JPH0263543A - Liquid vapor raw material supply device - Google Patents

Abstract

PURPOSE:To restrain the fluctuations of pressure and the flow rate just after the start of growing and to improve the quality of crystal surface by controlling the pressure difference between the main flow and the by-pass flow to be very small in comparison with the error of pressure gauge. CONSTITUTION:Vessels 21, 22 storing liquids, a carrier gas supply system supplying carrier gas into the liquid, and mixed gas sending-out parts which send out the mixed gas consisting of the carrier gas and the vapor of the liquid contained in the carrier gas are provided. Moreover, the main flow line 15 and the by-pass line 16 are provided and the former receives the mixed gas sent out of the mixed gas sending-out parts through valves 6, 19 and introduces it to a reaction chamber, and the latter receives the mixed gas sent out of the mixed gas sending-out parts through valves 7, 20 and introduces it to an exhausting system. The pressure difference between the main flow line 15 and the by-pass line 16 is detected by a flow rate meter 14, and either of pressures of the main flow line and the by-pass line is controlled by means 10, 11 so that the pressure difference becomes zero.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a liquid vapor raw material supply device used when growing semiconductor crystals using liquid vapor as a raw material or when synthesizing chemicals. (Prior Art) It has been conventionally practiced to use liquid vapor as a raw material, control the flow rate of the vapor, and send it into a reaction chamber to grow crystals or synthesize chemicals.

In recent years, metal-organic pyrolysis vapor phase epitaxial method (MOVPE method), which uses the vapor of an organometallic compound as a raw material, has been widely used especially in semiconductor crystal growth methods. In this method, it is necessary to strictly control the flow rate of organic metal vapor, and this controllability greatly influences the quality of the crystal.

Here, assuming the reduced pressure MOVPE method, a conventional liquid raw material supply device is shown in FIG. . The mass flow controller is shown as an example of a gas flow rate control mechanism. The carrier gas, which is controlled at a constant flow rate by the mass flow controller 2, passes through the liquid raw material 4, contains a constant vapor pressure of the liquid raw material, enters the main stream 15 via the valve 6, and is sent to the reaction chamber 12 via the needle valve 17. . In order to improve the controllability of the mass flow controller and the stability of the liquid raw material vapor pressure, the carrier gas containing the liquid raw material vapor is discharged to the bypass 16 through the valve 7 before and after crystal growth. In other words, while waiting before crystal growth, valve 6 is closed and valve 7 is open, and when crystal growth starts, valve 7 is opened.
The valve 6 is in the leap state. When stopping crystal growth, valve 6 is closed again and valve 7 is opened. During these series of valve operations, it is important that a constant flow rate of the carrier gas is stably passed through the liquid raw material 4.

The valve operation procedure described above is shown in Figure 3(a).
FIG. 3(b) also shows the operation procedure of the valve when different types of crystal layers are continuously grown.

A sufficient amount of carrier gas whose flow rate is controlled by a mass flow controller 10.11 is added to the carrier gas that has passed through the liquid raw material to the main stream 15 and the bypass 16, and the mixture is sent to the reaction chamber and the exhaust system, respectively.

Here, the pressure control R structure inside the liquid raw material, the main flow, and the bypass will be described. The pressure inside and around the liquid raw material is slightly higher than atmospheric pressure (~
800 Torr). On the other hand, the reaction is carried out in the reaction chamber under reduced pressure of about 70 Torr. These pressure differences are provided by the needle valve 17, and the pressure upstream of the main stream is monitored by the pressure gauge 8.

Since the total flow rate of the carrier gas flowing into the main stream fluctuates due to valve operations before and after growth, the pressure difference generated between the pressure gauge 8 and the set pressure is fed back to the mass flow controller 10 to keep the pressure upstream of the main stream constant. The pressure setting servo am is shown by a dotted line in the figure.

As mentioned above, the main flow 15 and the bypass 16 are always kept at the same pressure in order to keep the flow rate of the carrier gas passing through the liquid raw material and the vapor pressure of the liquid raw material constant during valve operation at the start of growth. Desirably, therefore, the bypass 16 is also servo-controlled by the pressure gauge 9 and the mass flow controller 11, and the bypass 16 is set at the same pressure as the main flow 15.

(Problem to be Solved by the Invention) In the liquid vapor raw material supply device shown in FIG.
The indicated value of 0 actually has an error of 1 to 2 Torr. Due to this pressure error, for example, when the main flow pressure is higher than the bypass pressure, when the carrier gas (commonly called bubbling gas) that has passed through the liquid raw material at the start of growth is switched from the bypass 16 to the main flow 15, Produces transient reflux.

