JPH01220821A - Gas controlling method for vapor growth equipment - Google Patents

Abstract

PURPOSE:To stabilize gas flow by controlling each instantaneous total amount of gas flowing through a main line and a bent line so as to be equal, controlling each internal pressure of the main line and the bent line so as to be equal, and controlling the internal pressure of a reactor so as to be constant. CONSTITUTION:A group III gas supplying source 10 is subjected to bubbling with carrier gas for bubbling from an MFC12, and the obtained group III gas is sent out to a group III gas supplying line 15. In the group III gas supplying line, the group III gas is diluted with diluent carrier gas sent from an MFC43. The total amount of gas flowing through the MFC12 and the MFC43 flows into a main line 4 or a bent line 6 via a line 11, by switching change-over valves 17A, 17B. The switching of the change-over valves 17A, 17B and 48A, 48B is so controlled that flow rate compensation carrier gas having the same flow rate with the group III gas flowing into either one of the main line or the bent line flows into the other one of the main line 4 or the bent line 5. Thereby the gas flow is always stabilized, so that an epitaxial substrate having a sharp boundary surface can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gas control method for a vapor phase growth apparatus that performs vapor phase growth on a substrate by a metal organic chemical deposition method (hereinafter referred to as MOCvD method). It is.

[Prior Art] The MOCVD method, in which GSAS crystals are grown on a substrate made of a GaAS wafer, is an effective process for manufacturing high-speed electronic devices and optical devices. The vapor phase growth equipment that performs this process is used for arsine (ASH3) of group V, trimethylgallium Qa (CH3) 3 (hereinafter referred to as TMG) of group II, and trimethylaluminum AA (hereinafter referred to as TMG).
CH3) 3 (hereinafter referred to as TMA) is used, and H2 is used as a carrier gas.In addition, this vapor phase growth apparatus places a susceptor with a substrate mounted inside a reactor, and heats these to 650 to 800 °C. , here ASHs, T
-Flow MG or TMA to cause a thermal reaction and cause crystal growth on the substrate. In this case, the A
SH3 and H2 are constantly flowing, but TMG and TMA are flowing into the reactor as needed (for example, for each thin film layer).

At this time, the piping system that flows into the reactor is called the main line.
The piping system that bypasses the reactor and flows directly to the exhaust side is called a vent line. A flow control valve for controlling the flow rate of gas is connected to the main line and the vent line, respectively. In the MOCVD method, it is important to smoothly switch between the main line and the vent line, and whether or not this can be done smoothly greatly affects the stability and reproducibility of the entire process. Note that the flow rate of the flow control valve fluctuates considerably due to pressure fluctuations, so care must be taken when handling it.

FIG. 2 shows the configuration of a conventional vapor phase growth apparatus. In the figure, 1 is the reactor, 2 is the susceptor inside the reactor 1, 3 is the substrate supported by the susceptor 2, 4 is the main line that flows gas to the reactor 1, and 5 is the main line that bypasses the reactor 1 and goes directly to the exhaust side. Vent lines 6 and 7 through which gas flows are flow control valves (6 and 7) connected to the upstream side of each line 4.
8 is a carrier gas line for supplying a carrier gas consisting of H2 to the MFCs 6 and 7, and 9 is an exhaust line from the reactor 1. 10 is the TM of ■ tribe
A first ■liquid gas supply source that supplies G by vaporizing it by bubbling carrier gas; 11 is a first ■liquid gas supply source 1;
0 is a first bubbling line that supplies carrier gas for bubbling; 12 is a valve provided in the first bubbling line 11; MFC 113 is a valve provided in the first bubbling line 11 on the inlet side of MFCl 2; 1st
The valve 15 is provided in the first bubbling line 11 on the inlet side of the liquid gas supply source 10, and the valve 15 is for directing the first liquid gas from the first liquid gas supply source 11 to the main line 4 or vent line 5. The first liquid gas supply line 16 is a valve provided in the first liquid gas supply line 15.
7A and 17B are switching valves for switching between supplying the first liquid gas supplied from the first liquid gas supply line 15 to the main line 4 or the vent line 5. A second liquid gas supply source that vaporizes and supplies TMA by bubbling carrier gas, 19
20 is the MFC provided in the second bubbling line 19; 21 is the MFC; 20 is the MFC provided in the second bubbling line 19;
20 is a valve provided in the second bubbling line 19 on the inlet side of the liquid gas supply source 18; 22 is a valve provided in the second bubbling line 19 on the inlet side of the liquid gas supply source 18; A second liquid gas supply line that supplies liquid gas from the liquid gas supply source 18 to the main line 4 or vent line 5; 24 is a valve provided in the second liquid gas supply line 23; , 25A, and 25B are switching valves for switching between supplying the second liquid gas supplied from the second liquid gas supply line 23 to the main line 4 or the vent line 5. 26 is AS of V group
27 is a V liquid gas supply line that supplies V liquid gas to the main line 4 or vent line 5; 28 is an M provided in the V liquid gas supply line 27;
FC, 29 is a valve provided in the V liquid gas supply inlet 27 on the inlet side of the MFC 28, and 30A, 30B is a valve for directing the v liquid gas supplied from the V liquid gas supply inn 27 to the main line 4.
This is a switching valve that switches between supplying to the vent line 5 and the vent line 5.

