JPH0471993B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a vapor phase growth valve that can epitaxially grow a semiconductor layer with good reproducibility and can form a steep compositional change and impurity distribution. be.

[Conventional technology]

Conventionally, switching of source gas in vapor phase growth of compound semiconductors, particularly in pyrolytic vapor phase growth (hereinafter referred to as organometallic vapor phase epitaxy) using organometallic compounds and hydrides as raw materials, has been carried out using, for example, three steps as shown in Fig. 2.
This is generally done using a directional valve. The prior art will be explained below with reference to FIG.

Fig. 2 is a diagram showing a three-way valve for switching the source gas commonly used in organometallic vapor phase epitaxy;
FIG. 4B is a diagram showing the raw material gas discharge state. In the figure, 1 is the raw material gas inlet, 2 is the supply line to the reactor, 3 is the discharge line, 4 is the cylinder for switching the gas flow path, 5 is the raw material gas flow path, and 6 is the raw material gas retention area in the valve. , 7 indicates a driving source.

In the figure, when switching the raw material gas, the cylinder 4 is moved by pneumatic or electromagnetic operation using a drive source 7 such as a pneumatic pressure source or an electromagnet, and the raw material gas flow path 5 is moved from the supply line 2 to the discharge line 3. Alternatively, this can be done by switching from the discharge line 3 to the supply line 2. In this case, the raw material gas flow path changes from the shaded area 5 in FIG. 2A to the shaded area 5 in FIG. 2B.

[Problems to be solved by the invention]

However, in switching the raw material gas using such a three-way valve, the raw material gas retention area 6 shown in FIG. The reproducibility of the layer properties and the steepness of the heterointerface were significantly reduced.

Furthermore, changing the raw material gas changes the gas flow rate in the supply line, resulting in changes in growth conditions and a problem in that the characteristics of the epitaxial layer change.

In addition, a manifold for vapor phase growth is known in which such three-way valves are aggregated and the retention area shown in Figure 2 (b) has an extremely small volume, but in principle, the retention area of the raw material gas is limited to a certain finite value. Furthermore, since there is also a change in the gas flow rate in the supply line, the above problem has not been fundamentally solved.

In order to solve the above-mentioned problems, the present invention eliminates the retention area of raw material gas in the switching valve,
In addition, by creating a structure in which the gas flow rate of the supply line does not change, we have developed a vapor phase growth valve that enables epitaxial growth of high-quality semiconductor layers with good reproducibility, as well as the formation of steep compositional changes and impurity distributions. The purpose is to provide.

[Means for solving problems]

For this purpose, the vapor growth valve of the present invention has the following features in the source gas switching valve used in the vapor growth apparatus:
A gas channel arranged in an annular shape having a raw material gas inlet, a purge gas inlet, a reactor gas supply port, and a gas discharge port; a first gas flow path switching means for switching between a first gas flow path to the supply port and a second gas flow path from the purge gas inlet to the reactor gas supply port; a second gas flow path switching means for switching between a third gas flow path to the exhaust port and a fourth gas flow path from the purge gas inlet to the gas discharge port; The first gas flow path, the second gas flow path and the third gas flow path are opened and closed at the same time, respectively.
and a driving means for driving the second gas flow path switching means.

[Effect]

The vapor phase growth valve of the present invention arranges the gas flow paths in an annular shape, allows the raw material gas and the purge gas to flow in from each gas inlet, and switches the gas flow paths using the gas flow path switching means. When changing the flow path, there is no stagnation area of the raw material gas in the supply line to the reactor inside the valve, and the total gas flow rate in the supply line to the reactor does not change, thereby achieving a sharp switching of the raw material gas. be able to.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a valve for vapor phase growth according to the present invention, in which FIG. 1A shows a raw material gas supply state, and FIG. 1B shows a raw material gas discharge state. In the figure, parts that are the same as those shown in FIG. 1 are designated by the same numbers. Note that 4a and 4b are cylinders, 7a and 7b are drive sources, and 8 is an inlet for a carrier gas for purging.

In the figure, the gas flow paths are arranged in an annular shape, and cylinders 4a and 4b are arranged in each flow path and are configured to be driven by drive sources 7a and 7b, respectively.

