JPH03201426A - Vapor phase molecular beam epitaxy device - Google Patents

Abstract

PURPOSE:To manufacture the title epitaxy device capable of avoiding the overshoot in case of starting the thin film deposition process as well as cutting down the times of the thin film deposition, discharging material and baking process by a method wherein a suction pump different from that provided on a deposition chamber exhaust gas line is provided in the down stream of a cold trap of a material exhaust gas line. CONSTITUTION:A suction pump comprising a mechanical booster pump 65 and a rotary pump 66 is provided in the down stream of a cold trap 52 in a material exhaust gas line (bypass line) (a). The reason why said two pumps are used is that since the deposition pressure in a deposition chamber 3 is differentiated by the kinds of formed thin films, the pressure in the material gas feed line (b) can be controlled at specific value using said two pumps in proper combination. Through these procedures, the other suction pump can be newly added to a material exhaust gas line so that the material gas feed line may keep the gas flow rate in respective pipings constant even during the material gas exhaust process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas phase molecular beam epitaxy apparatus, and more specifically, a cold trap downstream of a bypass line, which is a raw material exhaust gas line leading from a raw material supply gas line to the outside of the system, The present invention relates to a vapor phase epitaxy apparatus having a suction pump provided in a growth chamber exhaust gas line and a separate suction pump.

[Background Art] In recent years, major changes have occurred in the production of inorganic thin films, particularly thin film materials centered on semiconductor materials. Conventional thin film manufacturing methods include vacuum evaporation, sputtering, C
The VD method is well known, but in recent years metal organic chemical vapor deposition (MOCVD), which uses an organic metal as a gas source and performs the reaction under normal pressure or reduced pressure, and the metal organic chemical vapor deposition (MOCVD) method, which uses a solid material as a raw material and performs the reaction under ultra-vacuum, have been developed. A molecular beam epitaxy (MBE) method has been proposed.

Among these methods, in the MOCVD method, the reaction is carried out under normal pressure or reduced pressure, but because the pressure in the growth chamber is relatively high, the crystal structure cannot be observed in situ, and the thickness of the thin film cannot be controlled. Another problem is that the growth chamber needs to be cleaned after forming a thin film about twice.

In addition, since the MBE method uses solid materials as raw materials, it may take several days to restart after refilling the raw materials, and the resulting Ga
There are problems that oval defects occur in thin films such as As and that growth with good reproducibility is difficult. In addition, when epitaxial growth of GaAs is performed by covering a part of the GaAs substrate surface with an insulator such as 3102, polycrystals grow on the insulator to which crystals should not adhere, so selective epitaxial growth is preferable. There is also the issue of not being able to do so.

In order to solve these problems of the MOCVD method and the MBE method, a vapor phase molecular beam epitaxy (hereinafter referred to as vapor phase MBE) method in which part or all of the raw material is used as a gas source has been proposed. In addition, in recent years, the MBE (MOMBE) method, which uses organometallic compounds such as triethylgallium and triethylaluminum as a gas source, has been developed to produce good crystalline thin films without generating deep impurity levels or oval defects. Development is progressing based on the results obtained.

An example of this MOMBE device is shown in FIG. In the same figure, high purity hydrogen carrier gas is supplied to flow controllers 11 and 12.
After the flow rate is controlled at , the raw material is introduced into the raw material supply chamber 21.22. The raw material supply chamber 21 contains a liquid solution of triethylaluminum, which is a Group Ⅰ raw material, and since this triethylaluminum is a liquid, it is carried by hydrogen gas and supplied to the growth chamber 3 via the flow rate controller 14. Ru. Similarly, the raw material supply chamber 22 contains a liquid solution of triethyl gallium, which is a Group 1 raw material, and is carried by hydrogen gas and supplied to the growth chamber 3 via the flow rate controller 15.

On the other hand, arsine (As3H) contained in the raw material supply chamber 23
Since 3) is a gaseous raw material, it is supplied directly to the growth chamber 3 via the flow rate controllers 13 and 16. At this time, the valve v10~
12 is closed.

An epitaxial thin film is formed by vapor phase molecular beam epitaxy using each raw material introduced into the growth chamber 3 via the raw material supply gas line. In this case, a thin film of A-GaAs will be grown in the growth chamber 3. Also, Ga
To grow As, close valve V7 and open valve VI.
By opening 0.21, extra-system hetrimethylaluminum is released. This growth chamber 3 is 1O-6~10-'
Thin film growth is performed at a pressure of Torr.

Hydrogen gas, ethane gas, and remaining raw materials after the reaction are discharged to the outside of the system through a growth chamber exhaust gas line consisting of 5 cold traps, a turbo molecular pump 6150, and a tally pump 62.

