JP2646647B2 - Low pressure vapor phase growth equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to pressure adjustment of a source gas supply system in a reduced pressure vapor phase epitaxy apparatus, and relates to the case where the type of reaction gas supplied to a growth chamber is switched
A main flow path for supplying a main carrier gas to the growth chamber and discharging the same from the growth chamber, and a sub-flow path for discharging the sub-carrier gas without passing through the growth chamber for the purpose of avoiding pressure fluctuation in the source gas flow path. And a switching valve group for switching a plurality of types of reactant gases to be sent to the main flow path or the sub flow path, wherein an exhaust system and a pressure adjustment system of the main flow path and an exhaust system and a pressure adjustment of the sub flow path are provided. The system is provided independently.

Further, in another configuration of the present invention, a pressure adjusting gas is supplied to the main flow path and the sub flow path, and by adjusting the flow rate of the pressure adjusting gas, the pressure of the main flow path and the sub flow path is set to a predetermined value. Value is maintained.

[Industrial applications]

It goes without saying that the vapor phase crystal growth apparatus plays an important role in the element formation process in the semiconductor industry.
In recent years, with the development of high-performance devices having a superlattice structure, a crystal growth method capable of growing crystals in atomic layer units has been desired.

In the epitaxial growth of compound semiconductors, MOCVD using an organic metal as a raw material is regarded as an important crystal growth method capable of controlling the thickness of an atomic layer. Crystal growth reduced to Torr is performed.

In addition, not only when a plurality of heterojunctions are stacked like a superlattice but also when a single heterojunction is formed, a semiconductor layer is used in a high-performance device such as a 1 μm band optical device or a high electron mobility transistor. Is required to change steeply across the junction.

In low-pressure vapor phase growth, the composition of the growth layer fluctuates due to fluctuations in pressure conditions. Therefore, in order to form a heterojunction with the designed composition, it is necessary to switch the source gas supplied to the growth apparatus without pressure fluctuation. It is.

In order to meet such demands, a plurality of source gases are constantly flowed in this type of reduced-pressure vapor deposition apparatus, and only a source gas of a semiconductor to be grown at each time is selectively supplied to the growth apparatus. . That is, the source gas of the semiconductor not involved in the growth is flowed through a separately provided vent line, and the valve is switched to be sent to the growth apparatus when needed. The pressure in the vent line is kept the same as the flow path on the growth apparatus side, so that pressure fluctuation does not occur when the source gas is switched.

If the pressures of a plurality of source gases are kept the same and switched between them, the pressure fluctuation in the growth apparatus is suppressed, and the growing semiconductor layer has uniform composition and sharp changes in the composition near the interface. Excellent in terms of properties can be obtained.

[Conventional technology]

The configuration of this kind of conventional vacuum growth apparatus is as shown in FIG. The gas supply system 1 contains various reaction gases, respective carrier gases, a compensation gas which is a dummy at the time of switching, and the like, and is connected to a switching valve 2 which is an integrated valve.

Now, assuming that only two kinds of reaction gases are supplied in a switched manner for easy understanding, the number of kinds of gases contained in the gas supply system is limited to the reaction gases I and II, the main carrier gas, the subcarrier gas, and the compensation gas. There are five types of gas.

The main carrier gas is the main component of the gas flowing in the main flow path 4 connected to the reaction tube 6, and the sub-carrier gas is the main component of the gas in the sub flow path 5 discharged without being connected to the reaction tube. a is, for example, both of H _2. The pressure in the two flow paths is mainly determined by these carrier gases, and a differential pressure gauge 3 for detecting a pressure difference is connected between the pipes of the two carrier gases.

The operation of the switching valve is as follows. When the reaction gas I is supplied to the reaction tube 6, the flow between the pipe for the reaction gas I and the main flow path and the pipe for the reaction gas II and the sub flow path is conducted, and the compensation gas flows into the sub flow path. When switching the source gas, first, the valve is opened and closed so that the flow paths of the reactant gas I and the compensating gas are exchanged, so that the compensating gas flows through the main flow path and the reactant gas I flows through the sub flow path. After all the reaction gas I in the reaction tube has been exhausted, the valve is opened and closed again to flow the reaction gas II through the main flow path and the compensation gas through the sub flow path. During that time, the state in which the reaction gas I flows through the sub flow path is maintained.

In order to maintain the pressure inside the reaction tube at a predetermined reduced pressure value, evacuation by the rotary pump 9 is performed. At this time, the pressure inside the reaction tube is detected by the pressure gauge 7 and the butterfly valve 8 is operated based on the detected value. . Thereby, the pressure in the reaction tube is maintained at a constant value.

