JPS6390121A - Vapor phase crystal growth system - Google Patents

Abstract

PURPOSE:To carry out the vapor growth uniformly with good reproducibility by a method wherein passage control parts for other fluids are installed in such a way that they are connected to a vessel for a reactive gas and a vessel for a carrier gas and that they compensate the change in the flow rate with a view to suppressing the fluctuation in the pressure inside a reaction furnace due to the changeover of a valve. CONSTITUTION:Passage control parts for other fluids 26 are installed in parallel with a passage control part for a fluid 25. Flowmeters 27, 28 and valves 29-32 are installed at the pipe arrangement which is branched away from a pipe for a carrier gas. The valves 31, 32 are connected to a bypass 24 together with valves 14, 16, 18, 20, 22, and the valves 29, 30 are connected to a reaction furnace 23 through a pipe together with valves 13, 15, 17, 19, 21. In order to keep the flow rate, e.g., at 6400 cc/min over the whole interval area ranging from the point before the start of a growth process to the point after the growth process, the flowmeter 28 is set to 1200 cc/min if the sum of 5000 cc/min for a carrier gas and 200 cc/min for arsine is 5200 cc/min at an interval before the growth process, and the total flow rate for a gas is kept at 6400 cc/min by closing the valve 23 and by opening the valve 31. During this process, each valve is opened in such a way that a source gas and the flowmeter 27 at the passage control part for other fluids are connected to the bypass 24. In this way, it is possible to obtain a uniformly grown film because the fluctuation in the pressure inside a furnace can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement in a vapor phase crystal growth apparatus widely used for forming semiconductor crystal thin films.

(Prior art) In the vapor phase growth method, a raw material gas for the crystal to be grown is introduced into a reactor, a thermal decomposition reaction is caused, and the crystal is deposited on the substrate.
The VD method is known, and one of them, the MOCVD method, utilizes a thermal decomposition reaction of an organometallic compound.

In this MOCVD method, all raw materials are supplied in a gaseous state, making it easy to control the crystal composition. etc. are being mass-produced.

The outline of the vapor phase crystal growth apparatus normally used to produce GaAs/GaAQAs by this MOCVD method is shown in the second section.
To explain with the diagram, arsine 50, trimethyl gallium (hereinafter abbreviated as TMG) 51. Hydrogen selenide 52 for n-type doping, diethylzinc (hereinafter abbreviated as DEZ) 53 and trimethylaluminum (hereinafter abbreviated as TMA) 54 for p-type doping are prepared as raw materials, and hydrogen is used as a carrier gas 55. .

Among these raw materials, TMG51. DEG53, as well as TM
A54 is liquid at room temperature, so these.

Care is taken to ensure the required amount of gas by bubbling the carrier gas. These raw material gases are introduced into a reactor 56 using hydrogen as a carrier gas, and pyrolyzed gas is deposited on a substrate (not shown) to grow a predetermined crystal. The flow rate of the gas is controlled by a flowmeter 57. .58.59.60
．． According to 61.62, whether these raw material gases are introduced into the reactor 56 or discharged to the exhaust gas line (hereinafter referred to as bypass) 63 is determined by the valves 64-65.6.
7, 68-69.70-71.72-73 by manual or automated equipment.

As mentioned above, it goes without saying that the flow paths for each raw material gas are connected to the bypass 63, and the areas surrounded by dotted lines in the figure, that is, each raw material, flowmeter reactor, and valve, are important in this vapor phase crystal growth apparatus. 2N will be used in the future in the fluid passage control section 74.
shall be.

(Problems to be Solved by the Invention) This vapor phase crystal growth apparatus is used to grow n-type GaAs substrates.
Type AQ, , 4As (n=3 x 1017cn-3)
/Undoped GaAs/P type A20,4Ga0. ,
To form a double heterostructure of As (p=2X1017cm-3), hydrogen dilution 10% arsine, hydrogen dilution 1ppm f12Se, 0°C: TMG, 20'C:
Using TMA, 0” CDEZ, carrier gas hydrogen 50
000 cc/min, arsine 200 cc/m1n constant, V/III ratio, and the total molar flow rate of group Ⅰ also have a growth rate of 0.
It is fixed at 1 μs/akin.

