into the organometallic compound and brought into contact with it through bubbling, and the saturated vapor of the organometallic compound at a predetermined temperature is used for crystal growth. It is installed inside the furnace. FIG. 4 shows a conventional vaporization supply device using this type of carrier gas. In the figure, l is a carrier gas (for example, H2) container, 2 is a pressure reducing valve, 3 is a mass flow controller that controls the mass flow rate of the carrier gas, 4 is an organometallic compound, and 5 is a syringe container filled with an organometallic compound 4. There is. 6 is a constant temperature bath, 7 is an artificial valve, and 8 is an introduction pipe (dip tube), through which carrier gas is introduced into the lower part of the cylinder container 3. 9 is an outlet valve, and 10 is a 21 dollar valve, which reduces the pressure of the gas near the inlet and outlet of the cylinder container 5 by 1 when crystal growth is performed under reduced pressure.
Maintain near atmospheric pressure. 1l is a crystal growth furnace for growing crystals, 12 is a heater, 13 is a substrate, 14 is a vacuum bomb. 15
is a valve for adjusting the degree of pressure reduction. This device is used as follows. First, the vapor pressure of the organometallic compound 4 is determined by accurately controlling the temperature of the constant temperature bath 6. Next, the carrier gas precisely controlled by the mass flow controller 3 is introduced into the cylinder container 4 by opening the valve 7.
Valve 9 is opened and a carrier gas containing an organometallic compound at a desired concentration is introduced into crystal growth furnace II. Crystal growth furnace 1
1 is depressurized by a vacuum bomb 14, and a group V hydride has been previously introduced into the interior through an introduction pipe 16, so that an epitaxial thin film of a compound semiconductor is formed on the substrate 13.

[Problem to be solved by the invention]

When the above-mentioned apparatus is used to perform epitaxial growth of a compound semiconductor, there are problems in that the composition ratio of the obtained epitaxial film deviates from a set value and the electrical properties of the film become non-uniform. In this case, the characteristics of semiconductors obtained from the crystal will vary. The following reasons can be considered for these problems. ■Highly accurate flow rate because the supply amount of the organometallic compound, which is an evitaxial raw material, is controlled by a quadratic function of carrier gas flow rate and temperature! IH wholesale is difficult. ■Since there is no means to directly measure and control the flow rate of the organometallic compound being supplied, it is not possible to detect and control fluctuations in the supply amount. ■There are often many vapor pressure curve diagrams for the same substance for organometallic compounds, which are important guidelines for setting the supply amount, and it is difficult to know which one is the correct one, and it is difficult to determine which one is the most accurate. It is not possible to accurately determine the temperature required to obtain the amount. Furthermore, in order to obtain the desired film thickness and composition, it is necessary to quickly supply and stop the gas. However, this apparatus cannot perform these processes quickly, and the sharpness of the crystal interface cannot be obtained. Even if the gas can be supplied or stopped quickly, the vapor of the organometallic compound and the carrier gas containing it may remain inside the pipe, and the crystals on the substrate 13 may be affected by them. This is particularly likely to be affected when the amount of organometallic compound gas supplied is minute. Furthermore, when the temperature of the carrier gas is low, the temperature of the mixed gas in this device decreases, causing the problem that the organometallic compound condenses in the piping and is not transported properly. The present invention has been made in order to solve the above-mentioned problems, and therefore, it is an object of the present invention to provide an apparatus for vaporizing and supplying an organometallic compound that can quantitatively supply the organometallic compound gas even when the flow rate of the organometallic compound gas is extremely small.

