JPH07288230A - Molecular-beam epitaxy apparatus - Google Patents

Abstract

PURPOSE:To provide a molecular-beam epitaxy apparatus, which can grow a high-quality compound semiconductor epitaxial crystal on a substrate without troubles in the opening/closing operations of K cells in the crystal growing. CONSTITUTION:Hot-wire heaters 9b and 10b are attached to shutters 9 and 10, which are movably supportted between the closing positions and the opening positions of Knudsen cells 7 and 8, and the shutters can be selectively heated. Thus, the attachment of growing raw material to the shutters can be prevented, or the attached growing raw material can be evaporated again. The closure of the openings of the Knudsen cells and the defective opening/closing operations of the shutters caused by the falling of the attached amterial can be prevented. Therefore, the molecular beams are stabilized, and the excellent crystalls are always obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molecular beam epitaxy apparatus for growing a compound semiconductor epitaxial crystal by supplying a growth material and a dopant gas to the surface of a substrate.

[0002]

2. Description of the Related Art A molecular beam epitaxy method (hereinafter abbreviated as MBE method in this specification) is generally known as one of epitaxial crystal growth methods for compound semiconductors.

In the above MBE method, a Knudsen cell (hereinafter, abbreviated as K cell in the present specification) which holds a substrate in a crystal growth chamber and is composed of a crucible and a heater provided at a position opposite to the substrate is held. Therefore, the growth raw material is irradiated onto the surface of the substrate as a molecular beam to grow crystals on the surface of the substrate. In addition, a p-type or n-type semiconductor crystal can be grown by introducing a dopant as needed.

Here, the K cell is opened upward and the substrate is set downward so that the fragments of the growth material solidified in other parts do not drop and adhere to the substrate, and the substrate is set downward so as to face downward. There is an MBE device that irradiates a molecular beam from the side. Further, in the MBE apparatus, a shutter that can be opened and closed is provided at the opening of the K cell so that the molecular beam is not accidentally irradiated toward the substrate surface.

However, when the crucible for closing the shutter of the K cell is heated, the shutter is irradiated with the molecular beam, and the growth raw material is deposited and deposited. When the shutter opens and closes, the attached matter comes into contact with the vicinity of the opening of the K cell,
There is a problem that it becomes difficult to smoothly perform the opening / closing operation, and in some cases, film formation cannot be performed. Further, if this deposit falls on the opening of the K cell, it is possible that the opening is blocked and a good molecular beam cannot be obtained, and the quality of the crystal is significantly deteriorated.

Therefore, there is an MBE device in which the entire device is obliquely arranged so that the opening of the K cell is not located directly below the shutter, but the problem that the opening and closing operation is defective due to the deposit on the shutter cannot be solved.

It is known that the above-mentioned problem that the growth material is attached to the shutter remarkably appears particularly in a molecular beam epitaxy apparatus for growing a II-VI group compound semiconductor epitaxial crystal.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the prior art as described above, and its main purpose is to grow a high-quality compound semiconductor epitaxial crystal on a substrate. It is an object of the present invention to provide a molecular beam epitaxy device which can be formed and does not cause a problem in the opening / closing operation of the shutter of the K cell.

[0009]

According to the present invention, there is provided a molecular beam epitaxy apparatus for growing a compound semiconductor epitaxial crystal by supplying a growth raw material and a dopant gas to a surface of a substrate in a crystal growth chamber. Between at least one Knudsen cell provided with a crucible for receiving a growth material inside and opening into the crystal growth chamber, and between a position that closes the opening of the Knudsen cell and a position that does not close the same. It is achieved by providing a molecular beam epitaxy device characterized in that it has a movably supported shutter and a heating wire attached to the shutter for selectively heating the shutter.

[0010]

According to the above-described structure, by heating the shutter with the heat ray, it is possible to prevent the growth raw material from adhering to the shutter or to re-evaporate the attached growth raw material.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic sectional view showing a schematic structure of a molecular beam epitaxy apparatus (MBE apparatus) in a preferred embodiment to which the present invention is applied. This example is an MBE apparatus for growing an epitaxial crystal of zinc selenide (ZnSe) on a gallium arsenide (GaAs) substrate and introducing nitrogen (N) as a dopant to obtain a p-type crystal.

With the ultra-high vacuum exhaust device 2, 10 ^-7 to 10 ^-9
The substrate B is held by the holder 3 in the crystal growth chamber 1 capable of maintaining a high vacuum of about torr so that the processed surface faces downward. A heater 5 for heating the substrate is provided on the base end side of the holder 3, that is, on the upper side in the drawing. Further, the disk-shaped main shutter 6 has a position where the film formation of the substrate B is started, that is, a position where the processed surface of the substrate B is not covered, and a position where film formation is stopped, that is, a position where the processed surface of the substrate B is covered. It is rotatably supported between the two, and the film formation can be selectively started / stopped by rotating the drive shaft 6a from the outside.

