JPH0628236B2 - Gas flow controller - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas flow rate control device used in a vapor phase growth method of a compound semiconductor or the like.

[Conventional technology]

In the semiconductor manufacturing process, for example, AlG is formed on a gallium-arsenide (GaAs) substrate to form a compound semiconductor.
As a method for forming the aAs epitaxial layer, a vapor phase growth method in which a volatile compound of a component element such as trimethylaluminum (TMA) is transferred to a substrate by a carrier gas and reacted and grown on the substrate, so-called MOCVD
(Metal Organic Chemical Vapor Deposition) is known.

This MOCVD is suitable for mass production because the composition and the doping amount of impurities can be controlled by controlling the gas flow rate, a relatively simple and inexpensive device is sufficient, and the growth rate is large and the cycle time is short.

By the way, in such MOCVD, as a method of introducing a volatile compound of each component element, for example, TMA, into the reaction chamber in which the substrate is housed, generally, as shown in FIG. 4, TMA (54) was added. Carrier gas is sent to the bubbler (51) from the inflow passage (52) and bubbled to generate a gas having a predetermined concentration, and this gas is discharged to the outflow passage (53).
The method of sending it into the reaction chamber through is adopted. However, for example, AlGaA with different composition ratios
In order to grow the s epitaxial layer, it is necessary to change the flow rate of the carrier gas to change the concentration of TMA sent to the reaction chamber (that is, the flow rate of gas from the bubbler), as shown in FIG. If the flow rate of the mass flow controller (MFC) is simply changed with such a device, as shown by A or B in FIG. 5, it takes a considerable time for the flow rate of TMA to settle to a predetermined set value. For this reason,
When trying to grow layers having different composition ratios as described above, there is a drawback in that the boundaries between the layers become unclear and predetermined characteristics cannot be obtained. In order to make the boundaries between the layers clear and to improve the characteristics, there is a demand for a flow rate control device capable of abruptly changing the flow rate of TMA as shown by C in FIG.

Therefore, for example, as shown in FIG. 6, two bubblers are provided, each of which supplies a carrier gas by a mass flow controller (MFC) and selectively supplies the gas from the two bubblers to the reaction chamber by operating a valve. A device capable of

This device has two bubblers (51a) and (51b), and each bubbler (51a) and (51b) has a carrier gas inflow path (55), (56) and an outflow path (57). (58) is installed. Then, MFCs (52) and (53) for adjusting the flow rate of the carrier gas are arranged in the middle of these inflow paths (55) and (56). In addition, the outflow passages (57) and (58) are each branched into two passages in the middle, and the branched outflow passages have valves (5
9), (60), (61), and (62) are arranged. That is, in the outflow passage of the one bubbler (51a), the valves (59), (60)
TMA gas can be introduced into the reaction furnace or the exhaust port by switching, and the other bubbler (51b) can also be introduced into the reaction furnace or the exhaust port by switching the valves (61) and (62). . Therefore, each MFC (5
2), the TMA bubbled by the carrier gas controlled by (53), the above valves (59), (60), (61), (6)
By operating 2), either one of the flow rates is selectively introduced into the reactor.

In this case, it is possible to increase the flow rate sharply, but two bubblers are required, and the number of valves increases, making it difficult to switch each valve instantaneously.

On the other hand, as shown in FIG. 7, one bubbler (51c) is used,
The amount of carrier gas flowing into this bubbler (51c) is set to 2 M
A method of controlling the flow rate of TMA sent to the reactor by controlling the switching operation of FCs (65), (66) and valves (67), (68), (69), (70) is also conceivable.

However, even when this device is used, there are drawbacks such as an increase in the number of MFCs and valves, which makes the operation complicated.

Also, as shown in FIG.
C (75), (76) and valves (77), (7) arranged in front of and behind them
8), (79), (80) may be used for control, but in this case as well, similar to that shown in FIG. 4, the flow rate as shown by A or B in FIG. There is a wobble.

[Problems to be solved by the invention]

As described above, in the conventional gas flow rate control device, it is difficult to rapidly switch the flow rate of the gas sent to the reaction furnace to the set value, so it is difficult to control the partial pressure of each component gas, and the characteristics of the growth layer are I couldn't control it. There is also a problem that the operation of the device is complicated.

Therefore, the present invention was proposed in order to solve such a conventional problem, in which the set concentration of gas in the reaction furnace can be rapidly changed, that is, the flow rate from the bubbler can be rapidly changed. Moreover, it is an object of the present invention to provide a gas flow rate control device which is easy to operate.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention has a first gas flow path connected to a bubbler and at least one second gas flow path that always flows a constant gas, and the second gas flow path described above. Are connected to the inflow side and the outflow side of the bubbler of the first gas flow path via valves, respectively, and the flow rate of the gas from the bubbler is rapidly changed by switching the valves. It was done like this.