[Means to solve the problem]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus for vaporizing and supplying organometallic compounds according to the present invention for solving the above problems will be described with reference to drawings corresponding to embodiments thereof. The organometallic compound vaporization supply device according to the first aspect of the present invention includes:
As shown in FIG. 1, a container 20 filled with an organometallic compound 26 is connected via a main valve 21 to a mass flow controller 22 for raw material gas, and from the mass flow controller 22 for raw material gas via a raw material gas supply valve 23, it is heated under reduced pressure. The organometallic compound gas path connected to the crystal growth furnace 11 and the carrier gas connected from the carrier gas source to the discharge side connection 32 of the raw material gas supply valve 23 via the carrier gas mass flow controller 28 and heat exchanger 29 A container 20, a path for organometallic compound gas from the container 20 to the crystal growth furnace 11, a carrier gas mass flow controller 28, and a heat exchanger 2.
9 are placed inside a single constant temperature bath 24. The organometallic compound vaporization supply device of the second invention includes a raw material gas supply valve 23 located on the discharge side of the raw material gas mass flow controller 22 of the first invention, and a carrier gas valve 3l located on the discharge side of the heat exchanger 29. is an integrated block valve 35, and the block valve 35 is directly connected to the discharge side of the raw material gas mass flow controller 22 (see FIG. 2). In the organometallic compound vaporization supply apparatus of the third invention, as shown in FIG. 3, a heating means 37 is attached to the heat exchanger 29 of the first invention and the second invention.

【Example】

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an apparatus for vaporizing and supplying organometallic compounds to which the present invention is applied. As shown in the figure, a cylinder container 20 containing an organometallic compound 26 is connected to a pneumatically operated valve 21.
It is connected to the mass flow controller 22 via. The mass flow controller 22 is connected to the crystal growth furnace 1l via an air-operated source gas supply valve 23. A vacuum bomb 14 is connected to the crystal growth furnace 11 via a pressure reduction degree adjusting valve l5. Crystal growth furnace 1. 1 has a structure that is heated by a heater 12, and is provided with an introduction pipe 16 for introducing V group gas or the like. A carrier gas for promoting thermal decomposition, such as hydrogen gas, is supplied through a valve 30, a carrier gas mass flow controller 28,
It is connected at the connection part 32 on the discharge side of the valve 23 via the heat exchanger 29 and the carrier gas valve 3l in this order. Each of the above connections is made by a conduit, forming a closed system. 5 mass flow controllers 2 including cylinder container 20
2, 28, heat exchanger 29, valve 21, 23, 30, 3
1 and the connecting portion 32 are housed in an air constant temperature bath 24. The mass flow controller 22 is one that detects a minute flow rate and has a fast response speed of a flow rate adjustment valve, and is operated at as low a differential pressure as possible. This device operates as follows. First, the substrate 13 is installed in the crystal growth furnace l1, and the heater l2 is turned on.
The system is heated to a predetermined temperature and the pressure inside the system is reduced using a vacuum bomb 14. The valves 30 and 3l are opened to allow a predetermined amount of carrier gas to flow, and the pressure reduction degree adjusting valve 15 is adjusted to keep the pressure reduction degree in the crystal growth furnace 1 constant. The flow rate of the carrier gas should be as large as possible in order to minimize the residence time of the organometallic compound gas in the piping, and is generally about 10 to 300 mg/min. When the air constant temperature bath 24 is heated to a constant temperature, the cylinder container 2
The vapor pressure of the organometallic compound 26 in 0 rises and begins to vaporize. The set temperature of the constant temperature bath 24 cannot be determined uniquely depending on the heat resistance of the mass flow controllers 22 and 28 and valves, the vapor pressure characteristics and thermal decomposition characteristics of the organometallic compound, etc., but the vapor pressure should be made as high as possible. The temperature is set at 50 to 80°C, which is a temperature that can constantly supply sufficient heat of vaporization to the organometallic compound. Here, an air-operated main valve 2 is operated from an operation source (not shown).
1 and the raw material supply valve 23 to open them. Then, the gasified organometallic compound 26 is introduced into the mass flow controller 22 through the valve 2l, and after the mass flow rate is directly measured and adjusted to a constant value, it is supplied into the crystal growth furnace 11 through the valve 23. On the other hand, carrier gas, which is quantified by the carrier gas mass flow controller 28 and sufficiently heated by the heat exchanger 29, is constantly supplied from the carrier gas valve 31. Since the amount thereof is several hundred times as large as the gas amount of the organometallic compound 26, the organometallic compound 26 is supplied to the crystal growth furnace 1l at a constant concentration without any delay time. The carrier gas is heated extremely efficiently because the gas path including the carrier gas mass flow controller 28 is accommodated in the air constant temperature chamber 24. In this way, an epitaxial thin film of a compound semiconductor is formed on the substrate l3 in the crystal growth furnace l. When a predetermined film thickness is obtained, air is supplied to the air-operated supply stop valve 23 and the valve is closed, thereby stopping the supply of the organometallic compound gas. When the flow rate of the organometallic compound 26 is extremely small, the amount of the organometallic compound gas is small compared to the volume of the pipe from the mass flow controller 22 to the connection part 32 via the valve 23, so the gas diffuses unevenly within the pipe. Then, crystal growth furnace 1
The amount supplied to 1 becomes more likely to fluctuate. In that case, the second
As shown in the figure, a block valve 40 in which the valves 23 and 31 are integrated may be used, and it may be directly connected to the outlet side of the mass flow controller 22. The volume of the piping is reduced, the passage time is shortened, and the supply amount is stabilized. The heat exchanger 29 uses the air in the thermostatic chamber 24 as a heat source, and can provide a sufficient amount of heat to the carrier gas.
In the case of heating to a higher temperature, an electric heater 37 or the like may be provided as shown in FIG. 3, and heating may be performed individually. The valves used in the apparatus of the present invention are air-operated or manual valves that are heat resistant and high vacuum resistant. The cylinder container 20 and the piping are preferably made entirely of stainless steel from the viewpoint of safely storing and transporting the organometallic compound. It is desirable that the gas-contact surfaces be subjected to electrolytic polishing treatment.