In such a vapor phase growth apparatus @, a carrier gas consisting of H2 gas at a constant flow rate is supplied to the first. The second liquid gas supply source 10°18 is sent to the first liquid gas supply source 10°18 by bubbling. 2. Switch the constant flow rate of liquid gas to the main line 4 or vent line 5 with valves 17A and 18B.
, 25A, and 25B. Similarly, the V liquid gas is supplied at a constant flow rate under the control of the MFC 28 by switching the switching valves 30A and 30B. At this time, M
The carrier gas sent from FCs 6 and 7 allows the first
．． Second (1) The entire liquid gas and V liquid gas are diluted.

[Problems to be Solved by the Invention] In such a gas control method, the main line and the vent line have different total flow rates, and while the reactor 1 is connected to the main line 4, the vent line 5
The internal pressure is different between the main line 4 and the vent line 5 due to the difference in piping resistance due to the fact that the reactor 1 is not connected. When switching to MFCl2, there is a problem that MFCl2 fluctuates. When MFCI 2 fluctuates in this way, G
AAGaA on the GaAs film 32 on the aAs substrate 31
When crystal-growing the a-film 33 x 1-x , problems arise in that the interface where the gas is switched becomes rough and the steepness of the interface deteriorates. In a high electron mobility transistor (HEMT), which is a high-speed electronic device, the steepness of the interface is required to be 20 Å or less, which is extremely difficult to achieve with such gas switching.

The purpose of the present invention is to prevent the internal pressure from fluctuating between the main line and vent line even when switching the switching valve, and to
An object of the present invention is to provide a gas control method for a vapor phase growth apparatus, which can supply gas while stabilizing the flow of gas, and can also stabilize the pressure inside a reactor.

[Means for Solving the Problems] To explain in detail the present invention for achieving the above object, the present invention includes a main line that supplies gas to a reactor;
and a vent line for discharging the gas directly to the exhaust side without supplying the gas to the reactor, and when supplying the gas for vapor phase growth to the main line by controlling a switching valve, a carrier gas is supplied to the vent line, In a gas control method for a vapor phase growth apparatus in which the carrier gas is supplied to the main line when the gas for vapor phase growth is supplied to the vent line, the total flow rate of the gas flowing to the main line and the vent line is The internal pressures of the main line and the vent line are controlled to be the same, and the internal pressure of the reactor is controlled to be constant.

[Function] By controlling the gas in this way, the differential pressure between the main line and the vent line will always be 0, and even if either the vapor phase growth gas or the carrier gas is supplied to the reactor by the switching valve, the reactor will not react. Gas pressure does not fluctuate. As a result, the gas flow is always stable, so an epitaxial substrate with a steep interface can be obtained.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to FIG. Note that parts corresponding to those in FIG. 2 described above are designated by the same reference numerals. In this embodiment, (1) the main line 4 and vent line 5 are used to send liquid gas, and another main line 34 and vent line 35 are used to send (V) liquid gas, and accordingly a switching valve is used. 30A, 30B
are provided on the main line 34 and the vent line 35.