Further, a preparation chamber 4 is attached to the reaction chamber 3, and this preparation chamber 4 also has a preparation chamber exhaust gas line consisting of a turbo molecular pump 63 and a rotary pump 64, which communicates with the outside of the system.

On the other hand, when the raw material is not supplied to the growth chamber 3, the valve v
Close valves 4 to 9 to stop the supply of raw material gas, and close valves V10 to 1.
By opening 2 and valves V22 to 24, only the carrier gas is discharged to the outside of the system via cold trap 52 and valve V21.

[Problems to be Solved by the Invention] However, cleaning the cold trap 52 and the piping, that is, cleaning the cold trap 52 and the piping once
When removing impurities such as raw materials and oxygen, nitrogen, nitrogen compounds, and carbon compounds adhering to the cold trap 52 and inside the pipes by heating to 00 to 200°C, the gas is removed by turbo molecules in the growth chamber exhaust gas system. Since the pump 61 and the rotary pump B2 were used, undecomposed raw materials were trapped in the growth chamber exhaust gas line and remained there for a long time, causing a decrease in the degree of vacuum in the growth chamber 3 and back contamination with impurities.

Therefore, the valve V21 is opened and the cold trap 52 is opened.
A raw material exhaust gas line was installed and exhaust was carried out at normal pressure.

[Problems to be Solved by the Invention] When supplying raw materials, the upstream sides of the flow controllers 11 to 13 are pressurized to 0.3 to 1.0 Kg/cffl, so that the flow controllers 11 to 16 control the flow rate. The raw material was supplied to the growth chamber under control, but when the raw material was not supplied to the growth chamber, the pressure downstream of the flow rate controllers (4 to 16) was at normal pressure as described above.

Therefore, when the valves v10 to 12 are closed and the valves v7 to 9 are opened, the pressure upstream of the flow rate controllers 14 to 16 (normal pressure) and the pressure in the growth chamber 3 (10-6 to 10-' Torr
), and even if the flow rate is controlled by the flow rate controllers 14 to 16, the pressure in the growth chamber 4 will be abnormally high, and the raw material will flow in excessively, resulting in an overshoot at the start of thin film growth as shown in Figure 4. This will cause In order to grow a high-quality and homogeneous epitaxial thin film in a growth chamber, a certain amount of raw material must be supplied, but as mentioned above, if the flow rate is excessive, the growth rate will increase, but the thin film will become non-uniform. This results in the growth of a thin film with significant growth and damage, which is not desirable. Therefore, after opening the raw material cylinder and starting bubbling with hydrogen gas, which is a carrier gas, it takes 30 minutes to 2 hours until the raw material partial pressure in the raw material supply gas line becomes steady.

In addition, as mentioned above, during the time when raw materials are not supplied, the raw material supply gas lines and raw material exhaust gas lines are at normal pressure, so the gas flow rate is slow, and it takes time to extract the raw materials from each gas line after growth is completed. There is also the problem that raw materials adhere to the piping of each gas line. Further, the baking described above also required a considerable amount of time.

For this reason, it is conceivable to introduce the raw material exhaust gas line, which is a bypass line, from the cold trap 52 to the rotary pump G2 by opening the valve V20, but this will cause the above-mentioned problems such as a decrease in the degree of vacuum in the growth chamber 3 and back contamination with impurities. was not resolved in any way.

The present invention has been made in order to solve the problems of the prior art, and it eliminates the overshoot that occurs at the start of thin film growth, allows thin film growth, raw material extraction, and baking to be performed in a short time, and also allows the raw material to be connected to piping. It is an object of the present invention to provide a vapor phase molecular beam epitaxy (vapor phase MBE) apparatus that can prevent adhesion.

[Means for Solving the Problems] The above object of the present invention is achieved by providing a suction pump downstream of the cold trap in the raw material exhaust gas line, separately from the suction pump provided in the growth chamber exhaust gas line.

That is, the vapor phase MBE apparatus of the present invention is a vapor phase molecular beam epitaxy apparatus that uses a vapor phase material as at least a part of the raw material and grows an inorganic thin film in a growth chamber. The present invention is characterized in that a suction pump is provided downstream of the cold trap in the raw material exhaust gas line, separately from the suction pump provided in the growth chamber exhaust gas line.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 shows a MOM which is an example of the gas phase MBE apparatus of the present invention.
FIG. 2 is a schematic diagram of a BE device. In the figure, a suction pump consisting of a mechanical booster pump 65 and a rotary pump 66 is provided downstream of the cold trap 52 in the raw material exhaust gas line. The use of two pumps in this way depends on the type of thin film to be obtained in the growth chamber 3.
This is because the growth pressures in the two pumps are different, and by using the two pumps in combination, the pressure in the raw material supply line can be controlled as desired. In this way, by newly arranging a suction pump in the raw material exhaust gas line, the raw material gas supply line can be maintained at lo-3 to 10' even when the raw material gas is exhausted.
The gas flow rate of each pipe is maintained at 1-1 Torr.
It can be set to 0cc/min. Therefore, when valves VIO to VIO12 are closed and valves V7 to V9 are opened, no overshoot occurs when thin film growth starts, and the pressure immediately becomes steady as shown in FIG. 2. Along with this, the raw material gas flow rate also increases. It becomes constant.