[Action and effect of the invention]

As described above in detail, the organometallic compound vaporization supply apparatus of the present invention is miniaturized because the organometallic compound gas route including the mass flow controller and the carrier gas route are accommodated in a single constant-water tank. Since the volume of the piping is small and the retention of organometallic compound gas and carrier gas containing it is small, raw materials can be quickly supplied and stopped, and the resulting crystal interface is highly steep. Furthermore, the temperature of the gas can be easily controlled, and there is no condensation of raw materials in the piping. Therefore, regardless of the amount of organometallic compound supplied, it is possible to always control the amount of vapor of the organometallic compound, and it is possible to manufacture thin films of semiconductor crystals with extremely small compositional variations, from thin films to ultra-thin films. As a result, it becomes possible to significantly reduce the cost of devices obtained from the grown crystal.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of an organometallic compound vaporization supply apparatus to which the present invention is applied. FIGS. 2 and 3 each show an embodiment of an organometallic compound vaporization supply apparatus to which the present invention is applied. FIG. 4 is a schematic diagram showing the main parts of a conventional vaporization supply device. 1... Carrier gas container 2... Pressure reducing valve 3.22.
28... Mass flow controller 4, 26... Organometallic compound 5, 20... Cylinder container 6... Constant temperature chamber 7, 9.
2l/23/30/3l...Valve 8...Introduction pipe
lO...21 dollar valve 11...Crystal growth furnace l2...Heater 13...Substrate
l4...Vacuum bomb l5...Valve for adjusting the degree of reduced pressure

Claims (1)

[Scope of Claims] 1. A container filled with an organometallic compound is connected via a main valve to a mass flow controller for raw material gas, and from the mass flow controller for raw material gas is passed through a raw material gas supply valve to a crystal growth furnace under heating and reduced pressure. a carrier gas route connected from a carrier gas source to the discharge side of the raw material gas supply valve via a carrier gas mass flow controller and a heat exchanger; 1. A vaporization supply device for an organometallic compound, characterized in that a path for an organometallic compound gas from a to a crystal growth furnace, a carrier gas mass flow controller, and a heat exchanger are arranged in a thermostatic chamber. 2. A block valve in which a raw material gas supply valve located on the discharge side of the mass flow controller for raw material gas according to claim 1 and a carrier gas valve located on the discharge side of the heat exchanger are integrated, and the block 1. A vaporization supply device for an organometallic compound, characterized in that a valve is directly connected to the discharge side of the mass flow controller for raw material gas. 3. An apparatus for vaporizing and supplying organometallic compounds, characterized in that the heat exchanger according to claim 1 or 2 is provided with heating means.