In the figure, MFs 36 and 37 are connected to the upstream sides of the main line 34 and the vent line 35 and control the flow rate of the carrier gas supplied from the carrier gas line 8.
C, 38, 139 are pressure gauges that measure the absolute pressure of each main line 4°34, and 40 is a control signal that detects the differential pressure between the main line 4 and vent line 5 and makes the differential pressure O.
The differential pressure gauge 41 sent to the FC 7 is a differential pressure gauge that detects the differential pressure between the main line 34 and the vent line 35 and sends a control signal such that the differential pressure becomes O to the MFC 37. 42 is the first
A first dilution line 43 is provided in the first dilution line 42 for diluting the liquid gas with a dilution carrier gas. M.F.C.

44 is a valve provided in the first dilution line 42 on the inlet side of the MFC 43, and 45 is the first liquid gas supply inlet 15.
to the first line 4 or 5 to which liquid gas is not supplied.
In contrast, a flow having the same flow rate as the first liquid gas flowing into the first liquid gas supply line 15 is connected to a first flow rate compensation line that sends a compensation carrier gas to compensate for the flow rate. ,
Reference numeral 46 denotes an MFC provided in the first passing compensation line 45. The set flow rate of this MFC46 is MFCI 2 and M
It is determined to be the sum of each set flow rate of the FC43. 47 is the first flow compensation line 4 on the inlet side of the MFC 46
Valve provided at 5, 48A.

Reference numeral 48B is a switching valve that switches between supplying carrier gas for flow rate compensation supplied from the first flow rate compensation line 45 to the main line 4 or to the vent line 5. Switching valve 17A.

17B, 48A, and 48B are controlled so that when the switching valves on one diagonal line are both open, the switching valves on the other diagonal line are both closed.

49 is a second dilution line that dilutes the second group III gas sent from the second group III gas supply in 23 to the main line 4 or vent line 5 with a carrier gas; and 50 is the second dilution line 49. The provided MFC 51 is a valve 5 provided in the second dilution line 49 on the inlet side of the MFC 50.
2 is a second group III gas flowing from the second group III gas supply line 23 to the second group III gas supply line 23 to line 4 or 5 to which the second group III gas is not supplied. A second flow M compensation line 53 is an MFC provided in the second flow rate compensation line 52, which sends a carrier gas for flow rate compensation at the same flow rate as the flow rate to compensate for the flow rate. This MFC53
The setting flow is determined to be the sum of each setting flow (2) of the MFC 20 and the MFC 50. 54 is a valve provided in the second flow compensation line 52 on the inlet side of the MFC 53;
55A and 55B are switching valves that switch between supplying the carrier gas for flow rate compensation supplied from the second flow rate compensation line 52 to the main line 4 or to the vent line 5.

The switching valves 25A, 25B and 55A, 55B are controlled so that when the switching valves on one diagonal line are both open, the switching valves on the other diagonal line are both open.

56 is an exhaust unit connected to the exhaust line 9;
7 is a pressure gauge that measures the absolute pressure inside the reactor 1. The exhaust unit 56 is configured to control exhaust based on a signal from a pressure gauge 57.

Next, a gas control method in such a vapor phase growth apparatus will be explained. bubbling the first Group III gas supply source 10 with a bubbling carrier gas from the MFCI 2;
The obtained first group ■ gas is transferred to the first group ■ gas supply line 1.
Send it out on 5th. In this first group III gas supply line, M
The first group (2) gas is diluted with the dilution carrier gas sent from the FC43. In the first group (1) gas supply source 10, the first group (1) gas has a near saturated vapor pressure, but due to this dilution, the pressure is no longer saturated. The sum of the gas flow rates flowing into MFCIs 2 and 43 is the sum of the gas flow rates flowing into MFCI 2 and 43.
5 and flows into the main line 4 or vent line 5 by switching the switching valves 17A and 17B. This first
The carrier gas for flow rate compensation at the same flow rate as the flow of the first group III gas flowing into either the main line 4 or the vent line 5 from the group III gas supply in 15 is supplied to the MFC 46.
Flows into the other of the main line 4 or the vent line 5 under the control of. In this case, when the first Group III gas is flowing into either the main line 4 or the vent line 5, the switching valve 17A, Switching control between 17B, 48A, and 48B is performed. Therefore, the same flow rate of gas always flows through the main line 4 and vent line 5, and both lines 4 and 5 are controlled by the differential pressure gauge 40 and MFC 7 so that the differential pressure is O, so the switching valve 17A, Even if switching between 17B, 48A, and 48B is performed, no pressure fluctuation occurs. Therefore, no pressure fluctuation occurs even when the first Group 1 gas flows into the reactor 1 from the main line 4 or when the carrier gas for flow rate compensation flows into the reactor 1.