Under these conditions, the total flow rate of gas introduced into the reactor during growth of each layer was 6400cc/1Iin, 5260cc.
c/min and 5320 cc/l1in, and during the interval adopted for gas flow adjustment in each calendar month, a total of 5200 cc/min of arsine and carrier gas flowing to prevent As evaporation was introduced into the reactor. do. In either case, the pressure within the reactor fluctuates from several torr to several tens of torr before and after switching the valves 64 to 73.

One way to suppress this pressure fluctuation is to adjust the flow rate of the carrier gas prior to the growth of each layer to keep the total flow rate of the gas introduced into the reactor constant, but there is a limit to the response of the flow meter. Currently, it is not possible to completely prevent pressure fluctuations.

As a result, the crystallinity 1 composition and carrier concentration distribution at each layer interface are greatly affected.
This becomes the basis for causing abnormalities in T characteristics and deterioration of reproducibility.

The present invention provides a novel vapor phase crystal growth apparatus that eliminates the above-mentioned difficulties, and in particular suppresses pressure fluctuations caused by changes in the total flow rate of gas introduced into the reactor before and after switching the valve,
The purpose is to obtain a crystal growth layer with good reproducibility.

[Structure of the invention]

(Means for Solving the Problems) In the present invention, when introducing multiple types of gases and carrier gas for reaction into a reactor, the flow rate is provided with a mechanism that adjusts according to the flow rate of the gases, such as a mass flow controller. The fluid passage control section is configured by a fluid passage control section consisting of a gas meter and a valve whose role is to control the inflow and outflow of gas. Adopt a method of installing the parts in parallel. In addition, this reactor is communicated with the exhaust pipe.6 (Function) As described above, in the vapor phase crystal growth apparatus according to the present invention, the total flow rate of gas introduced into the reactor can be kept constant even before and after switching the valve. Therefore, it is possible to keep the pressure in the reactor constant at intervals when a plurality of grown crystals are formed in the reactor, and also during all of the crystal growth.

(Example) To explain the present invention in detail with reference to FIG. 1, a hydrogen container 1゜2.3, 4,
5 and 6 were prepared, and as reaction gases, hydrogen diluted 10% arsine was placed in container 1, hydrogen diluted IPPmH,Se was placed in container 2, 0°C TMG was placed in container 3, 20°C TMA was placed in container 4, and 0°C TMG was placed in container 4.
The container 5 is filled with DEZ and the container 6 is filled with hydrogen. Flowmeters such as MFC (mass float controller) 7.8.9.10.
11.12 are provided to adjust the flow rates of reaction gas and carrier gas, and air-driven valves 13-14.15-16.17-18.19-20.
21-22 is similar to the conventional technique. Of course, piping is connected between the valves 13 to 22 and the flow meters 7 to 12, and one of the valves is connected to the reactor 23 by piping.
Furthermore, the other side of the valve is connected to a pipe to a pressure reduction mechanism (not shown) that communicates with the reactor 23. The piping to this pressure reduction mechanism will be referred to as a bypass 24 from now on, and the carrier gas flowmeter 12 will be connected directly to the reactor 23 via the piping, and the flowmeter 7
12, valves 13 to 22, and bypass 24, the area surrounded by dotted lines is defined as fluid passage control section 25.

Furthermore, since TMG, TMA, and DEZ are liquids as described above, carrier gas hydrogen gas is introduced and bubbled to ensure the necessary gas flow rate as described above.