Furthermore, the present invention relates to a first gas flow path connected to a bubbler and at least one second gas flow channel that constantly flows a constant gas.
Gas flow passages, and the second gas flow passages are respectively connected to the inflow side and the outflow side of the bubbler of the first gas flow passage via valves, and by switching the valves, The flow rate of the gas from the bubbler is changed steeply, and a third gas flow channel is provided on the upstream side of the connection portion of the second gas flow channel and the first gas flow channel on the outflow side of the bubbler. It is connected.

[Action]

In this way, the flow rate from the bubbler is set by providing a flow path that always sends a constant flow rate of carrier gas to the bubbler and a flow path that is connected to the upstream side and the downstream side of the bubbler of this flow path via valves. Can be changed sharply.

That is, in FIG. 1, the carrier gas controlled by the MFCs (5) and (6) is supplied from the first gas flow path (3) by closing the valve (7) and opening the valve (8). While bubbling only with gas, by opening the valve (7) and closing the valve (8), the carrier gas of the combined flow rate in the first flow path (3) and the second flow path (4) is used. Bubbling can be performed, so that the gas flow rate from the bubbler (1) can be sharply changed with a small amount of valve operation.

Furthermore, as shown in FIG. 3, the third flow path is connected to the upstream side of the connecting portion between the first flow path (3) and the second flow path (4) on the downstream side of the bubbler (1). The above bubbler (1)
The flow rate from the
The gas from (1) can be fed into the reactor with a carrier gas at a predetermined flow rate.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing the configuration of an example of a gas flow rate control device to which the present invention is applied.

In this gas flow rate controller, a bubbler (1) containing a volatile compound (liquid) (2) of each component element such as trimethylaluminum (TMA), trimethylgallium (TMG) or arsenic chloride (AsCl) is used. MF on the inflow side
The first gas flow path (3), which is set so that a constant flow rate of carrier gas always flows by C (5), is connected,
An outflow passage (9) leading to the reaction furnace is connected to the outflow side of the bubbler (1).

Further, a second gas flow path is set in the first gas flow path (3) connected to the upstream side of the bubbler (1) by the MFC (6) so that a constant flow rate of carrier gas flows. (4) One branch flow passage (4a) is connected via a valve (7), and the other branch flow passage (4b) is connected via a valve (8) to the downstream side of the bubbler (1). It is connected to the middle of the outflow channel (9).

Therefore, when the valve (7) is closed and the valve (8) is opened, only the carrier gas from the first gas passage (3) having the flow rate set by the MFC (5) is stored in the bubbler (1). Will be introduced. And the gas from this bubbler (1) is the above MFC.
The flow rate is controlled by (6), the carrier gas merges with the inflowing carrier gas through the branch flow path (4b) and the valve (8), and is sent to the reaction furnace.

On the other hand, when the valve (7) is opened and the valve (8) is closed at the same time, the flow rate is set in the bubbler (1) by the carrier gas whose flow rate is set by the MFC (5) and the MFC (6). The carrier gas and the carrier gas are introduced together, and the gas bubbled by the combined carrier gas is sent to the reaction furnace.

Therefore, the flow rate of the gas bubbled by the bubbler (1) can be changed by operating the valves (7) and (8). Here, the concentration of volatile compounds contained in the gas flowing out from the bubbler (1) is constant, and if the gas flow rate on the inflow side of the bubbler (1) changes, the gas flow rate on the outflow side also changes, so the bubbler ( The gas flow rate from 1) can be changed instantaneously. Further, since a constant carrier gas is always flowing through the first gas flow path (3) and the second gas flow path (4) by the MFCs (5) and (6), there is a rising time lag. It will never happen.

FIG. 2 shows the state of changes in the flow rate of gas from the bubbler (1) in this apparatus.

Assuming that the carrier gas flow rate of the first gas flow path (3) is D and the carrier gas flow rate of the second gas flow path (4) is E, the valve (7) is closed and the valve (8) is turned on. During the open period F, the gas flow rate from the bubbler (1) is D. Next, when the valve (7) is opened and the valve (8) is closed, the gas flow rate from the bubbler (1) becomes D + E as shown in the period G in FIG. Further, when the valve (7) is closed and the valve (8) is opened again, the gas flow rate from the bubbler (1) instantly becomes D as shown in the period H.

Therefore, the gas flow rate from the bubbler (1) can be rapidly changed only by operating the two valves (7) and (8).
The concentration in the reactor can be changed instantly.