On the other hand, in the sub flow path 5, the conductance of the flow path is adjusted by the manual valve 10 so that the indication of the differential pressure gauge 3 becomes zero. As long as there is no pressure difference between the main flow path and the sub flow path, the fluctuation in the pressure in the reaction tube becomes small even when the switching valve 2 is opened and closed, and the composition of the grown crystal does not largely deviate from the design value.

In the growth of the III-V compound, the reaction gas was TM
The carrier gas such as organic metal (MO) such as G and TMI, and AsH ₃ and PH ₃ is often H ₂ . Further, the compensation gas is also usually H _2.

[Problems to be solved by the invention]

In the above-described configuration of the vapor phase epitaxy apparatus, if a compensating gas is used for the switching of the reaction gas, the pressure is inevitably changed due to the difference in density and viscosity, and a good heterojunction is obtained by forming a transition layer. There is no problem. Further, if the exhaust system of the main flow passage and the sub flow passage is made common and the exhaust speed is controlled by only one butterfly valve, there is also a problem that the response speed is slow and it is difficult to follow minute pressure fluctuations.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reduced-pressure vapor deposition apparatus capable of minimizing pressure fluctuation due to source gas switching and realizing a heterojunction without an uncontrollable transition layer.

[Means for solving the problem]

In order to achieve the above object, a reduced-pressure vapor phase growth apparatus of the present invention supplies a main carrier gas to a growth chamber and discharges the main carrier gas from the growth chamber, and a sub-flow path for discharging a subcarrier gas without passing through the growth chamber. A flow path, and a switching valve group for switching a plurality of types of reaction gases to be supplied to a main flow path or a sub flow path; an exhaust system and a pressure adjusting system for the main flow path; an exhaust system for the sub flow path; It is provided separately from the pressure adjustment system.

Further, in another configuration of the present invention, a pressure adjusting gas is supplied to the main flow path and the sub flow path, and by adjusting the flow rate of the pressure adjusting gas, the pressure of the main flow path and the sub flow path is set to a predetermined value. Value is maintained.

[Action]

If the decompression and exhaust devices for the main flow path and the sub flow path and the pressure adjustment system are provided independently, the pressure in the growth chamber can be controlled more precisely. In particular, if the pressure difference between the main flow path and the sub flow path is adjusted by one pressure adjustment system and the pressure of the growth chamber is adjusted by the other pressure adjustment system as in the later-described embodiment, the reaction gas can be switched. Therefore, the fluctuation of the pressure generated due to the above is suppressed twice, and the fluctuation of the composition of the semiconductor layer to be grown can be made extremely small.

Furthermore, as in another configuration of the present invention, if an auxiliary gas for pressure adjustment is introduced into each flow path and pressure adjustment is performed by using the auxiliary gas, it is possible to follow a rapid pressure fluctuation and compensate for it. Is possible, which is more effective in achieving the object of the present invention.

〔Example〕

FIG. 1 is a schematic diagram showing a configuration of an embodiment of the present invention.
Hereinafter, description will be made with reference to the drawings.

The gas supply system 1 and the switching valve 2 are the same as those in the prior art shown in FIG. The differential pressure gauge 3 is a simple monitor in the configuration of FIG. 3, but is a pressure sensor for control in the present invention. This will be described later.

The pressure in the reaction tube 6 is detected by a pressure gauge 7, and the output thereof activates a butterfly valve 8 to maintain the pressure in the reaction tube at a predetermined value. 9 is a rotary pump. This part is also similar to the prior art in FIG. 3, but the conductance of the butterfly valve 8 is adjusted only in the main flow path.

In the present invention, a butterfly valve 8 'and a rotary pump 9' are also provided on the sub-flow path side, and the butterfly valve 8 'is operated by the output of the differential pressure gauge 3 provided between the main carrier gas and the sub-carrier gas. The conductance of the path is adjusted to control and maintain the pressure difference between the main carrier gas and the subcarrier gas at zero.

By adopting such a configuration, it is possible to suppress the pressure fluctuation in the vicinity of the valve accompanying the switching of the reaction gas and to absorb the pressure fluctuation that could not be controlled there by independently controlling the pressure in the reaction tube. become.

FIG. 2 is a schematic diagram showing another configuration of the present invention. Hereinafter, other embodiments of the present invention will be described with reference to FIG. 2. However, those given the same reference numerals as those in FIG. 1 or FIG. 3 are devices having the same functions, and therefore the description will be omitted unless necessary. .