Further, in the apparatus of the present invention, the flow rate controllers 14 to 18 as shown in FIG. 3 are not necessary, and a constant amount of raw material gas can be supplied.

In addition, there are two or more growth chamber exhaust gas lines, each with a suction pump, and one line introduces the exhaust gas from the growth chamber, and the other line introduces the raw material exhaust gas from the cold trap. Embodiments are also encompassed by the invention.

Further, although the present invention is directed to a gas-phase MBE apparatus, it is also applicable to a low-pressure MOCVD apparatus using a gas-phase material as a raw material.

[Operations and Effects] The present invention as described above provides the following operations and effects.

(1) At the start of thin film growth, the pressure immediately reaches a steady state,
Along with this, the raw material gas flow rate also becomes constant and overshoot does not occur, so that a high quality and homogeneous epitaxial thin film can be obtained.

(2) Since the raw material supply line and the raw material exhaust line are maintained in a reduced pressure state, a) the partial pressure of the raw material with respect to hydrogen gas, which is the carrier gas, can be increased, so the amount of raw material supplied can be increased; b) after the growth is completed The raw material can be removed from the piping in a short time; C) The flow rate of the raw material gas is faster, so less of the raw material gas adheres to the piping; d) Baking can be performed easily, so baking efficiency is improved; (3) Baking of the raw material supply line and the raw material exhaust line can be carried out without using a pump in the growth chamber exhaust gas line, so that a decrease in the degree of vacuum in the growth chamber and impurity back contamination do not occur.

[Examples] The present invention will be specifically described below based on Examples and Comparative Examples.

Using the MOMBE apparatus shown in FIG. 1, an epitaxial GaAs thin film was grown on a GaAs substrate wafer using trimethylgallium and arsine as raw materials (Example 1).

A micrograph of this epitaxial GaAs thin film (x
1000) is shown in FIG.

In addition, for comparison, using the MOMBE apparatus shown in Figure 3, we used trimethylgallium and arsine as raw materials, and Ga
On top of the As substrate wafer, epitaxial GaAs
A thin film was grown (Comparative Example 1).

A micrograph of this epitaxial GaAs thin film (X
1000) is shown in FIG.

As is clear from the comparison between Fig. 5 and Fig. 6, apart from the common dirt on the lens, the surface in Fig. 5 is flat with no irregularities, whereas in Fig. 6, no single crystal has grown. Gallium droplets were formed.

Furthermore, after using the apparatus shown in FIGS. 1 and 3, the degree of contamination of the piping of the raw material supply line was evaluated by quadrupole mass spectrometry, and the H20/H2 of the apparatus shown in FIG. 1 was 3. IX 10
-', whereas the H20/H2 ratio of the apparatus shown in FIG. 3 was 2.2xlO-3, meaning that the apparatus shown in FIG. 1 reduced contamination by about 1/7. In addition, CO2 and 02
A similar tendency was observed for other impurities.

[Brief explanation of drawings]

FIG. 1 shows a MOM which is an example of the gas phase MBE apparatus of the present invention.
A schematic diagram of a BE apparatus. Figure 2 is a graph showing the relationship between pressure and time when thin film growth is started using the MOMBE apparatus of Figure 1. Figure 3 is a schematic diagram of a conventional MOMBE apparatus. Figure 4 is
FIG. 3 is a graph showing the relationship between pressure and time when thin film growth is started using the MOMBE apparatus. FIG.
a Micrograph (X 1000) of the As thin film, and Figure 6 shows the epitaxial G obtained in Comparative Example 1.
a Micrograph of As thin film (X 1000). 51, 52: Cold trap 61-66: Suction pump

Claims (1)

[Claims] 1. In a vapor phase molecular beam epitaxy apparatus that uses a gas phase material as at least a part of the raw material and grows an inorganic thin film in a growth chamber, a cold trap in the raw material exhaust gas line, which is a bypass line leading from the raw material supply gas line to the outside of the system. A vapor phase molecular beam epitaxy apparatus characterized in that a suction pump is provided downstream, separately from a suction pump provided in a growth chamber exhaust gas line.