First, when supplying raw material gas, drive source 7
a, 7b to move the cylinders 4a, 4b to the first position.
Driven to the position shown in Figure A, the raw material gas flowing in from the raw material gas supply port 1 flows into the reactor through the supply line 2, and at this time, a purge carrier gas of the same flow rate as the raw material gas flows in from the inlet 8. and is discharged through the discharge line 3.

Next, in the case of raw material gas discharge, the driving source 7a,
7b drives the cylinders 4a and 4b to the position shown in FIG. 1B. In this case, the raw material gas that has flowed in from the inlet 1 is discharged through the discharge line 3. At this time, the purge carrier gas having the same flow rate as the raw material gas flows from the inlet 7 and flows into the reactor through the supply line 2.

In this way, by arranging the gas flow path in an annular shape and driving the two cylinders simultaneously, all the raw material gas existing in the valve is purged by the inflow of the purge carrier gas, so the raw material gas retention area in the valve is becomes a structure that will not survive. Further, since the raw material gas and the purge carrier gas are set at the same flow rate, the total gas flow rate flowing into the reactor does not change due to switching of the raw material gas. moreover,
Since the supply line and the discharge line of the switching valve can be made common for each source gas, it is also possible to aggregate them and downsize them.

〔Effect of the invention〕

Undoping is performed using the organometallic vapor phase growth apparatus equipped with the vapor phase growth valve according to the present invention as described above.
When GaAs was grown, an n-type epitaxial layer with a residual carrier concentration of 10 ¹⁴ to ^{10 15} cm ^-3 was obtained with good reproducibility, and even in an undoped GaAs epitaxial layer immediately after doping with P-type impurities. , the residual carrier concentration was n-type with a residual carrier concentration of 10 ¹⁴ to ^{10 15} cm ^-3 , and it was confirmed that a high quality epitaxial layer could be obtained with good reproducibility.

In addition, as a result of epitaxially growing a heterostructure of GaAs and Al _0.5 Ga _0.5 As and measuring the steepness of the composition change, it was found that the transition region of both is 1 to 2 atomic layers (<5
Å), and it was confirmed that a very steep interface was formed.

Note that although the above embodiments have been explained using organometallic vapor phase growth of GaAs and AlGaAs as examples, the present invention
It is not limited to GaAs, AlGaAs, and
It goes without saying that the method is not limited to the shape or pressure of the reactor, and can be applied to all types of single crystal, polycrystal, amorphous, and metal vapor phase growth.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of a valve for vapor phase growth according to the present invention, and FIG. 2 is a diagram showing a three-way valve for switching source gases used in conventional metal organic vapor phase growth. DESCRIPTION OF SYMBOLS 1... Raw material gas inlet, 2... Supply line, 3... Discharge line, 4, 4a, 4b... Cylinder, 5... Raw material gas flow path, 6... Raw material gas retention area, 7, 7a, 7
b...Drive source, 8...Carrier gas inlet for purge.

Claims (1)

[Scope of Claims] 1. In a source gas switching valve used in a vapor phase growth apparatus, a gas flow path arranged in an annular shape having a source gas inlet, a purge gas inlet, a reactor gas supply port, and a gas outlet. and a first gas flow path arranged in the gas flow path from the raw material gas inlet to the reactor gas supply port, and a second gas flow path from the purge gas inlet to the reactor gas supply port. a third gas flow path from the source gas inlet to the gas outlet; and a fourth gas flow path from the purge gas inlet to the gas outlet. a second gas flow path switching means for switching;
Driving means for driving the first and second gas passage switching means so that the first gas passage and the fourth gas passage, and the second gas passage and the third gas passage are opened and closed simultaneously, respectively. Vapor growth valve with. 2. The vapor growth valve according to claim 1, wherein the first and second gas flow path switching means comprises a cylinder. 3. The vapor phase growth valve according to claim 1, wherein the purge carrier gas is allowed to flow in the same flow rate as the raw material gas, so that the total gas flow rate in the supply line to the reactor does not change when changing the gas flow path. . 4. For vapor phase growth according to claim 1, in which the gas flow path switching means and the annular gas flow path are incorporated into a single block, and the gas supply line and the discharge line are common, respectively, and are aggregated. valve.