Two K cells 7 and 8 opening toward the substrate B are provided at a position in the lower part of the crystal growth chamber 1 which is substantially opposed to the substrate B. These K cells 7 and 8 have crucibles 7a and 8a opening toward the substrate B and heaters 7b and 8b for heating these crucibles 7a and 8a. Further, disk-shaped shutters 9 and 10 similar to the main shutter 6 are provided in the openings of the K cells 7 and 8 for the K cells.
The cells 7 and 8 are rotatably supported between a position that covers the openings and a position that does not cover the openings, and the drive shafts 9a and 10a are selectively rotated from the outside to selectively select the crucibles 7a,
Substrate B using the growth raw material received in 8a as a molecular beam
It is designed to irradiate to. Further, as shown in FIG. 2, heat ray heaters 9b and 10b connected to an external power source and a control device (not shown) are spirally arranged on the surfaces of the shutters 9 and 10 facing the substrate. The shutters 9 and 10 are selectively heated.

In addition to the K cells 7 and 8, a nitrogen plasma excitation cell device 11 is provided in the lower portion of the crystal growth chamber 1 at a position substantially facing the substrate B. This excitation cell device 11 has a bottomed cylindrical casing 12 made of high-purity ceramic that opens to the crystal growth chamber 1 side and forms a plasma generation chamber inside, and a casing 12 that opens to the bottom of the casing 12 and has a tube shape. A cylindrical magnet provided at the bottom of the casing 12 so as to surround the nitrogen gas supply port 13 connected to the nitrogen cylinder 18 via the passage 14, the flow rate control device 15, and the pressure reducing valve 16 and the pipe passage 14. 17 and a high-frequency coil 19 arranged on the outer periphery of the casing 12 and connected to the high-frequency generator 20.
And a plasma cell having. The opening of the casing 12 is provided with an orifice 12a for narrowing it down. A shutter 11a similar to the above shutter is provided at the opening of the casing 12.

On the other hand, in the crystal growth chamber 1, there is provided a flux monitor 21 as a molecular beam intensity sensor consisting of a known BA type ionization vacuum gauge for measuring the intensity of each molecular beam from the degree of vacuum. . Flux monitor 21
Is moved as shown by an arrow between a position where each molecular beam is directly irradiated, that is, a position immediately before the main shutter 6, and a position where each molecular beam is not directly irradiated, that is, a position near the left wall surface in FIG. Is ready to go. Further, the flux monitor 21 is connected to a control device (not shown), and the heaters 7 of the K cells 7 and 8 are controlled by this control device.
By controlling b and 8b to individually control the temperatures in the crucibles 7a and 8a, the temperatures in the crucibles 7a and 8a, that is, the respective molecular beam intensities are feedback-controlled.

The operating procedure of this embodiment will be described below. First, selenium (Se) is received in the crucible 7a and zinc (Zn) is received in the crucible 8a, the substrate B is held downward by the holder 3, and the inside of the crystal growth chamber 1 is evacuated by the ultrahigh vacuum exhaust device 2 to obtain 10 Maintain a high vacuum of about ^-7 to 10 ^-9 torr. Then, the substrate B is rotated and heated, and selenium and zinc are heated. At this time, each shutter 6,
9, 10, 11a are still closed. Further, the shutters 9 and 10 are heated by the heat ray heaters 9b and 10b, and selenium and zinc are prevented from adhering to the shutters 9 and 10, respectively.

Next, after a lapse of a predetermined time, the shutter 9 is first opened and closed, and the flux monitor 21 controls so that the selenium molecular beam is stabilized. Next, the shutter 10 is opened and closed, and the flux monitor 21 controls so that the zinc molecular beam is stabilized. At this time, it is advisable to control the molecular beams of selenium and zinc to be stable at an intensity of 1: 1. When each molecular beam stabilizes at an intensity of 1: 1, the flux monitor 21 is retracted to a position near the left wall surface in FIG. 1 where the molecular beam is not directly irradiated, both shutters 9 and 10 are closed, and shutter 11a is opened to open the excitation cell device. A high frequency is generated at 11 (5 W to 300 W), and nitrogen gas is supplied to the plasma generation chamber defined in the casing 12 at a flow rate in the range of 0.01 cc / min to 0.5 cc / min. Here, the magnetic field generated by the magnet 17 and the high frequency coil 1
A high-density nitrogen plasma is generated by the interaction with 9.

Thereafter, when the nitrogen plasma is stabilized, the shutters 9 and 10 are opened, and finally the shutter 6 is opened to open the substrate B.
It is possible to obtain a p-type crystal by introducing nitrogen as a dopant therein while growing an epitaxial crystal of zinc selenide on the surface of. At this time, if there is almost no temperature change in the crystal growth chamber 1, the heat ray heaters 9b and 10b of the shutters 9 and 10 may be stopped, and the stop causes the temperature change in the crystal growth chamber 1. In such a case, the crystal growth may be performed while the hot wire heaters 9b and 10b are operated. The p-type crystal thus formed has a size of 1 × 1.
A carrier concentration of 0 ¹⁸ cm ^-3 was obtained.

Here, if the high frequency power is less than 5 W, no electric discharge occurs, and if it exceeds 300 W, nitrogen atoms are excessively introduced into the crystal and the quality of the crystal deteriorates. Also, if the nitrogen gas flow rate is less than 0.01 cc / min, it becomes difficult to maintain the discharge, and if it exceeds 0.5 cc / min, MB
There is a concern that the pressure may be deviated from the crystal growth condition of the E apparatus.

In the above embodiment, the heat ray heaters 9b and 1b are provided when the shutters 9 and 10 of the K cells 7 and 8 are closed.
0b is operated to heat the shutters 9 and 10 to prevent the growth material from adhering. However, when the shutters 9 and 10 are open, the heat ray heaters 9b and 10b are operated to adhere to the shutters 9 and 10. Needless to say, the same action and effect can be obtained by re-evaporating the grown growth material. Further, in this embodiment, the heat ray heater is provided only for each shutter 9, 10 of each K cell 9, 10, but if a similar heater is also provided for the main shutter, the opening and closing of the main shutter and the K cell from the main shutter may occur. It is also possible to prevent deposits from falling onto the openings of the excitation cell device.

Further, although zinc was used as the group II element and selenium was used as the group VI element in the above-mentioned examples, any one of cadmium (Cd), zinc (Zn) and magnesium (Mg) as the group II element, VI II-VI containing any one or any of sulfur (S), selenium (Se), tellurium (Te), and manganese (Mn) as a group element
The same effect can be obtained by using a group mixed crystal. Further, in the above embodiment, gallium arsenide (GaAs) is used as the crystal growth substrate.
Although a substrate is used, a suitable thin film crystal (for example, a gallium arsenide film obtained by epitaxial crystal growth) may be formed on a ZnSe, GaP or gallium arsenide (GaAs) substrate.

[0023]

As is apparent from the above description, according to the molecular beam epitaxy apparatus according to the present invention, a shutter movably supported between a position where the opening of the Knudsen cell is closed and a position where it is not closed is provided. By attaching a heat ray heater so that the shutter can be selectively heated, it is possible to prevent the growth raw material from adhering to the shutter, or to re-evaporate the attached growth raw material, and Since it is possible to prevent the opening of the K cell from being closed and the opening / closing operation of the shutter to be defective, the molecular beam becomes stable, and a good quality crystal can always be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a schematic configuration of a molecular beam epitaxy apparatus in a preferred embodiment according to the present invention.

FIG. 2 is a plan view of a shutter of the Knudsen cell of FIG.

[Explanation of symbols]

 1 crystal growth chamber 2 ultra-high vacuum exhaust device 3 holder 5 heater 6 main shutter 6a drive shaft 7, 8 Knudsen cell 7a, 8a crucible 7b, 8b heater 9, 10 shutter 9a, 10a drive shaft 9b, 10b heat wire heater 11 excitation cell Device 11a Shutter 12 Casing 12a Orifice 13 Nitrogen gas supply port 14 Pipe line 15 Flow rate control device 16 Pressure reducing valve 17 Magnet 18 Nitrogen cylinder 19 High frequency coil 20 High frequency generator 21 Flux monitor

Claims (2)

[Claims] 1. A molecular beam epitaxy apparatus for growing a compound semiconductor epitaxial crystal by supplying a growth raw material and a dopant gas to a surface of a substrate in a crystal growth chamber, wherein the molecular beam epitaxy device has an opening inside the crystal growth chamber and an inside. At least one or more Knudsen cells provided with crucibles for receiving the growth material; a shutter movably supported between a position that closes the opening of the Knudsen cells and a position that does not close the Knudsen cell; And a heating wire attached to the shutter for heating the molecular beam epitaxy apparatus. 2. The molecular beam epitaxy apparatus according to claim 1, wherein the growth raw material is composed of a group II element and a group VI element, and the compound semiconductor epitaxial crystal is composed of a II-VI group compound semiconductor epitaxial crystal. .