In addition, in this device, in the first gas flow path (3),
A plurality of gas flow paths may be connected by the same connection method as the second gas flow path (4), and by doing so, bubbling gas of various concentrations can be rapidly fed into the reaction furnace. it can.

Also, in this device, instead of the valves (7), (8),
At the branch point of the second gas flow path (4), for example, a cock may be provided so that the branch flow path (4a) or the branch flow path (4b) can be selected.

By the way, the gas obtained by bubbling the liquid in the bubbler is usually carried to a large amount of carrier gas and sent to the reaction furnace. Therefore, another embodiment of the present invention applied to such an apparatus will be described.

Also in this embodiment, the first gas passage (3) and the second gas passage (4) are connected to the valves (7), (8) in the bubbler (1) by the same connection method as in the previous embodiment. Connected through.

The branch flow path (4b) upstream of the connecting portion (20) between the outflow path (9) on the outflow side of the bubbler (1) and the branch flow path (4b) of the second gas flow path (4). ) Is connected to the third gas flow path (10) set to a predetermined flow rate by the MFC (11).

With such a configuration, the valves (7), (8)
The bubbling gas whose flow rate is controlled by the operation of
It is carried into the reaction furnace by being carried by the carrier gas whose flow rate is controlled by the FC (11).

Also in this case, the concentration of the gas introduced into the reaction furnace can be controlled by switching the valve (7) and the valve (8) as in the previous embodiment.

Further, in the outflow passage (9), the flow path (9a) is arranged on the upstream side of the connection part (20), and the midway part of the flow path (9a) and the connection part (20) Between valves (12), (13) respectively
May be provided. With this configuration, when it is not necessary to send the bubbled gas to the reactor, the valve (13) is closed and the valve (12) is opened to discharge this gas to the exhaust port. When feeding the gas, the valve (13) can be opened, and the gas bubbled sharply through the valve (12) can be fed into the reaction furnace.

In this embodiment also, a plurality of gas flow paths may be provided by the same connection method as the second gas flow path (4),
In this case, various concentrations of bubbling gas can be fed into the reactor.

〔The invention's effect〕

As is clear from the above description, in the present invention,
Since the second gas passages are connected to the first gas passages on the upstream side and the downstream side of the bubbler via the valves, respectively, the flow rate of the gas bubbled by the bubbler can be made steep without a time lag. Can be changed.

Further, since the gas flow rate from the bubbler can be switched only by operating the two valves, the operation is simple and the time lag due to the complexity of the operation is prevented.

Further, the gas flow rate control device of the present invention requires only one bubbler and a small number of valves, so that its configuration is extremely simple.

Furthermore, in addition to the above-described configuration, by connecting a third gas flow path upstream of a connecting portion between the first gas flow path and the second gas flow path, the first gas flow The bubbling gas from the bubbler, the flow rate of which is controlled by the passage and the second gas passage, can be carried to the carrier gas in the third gas passage and fed into the reactor. Also in this case, the flow rate of the bubbling gas from the bubbler can be controlled without causing a time lag, and the operation becomes simple.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of a gas flow rate control device according to the present invention, and FIG. 2 is a time chart showing changes in gas flow rate in this flow rate control device. FIG. 3 is a schematic view showing another embodiment of the present invention in which a third gas flow path is provided. FIG. 4 is a schematic diagram showing a conventional flow control device, and FIG.
The figure is a time chart showing changes in the gas flow rate in this flow rate control device. FIG. 6 to FIG. 8 are schematic diagrams each showing a configuration example of a flow rate control device that can be considered in order to sharply change the gas flow rate from the bubbler. 1 ... Bubbler 3 ... First gas flow path 4 ... Second gas flow path 5, 6, 11 ... Mass flow controller 7, 8 ... Valve 10 ... Third gas flow path

Claims (2)

[Claims] 1. A first gas passage connected to a bubbler and at least one second gas passage through which a constant gas flows at all times, each of which has a valve. It is characterized in that it is connected to the inflow side and the outflow side of the bubbler of the first gas flow path through, and the flow rate of the gas from the bubbler is sharply changed by switching the valve. Gas flow controller. 2. A first gas passage connected to a bubbler and at least one second gas passage through which a constant gas flows at all times, and each of the second gas passages has a valve. Is connected to the inflow side and the outflow side of the bubbler of the first gas flow path via the valve, and the flow rate of the gas from the bubbler is rapidly changed by switching the valve. A gas flow rate control device in which a third gas flow path is connected to the upstream side of a connection portion between the gas flow path and the first gas flow path on the outflow side of the bubbler.