The pressure in the reaction tube 6 during the crystal growth is, for example, 76 Torr. Before the growth starts, a mixture of a main carrier gas and a compensation gas, which is a dummy reaction gas, is passed through the main flow path 4. The rotary pump 9 and the butterfly valve 8 are operated to roughly adjust the pressure. Since the response speed of the butterfly valve is low, the pressure gauge 7 may have a low response speed.

The pressure adjusting gas is H ₂ , the same as the primary and secondary carrier gas,
The gas flows into the exhaust system through the flow meter 12 and the control valve 11 as shown in the figure. This flow rate is about 10% of the main carrier gas. After the pressure in the reaction tube is roughly adjusted by the butterfly valve 8, the pressure in the reaction tube is controlled precisely and at high speed by the operation of the control valve 11 according to the output of the pressure gauge 7 '.

It is desirable that these two pressure adjustment systems have different response speeds so that they do not interfere with each other, but after the coarse adjustment is completed, the butterfly valve is fixed, and thereafter the pressure adjustment is performed. The pressure inside the reaction tube may be maintained at a predetermined value only by controlling the flow rate of the adjustment gas. A control valve having a response speed of about 10 ms is commercially available, and the above configuration can be easily realized.

The distribution system 13 connected in front of the reaction tube is a device for uniformly feeding the raw material gas into the reaction tube.
Since a pressure loss of 50 Torr occurs, the pressure in the main flow path from the switching valve 2 to the distribution system 13 is about 126 Torr. It is impossible with a configuration like the prior art to prevent pressure fluctuation when switching the gas connection in a flow path having a low conductance as described above, and it becomes possible only by the present invention.

On the other hand, the pressure is also precisely adjusted on the side of the sub flow path by using the pressure adjusting gas. That is, the pressure in the piping is detected by the pressure gauge 7 ", the conductance is adjusted by driving the butterfly valve 8 ', and the control valve 11' is operated by the output of the differential pressure gauge 3 to thereby connect the main flow path and the sub flow path. .12 for controlling the pressure differential 0 'is flow meter, pressure control gas is the same as the main channel H _2.

In the above configuration, the total flow rate of both the main and sub flow paths is 10 / m
and the flow rates of the reactant gases I and II and the compensation gas are 1 / m each
As in, a pressure fluctuation of ± 0.05 Torr or less and a response speed of 1 sec when this was switched could be realized.

〔The invention's effect〕

As described above, according to the reduced pressure vapor phase epitaxy apparatus of the present invention, pressure fluctuation during growth is effectively suppressed,
The composition changes sharply when the heterojunction is formed, the composition as designed can be realized, and a semiconductor element with excellent performance can be formed.

[Brief description of the drawings]

 FIG. 1 is a schematic diagram showing a configuration of the present invention, FIG. 2 is a schematic diagram showing another configuration of the present invention, and FIG. 3 is a schematic diagram showing a configuration of a conventional growth apparatus. 1 is a gas supply system, 2 is a switching valve, 3 is a differential pressure gauge, 4 is a main flow path, 5 is a sub flow path, 6 is a reaction tube, 7,7 ', 7 "is a pressure gauge, and 8,8' is a butterfly valve. Reference numerals 9, 9 'are rotary pumps, 10 is a manual valve, 11, 11' is a control valve, 12, 12 'is a flow meter, and 13 is a distribution system.

Claims (2)

(57) [Claims] A main flow path for supplying and discharging a reaction gas and a main carrier gas to and from the growth chamber; and a reaction gas and a subcarrier gas different from the reaction gas without passing through the growth chamber. A reduced pressure gas phase growth apparatus comprising: a sub flow path for discharging; and a switching valve group for exchanging the flow paths of the plurality of reaction gases and supplying different reaction gases to the growth chamber in a time division manner. And an exhaust system and a pressure adjusting system of the main flow path and an exhaust system and a pressure adjusting system of the sub flow path are provided independently of each other. 2. The reduced pressure vapor phase epitaxy apparatus according to claim 1, wherein a pressure adjusting gas is supplied to at least one of the main flow path and the sub flow path, and a pressure in the flow path or a pressure between the flow paths. The depressurization is characterized in that the pressure of the main flow path and the sub flow path is maintained at a predetermined value by adjusting the flow rate of the pressure adjusting gas based on a pressure difference or the pressure of the growth chamber. Vapor growth equipment.