Similarly, on the second group III gas supply source 18 side, the flow rate is the same as the flow rate of the second group III gas flowing from the second group III gas supply in 23 to either the main line 4 or the vent line 5. The carrier gas for flow rate compensation is MFC53.
Flows into the other of the main line 4 or vent line 5 under the control of

On the reactor 1 side, its internal pressure is detected by a pressure gauge 57, and the exhaust unit 56 is controlled so that this internal pressure is constant. As the exhaust unit 56, a vacuum pump whose rotation speed is controlled, a flow rate control valve that flows a balance gas into the exhaust line 9, or the like is used.

When a reaction occurs in the reactor 1, ASH3+Ga (CH3)3->GaAs+3CH4, and since there are 4 molecules on the right side and 2 molecules on the left side, the pressure inside the reactor 1 increases slightly. A compared to the carrier gas flow rate
The flow rates of SH3 and TMG are both small, so it is not a very large value, but in the case of the low pressure MOCVD method, the exhaust unit 5
6 control and MFC7°37 control are delicately required.

In the case of low-pressure MOCVD, there are 50 to 150 rr te inside the reactor 1, and the m group gas is supplied 'fJ! 10. 18+7)
Since the pressure is approximately atmospheric pressure, a pressure difference is created using a throttle valve 58 at the end of the main line 4 and a throttle valve 59 at the ends of the vent lines 5 and 35.

[Effects of the Invention] As explained above, according to the gas control method for a vapor phase growth apparatus according to the present invention, the differential pressure between the main line and the vent line is always O, and the switching valve switches between the vapor phase growth gas and the carrier gas. There is an advantage that the gas pressure in the reactor does not fluctuate no matter which one is supplied to the reactor. As a result, the gas flow is always stabilized, so that an epitaxial substrate with a steep interface can be formed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a vapor phase growth apparatus for carrying out the method of the present invention, FIG. 2 is a schematic diagram of a conventional vapor phase growth apparatus, and FIG.
The figure is a longitudinal cross-sectional view showing an example of an epitaxial substrate. 1...Reactor, 2...Susceptor, 3...Substrate,
4... Main line, 5... Vent line, 6,7
...MFC, 8...Carrier gas line, 9...
Exhaust line, 10... first group ■ gas supply source, 11.
...First bubbling line, 12...MFC, 15
...First group ■ gas supply line, 17A, 17B...
・Switching valve, 18...Second group ■ gas supply source, 1
9...Second bubbling line, 20...MFC1
23... Second group ■ gas supply line, 26... Group V gas supply source, 27... Group V scum supply line, 28.M
FC130A, 30B...Switching valve, 34...
Main line, 35... Bent line, 36.37.
・・MFC, 38, 39・・Pressure gauge, 40.41・・
・Differential pressure gauge, 42...first dilution line, 43...M
FC145...The first flow is the compensation line, 46...M
FC, 48A, 48B...Switching valve, 4...
2nd dilution line, 50...MFC152...2nd
Flow rate compensation line, 53...MFC155A, 55B
...Switching valve, 56...Exhaust unit, 57.
...Pressure gauge.

Claims (1)

[Claims] A main line that supplies gas to the reactor and a vent line that discharges the gas directly to the exhaust side without supplying the gas to the reactor, and when supplying the vapor growth gas to the main line by controlling a switching valve, In a gas control method for a vapor phase growth apparatus in which a carrier gas is supplied to a vent line, and when the vapor phase growth gas is supplied to the vent line, the carrier gas is supplied to the main line, the main line and the vent line are control so that the total flow rate of the gas flowing through the reactor is the same, the internal pressures of the main line and the vent line are the same, and the internal pressure of the reactor is constant. A gas control method for a vapor phase growth apparatus, characterized in that: