JPH0883773A - Thin film forming device - Google Patents

Abstract

PURPOSE: To surely prevent the blockage of a gas discharging system or the malfunction of an exhaust pump caused by an easily settable component contained in an exhaust gas discharged from a reaction furnace. CONSTITUTION: In a thin film forming device provided with a reaction furnace 1 incorporated with a means which holds a substrate 6, means which forms a thin film on the substrate 6 by vapor phase epitaxy by introducing a gaseous starting material to the furnace 1, and exhaust pipe 3 for discharging the unreacted gas of the gaseous starting material introduced to the furnace 1 to the outside from the furnace 1, a cold trap device 21 which is generally maintained at <=-60 deg.C is interposed in the middle of the pipe 3 near the furnace 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film forming apparatus used for manufacturing, for example, a heterojunction compound semiconductor.

[0002]

As is well known, a steep hetero interface is desired in a compound semiconductor having a heterojunction. From the above, in the production of a compound semiconductor having a heterojunction, the vapor deposition method, in particular, a part of the raw material or A vapor phase growth method (MOCVD method) using an organometallic compound for the whole tends to be adopted.

By the way, a thin film forming apparatus for carrying out the MOCVD method is usually constructed as shown in FIG. That is, reference numeral 1 in the figure indicates a reaction furnace. An exhaust port 2 is formed on the bottom wall of the reaction furnace 1, and the exhaust port 2 communicates with the atmosphere through an exhaust pipe 3, a rotary pump 4 for exhaust, and an adsorption tower 5.

A susceptor 7 for holding a crystal substrate 6 as a sample is arranged in the lower part of the reaction furnace 1. An electric heater 8 for heating the crystal substrate 6 via the susceptor 7 is arranged on the lower surface side of the susceptor 7.

In this figure, a system for controlling the crystal substrate 6 to a predetermined temperature, a system for supplying a source gas into the reaction furnace 1,
The valves and the like provided in each part are omitted. When the compound semiconductor film, for example, GaAsP, is vapor-phase grown on the crystal substrate 6 by using the thin film forming apparatus configured as described above, the following is performed.

First, after the crystal substrate 6 is placed on the susceptor 7, an inert gas such as nitrogen gas is introduced into the reaction furnace 1 through the inlet 9 and the rotary pump 4 is operated to remove impurities in the reaction furnace 1. Eliminate gas. Next, the supply of nitrogen gas is stopped, and the inside of the reaction furnace 1 is set to a predetermined pressure (for example, 0.
Exhaust up to 1 Torr or less).

Next, arsine (AsH ₃ ) is introduced into the reaction furnace 1 through the inlet 9 together with a carrier gas (for example, hydrogen), the pressure is kept constant (for example, about 10 Torr), the electric heater 8 is energized, and the susceptor 7 is activated. The crystal substrate 6 is heated to a predetermined constant temperature via. After that, phosphine (PH ₃ ) and trimethylgallium (Ga), which are growth gases, are used.
(CH) ₃ ) is introduced into the reaction furnace 1 through the inlet 9 to grow a thin film on the crystal substrate 6.

At this time, the gas that has not contributed to the growth of the thin film reaches the adsorption tower 5 through the exhaust port 2, the exhaust pipe 3, and the rotary pump 4 formed in the bottom wall of the reaction furnace 1, and reaches the adsorbent. Adsorbed. Hydrogen, which is a non-adsorbed carrier gas, is released into the atmosphere.

However, the conventional thin film forming apparatus constructed as described above has the following problems. That is, when phosphine is used as the introduction gas, most of the phosphine is decomposed into phosphorus and hydrogen, and the rest is not decomposed. Part of phosphorus generated by decomposition contributes to film formation, and the rest does not contribute to film formation. The phosphine that was not decomposed, the hydrogen that was generated by the decomposition, and the phosphorus that did not contribute to the film formation were discharged from the exhaust port 2 to the exhaust pipe 3
However, since phosphorus solidifies at several tens of degrees Celsius, this phosphorus is solidified and deposited on the inner surface of the exhaust pipe 3 or the rotary pump 4 as shown by 11 in the figure. Inflow and solidify. When phosphorus is solidified and deposited on the inner surface of the exhaust pipe 3, the flow passage cross-sectional area becomes narrow, which causes the flow passage to be blocked or the pressure in the reaction furnace 1 to rise. Therefore, the predetermined film formation may be difficult. Further, when the flow path is blocked, the pressure inside the reactor 1 rises abnormally,
For example, if the reaction furnace 1 is made of glass, there is a risk of explosion. The same problem occurs when the rotary pump 4 stops due to the solidification of phosphorus.

[0010]

As described above, in the conventional thin film forming apparatus, a phenomenon, such as a component of the decomposition components that does not contribute to film formation, is solidified and deposited in the gas exhaust system, and There was a problem that the normal driving is hindered by.

Therefore, the present invention provides a thin film forming apparatus capable of surely preventing the blockage of the gas exhaust system and the malfunction of the exhaust pump due to the components which are easily solidified among the decomposed components and can always perform the normal operation. Is intended.

[0012]

In order to achieve the above object, the present invention provides a reaction furnace equipped with a means for holding a substrate therein, and a source gas is introduced into the reaction furnace to form a substrate on the substrate. In the thin film forming apparatus provided with a means for vapor phase growing a thin film and a gas discharging means for discharging an unreacted gas of the raw material gas introduced into the reaction furnace to the outside of the reaction furnace, the reaction furnace And -60 ° C between the gas discharge means and
It is characterized in that a cold trap means kept below is provided.

Further, it is characterized in that a constant temperature mechanism for keeping the temperature of the gas passage at about 100 ° C. or more is further provided on the outer periphery of the gas passage located between the reaction furnace and the cold trap means.

[0014]

As described above, in the thin film forming process by the vapor phase epitaxy method, not all the raw material gas is used for the thin film forming reaction. A part of the source gas flows from the reaction furnace to the exhaust system without contributing to film formation. Depending on the type of the raw material gas, a component that can be thermally decomposed and solidified in the reaction furnace is generated. Taking phosphine as an example, it produces phosphorus as a component capable of solidifying. Therefore, a part of phosphorus flows from the reactor to the exhaust system. But,
As in the present invention, there is almost no difference between the reactor and the gas discharging means.
If cold trap means kept at 60 ° C is provided,
All of the gas that can be solidified can be collected by cold trap means. For example, in the case of phosphorus,
By keeping the temperature of the cold trap means at approximately −60 ° C., almost 100% can be collected by this cold trap means. Therefore, it is possible to reliably prevent the blockage of the gas exhaust system and the malfunction of the exhaust pump due to the easily solidified component of the decomposition components, and it is possible to always perform normal operation. Note that phosphorus does not accumulate in the gas passages maintained at 100 ° C or higher.

[0015]

Embodiments will be described below with reference to the drawings. FIG. 1 shows a thin film forming apparatus according to an embodiment of the present invention. In this figure, the same functional parts as those in FIG. 3 are indicated by the same reference numerals. Therefore, detailed description of the overlapping portions will be omitted.

The thin film forming apparatus according to this embodiment is different from the conventional apparatus in that a cold trap device 21 which is maintained at a temperature of -60 ° C. or lower in the exhaust pipe 3, particularly near the reaction furnace 1 is used. A constant temperature mechanism 22 is provided to keep the temperature of the exhaust pipe 3 around the portion 3a located between the cold trap device 21 and the reaction furnace 1 at about 100 ° C. or more.
Has been established.

The cold trap device 21 is composed of a metal container 31, a plurality of metal trap plates 32 mounted on the inner surface of the container 31 in a stepped manner from top to bottom, and a peripheral portion of the top wall of the container 31. And a gas introduction port 33 which is provided in the container 31 and communicates the inside of the container 31 with the portion 3a of the exhaust pipe 3, and one end side of which is inserted into the container 31 so as to commonly pass through each trap plate 32 from above to below, The refrigerant passage 3 is disposed between the gas guide pipe 34 whose end side penetrates the upper wall of the container 31 and is connected to the portion 3b of the exhaust pipe 3 and the container 31 which is arranged around the container 31.
5, and a coolant supply source (not shown) that causes liquid nitrogen as a coolant to flow through the coolant passage 35. The interval between the trap plates 32 is set to be wider toward the upper side.

On the other hand, the constant temperature mechanism 22 is constituted by a heater mechanism provided around the portion 3a of the exhaust pipe 3. A compound semiconductor film such as GaA, which is a compound semiconductor film, is formed on the crystal substrate 6 by using the thin film forming apparatus configured as described above.
In the case of vapor-depositing sP, the procedure is as follows.

First, after placing the crystal substrate 6 on the susceptor 7, an inert gas such as nitrogen gas is introduced into the reaction furnace 1 through the inlet 9 and the rotary pump 4 is operated to remove impurities in the reaction furnace 1. Eliminate gas. Next, the supply of nitrogen gas is stopped, and the inside of the reaction furnace 1 is set to a predetermined pressure (for example, 0.
Exhaust up to 1 Torr or less).

Next, the constant temperature mechanism 22 is operated to operate the exhaust pipe 3
The portion 3a is kept at 100 ° C. or higher, for example, 120 ° C., and liquid nitrogen is passed through the refrigerant passage 35. Each trap plate 32 of the cold trap device 21 is cooled to approximately -60 ° C. by the flow of the liquid nitrogen.

Next, arsine (AsH ₃ ) is introduced into the reaction furnace 1 through the inlet 9 together with a carrier gas (for example, hydrogen), the pressure is kept constant (for example, about 10 Torr), and then the electric heater 8 is energized to make the susceptor 7 operate. The crystal substrate 6 is heated to a predetermined constant temperature via. After that, phosphine (PH ₃ ) and trimethylgallium (Ga), which are growth gases, are used.
(CH) ₃ ) is introduced into the reaction furnace 1 through the inlet 9 to grow a thin film on the crystal substrate 6.

At this time, the gas that did not contribute to the growth of the thin film is the exhaust port 2 and the exhaust pipe 3 formed in the bottom wall of the reactor 1.
Portion 3a, inside the container 31 of the cold trap device 21,
The gas flows through the gas guide pipe 34, the portion 3 b of the exhaust pipe 3 and the rotary pump 4 to the adsorption tower 5.

In this case, among the phosphorus produced by the decomposition of phosphine as the growth gas, the phosphorus that did not contribute to the growth also passes from the exhaust port 2 through the portion 3a of the exhaust pipe 3 into the container 31 of the cold trap device 21. However, since the portion 3a of the exhaust pipe 3 is heated to 100 ° C or higher, it does not solidify and deposit on the inner surface of this portion 3a, and after flowing into the container 31 of the cold trap device 21, the temperature rises to -60 ° C. As shown in FIG. 11, the surface of the cooled trap plate 32 is adhered and collected almost 100%. The arsine and phosphine that have not been decomposed are not solidified by the trap plate 32 because of the difference in the degree of condensation with phosphorus, but are collected by the adsorption tower 5.

As described above, it is possible to prevent phosphorus that has not contributed to growth from solidifying and depositing on the inner surface of the exhaust pipe 3 or entering the rotary pump 4 and solidifying, so that normal operation is always performed. You can do it.

Experiments have shown that the temperature of the trap plate 32 and the phosphorus collection rate have the relationship shown in FIG. As can be seen from this figure, the collection rate is 0% at 100 ° C, and about 98% or more at -60 ° C. And-
The collection rate remains almost unchanged even at temperatures below 60 ° C. Therefore, it can be said that it is most effective to cool the trap plate 32 to approximately −60 ° C. or lower in consideration of the cost for cooling and maintenance.

The present invention is not limited to the embodiment described above. That is, in the above-described embodiment, the cold trap device in which the trap plates 32 are arranged in the shape of a different shelf is used.
Further, as the constant temperature mechanism, a structure in which a heat insulating material is simply wound and mounted may be used.

[0027]

As described above, according to the present invention,
It is possible to reliably prevent the blockage of the gas exhaust system and the malfunction of the exhaust pump due to the easily solidified component contained in the exhaust gas discharged from the reaction furnace, and it is possible to always perform normal operation.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a thin film forming apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between temperature and phosphorus collection rate in a cold trap device.

FIG. 3 is a schematic configuration diagram of a conventional thin film forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor 2 ... Exhaust port 3 ... Exhaust pipe 3a, 3b ... Part 4 ... Rotary pump 5 ... Adsorption tower 6 ... Crystal substrate 7 ... Susceptor 8 ... Electric heater 9 ... Inlet 11 ... Solidified deposit 21 ... Cold trap device 22 ... Constant temperature mechanism 31 ... Container 32 ... Trap plate 33 ... Gas inlet 34 ... Gas guide pipe 35 ... Refrigerant passage 36 ... Refrigerant passage structural material

Claims (2)

[Claims] 1. A reaction furnace having means for holding a substrate therein, means for introducing a source gas into the reaction furnace to vapor-deposit a thin film on the substrate, and to introduce the reaction gas into the reaction furnace. In a thin film forming apparatus having a gas discharge means for discharging an unreacted gas of the source gas to the outside of the reaction furnace, a temperature of approximately -60 ° C between the reaction furnace and the gas discharge means.
A thin film forming apparatus comprising a cold trap means maintained as follows. 2. A constant temperature mechanism for keeping the temperature of the gas passage at about 100 ° C. or more is further provided on the outer periphery of the gas passage located between the reaction furnace and the cold trap means. The thin film forming apparatus according to claim 1.