By the way, another fluid passage control section 26 is installed in parallel with this fluid passage control section 25. This is a flowmeter 27.28 and a valve 29.30 on a pipe branched from the carrier gas pipe.
．． 31.32 is provided, and the valve 31.32 is 14.16.1g.
.

Connected to bypass 24 with 20, 22 and valve 29.30
is piped to the reactor 23 along with 13°15, 17, 19, and 21.

Using such a vapor phase crystal growth apparatus, the carrier gas is 5000cc/win, arsine 200cc/wi
n-AQ on an n-GaAs substrate (not shown) installed in the reactor 23 under conditions of a growth rate of 0.14/win.
,,,Ga,,,As (n=3XIO”an-3)/
Undoped GaAs substrate-AI2Ga0. GAs (
A double heterostructure of P=2×10”am-3) is formed.When growing this first layer of n-Al2GaAs, the total flow rate of gas introduced into the reactor is 6400cc/w.
In, the flow rate is set to 6400c over the entire range from the interval before the start of growth to the interval after the end of growth.
Must be held at c/+in.

For this purpose, first, during the interval before growth, the reactor 23
The total flow rate of gas introduced into the carrier gas is 500cc/
Arsine gas 200cc/ to suppress evaporation of win and As
Since the sum of wins is 5200cc/win, the flowmeter 28 of the other fluid passage control section is set to 1200cc/win (6
400cc/m1n-5200cc/ff1in), close the valve 32, open the valve 31, and introduce the gas into the reactor 23, the total flow rate of the gas becomes 6400cc/lll1n.

At this time, the flowmeters 29 of the TMG, TMA, DEZ, and other fluid passage control units are all operated to connect to the bypass 24.

In forming the n-Al1GaAs layer, TMS3, T
Growth starts by opening valves 15, 17, and 19 for MA4, H, and Se2 and closing valves 16, 18, and 20, but valves 31, 29, and 32, provided in other fluid passage control units 26 are closed. Open the reactor 2 and connect it to the bypass 24.
The amount of fluid introduced in Step 3 is maintained at 6400cc/win.

The interval at the end of crystal growth of this n-AQGaAs layer is TM01. TMA4 and 2H, 5Q (7) valve 1
By switching the valves 17 and 19 to the bypass 24 and connecting the valve 31 of the other fluid passage control section 26 to the bypass 24, the total fluid flow rate to the reactor is maintained at 6400 cc/min.

Thereafter, the undoped GaAs layer and P
-IGa-As layer is grown, details of which are shown in Table 1.

(Leaving space below) Table 1 Flow rate setting value and valve opening/closing status at each step The values shown in parentheses in this table are determined by switching the valve.
23) but directly to the bypass 24.

In the vapor phase crystal growth apparatus according to the present invention, the linear flow rate of gas introduced into the reactor can be maintained constant from the start to the end. In addition, when growing a single layer, it is clear from Table 1 that it is sufficient to install other fluid passage control parts alone, and the thickness of the crystal growth layer such as the hole cavity sample This method is effective for applications that require crystal uniformity in the direction, especially near the interface.

Further, three or more fluid passage control units may be connected in parallel, and the present invention can also be applied to compound semiconductors other than those of the embodiments and vapor phase growth of SL.

〔Effect of the invention〕

In this way, pressure fluctuations in the reactor can be suppressed by switching the valves of the vapor phase crystal growth apparatus according to the present invention, so a thin film with high uniformity and reproducibility can be obtained without abnormalities at the interface of the vapor phase growth layer. The effect on mass production is significant.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 is a schematic diagram showing a conventional device.

Claims (1)

[Claims] A reaction gas stored in a plurality of containers, a carrier gas stored in another container, a reactor, an exhaust pipe communicating therewith, and each of the reaction gas and carrier gas introduced into the reactor. A vapor phase crystal growth apparatus characterized by comprising: a fluid passage control section for controlling the reaction gas; and another fluid passage control section connected to the reaction gas container in parallel with the fluid passage control section for compensating for changes in flow rate. .