Such backflow of carrier gas is especially caused by the liquid raw material container 21.
．． This caused fatal damage to 22.

If the bypass pressure is higher than the main flow pressure, a similar backflow occurs during growth arrest. Therefore, when supplying liquid vapor raw material to the reaction chamber using conventional equipment, a short delay time ΔT is provided between closing the bypass (main flow) valve and opening the main flow (bypass) valve. 21
．． A pressure of about 3 Torr is built up in 22 to prevent backflow.

Therefore, immediately after the start of growth, the pressure and flow rate continue to fluctuate during the pressure relaxation time as shown in FIG. 4, and the flow rate of the raw material sent to the reaction chamber also fluctuates. In the figure, ΔP indicates the pressure difference between the main flow and the bypass.

The above-mentioned fluctuations in pressure and flow rate also occur when changing the liquid source to grow layers having two or more different compositions as shown in FIG. 3(b).

These pressure and flow rate fluctuations are a serious obstacle to obtaining high quality crystal interfaces.

(Means for Solving the Problems) Means provided by the present invention to solve the above-mentioned problems are as follows:
a container for storing a liquid; a carrier gas supply system for supplying a carrier gas into the liquid; and a gas mixture of the carrier gas that has passed through the liquid and the vapor of the liquid contained in the carrier gas to be guided out of the container. a mixed gas outlet, a main line that receives the mixed gas led out from the mixed gas outlet via a first valve and guides it to the reaction chamber; A liquid vapor raw material supply device comprising: a bypass line that receives the raw material via a valve and leads to an exhaust system, comprising: means for detecting a pressure difference between the main line and the bypass line; and a means for detecting a pressure difference between the main line and the bypass line; and means for controlling the pressure in at least one of the main line and the bypass line in a direction such that Gq becomes zero Gq.

(Function) In the present invention, in order to minimize fluctuations in pressure and flow rate that occur in the main flow due to valve switching, a bridge line is provided that connects the main flow and the bypass, and the direction and flow rate of the carrier gas flowing through the bridge line is The pressure difference between the main flow and the bypass is maintained at zero by monitoring the pressure difference between the main flow and the bypass and feeding the pressure difference back to the mass flow controller of the bypass.

(Example) The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a system diagram showing one embodiment of the present invention.

Between this solid line, the pressure control of the main flow 15 is performed by the pressure gauge 8 and the mass flow controller 10 as in the conventional device shown in FIG.
A bridge line is provided between Rheometer 6 and Rheometer 1 in between.
4 is installed. The pressure of the bypass 16 is determined by the flowmeter 1
Mass flow controller 11 so that the value of 4 is ±O.
control by applying feedback. If the pressure of the bypass 16 is controlled in this way, regardless of whether there is an error in the pressure of the main flow 15 from the set value, the pressure of the main flow 15 will be controlled.
- the pressure difference between the bypasses 16 can be minimized; The structure and operation of other parts of this embodiment are the same as the conventional device shown in FIG.

(Effect of the invention) In the device of the invention, the main flow-bypass pressure difference ΔP
By keeping the error significantly smaller than the pressure gauge error,
The delay time required for closing and opening the valve can be sufficiently shortened. Therefore, by employing the apparatus of the present invention for growing semiconductor crystals, it is possible to reduce the pressure immediately after the start of growth. Fluctuations in LM are suppressed and the quality of the crystal interface can be improved.

In particular, crystal growth using the apparatus of the present invention has a great effect on improving the interface quality of ultra-thin film layers and multiple quantum well structures (MQW).

8.9 is a pressure gauge, 14 is a flow meter, and 21 and 22 are liquid raw material containers, respectively.

Claims (1)

[Claims] A container for storing a liquid, a carrier gas supply system for supplying a carrier gas into the liquid, and a mixture of the carrier gas passed through the liquid and the vapor of the liquid contained in the carrier gas. a mixed gas lead-out part that leads the gas out of the container; a main line that receives the mixed gas led out from the mixed gas lead-out part via a first valve and leads it to the reaction chamber; A liquid vapor raw material supply device comprising a bypass line that receives a mixed gas via a second valve and leads it to an exhaust system, comprising means for detecting a pressure difference between the main line and the bypass line, and a means for detecting a pressure difference between the main line and the bypass line; A liquid vapor raw material supply device comprising means for controlling the pressure of at least one of the main line and the bypass line in a direction in which the pressure difference becomes zero.