JPH07291789A - Molecular beam epitaxy apparatus - Google Patents

Abstract

PURPOSE:To grow a compd. semiconductor epitaxial crystal having high quality on a substrate by disposing a molecular beam intensity sensor in a crystal growth chamber and measuring the intensity of the molecular beam of a raw material for growth. CONSTITUTION:The molecular beam epitaxy apparatus which grows the compd. semiconductor epitaxial crystal by supplying a raw material for growth and a gaseous dopant to the surface of the substrate B in the crystal growth chamber 1 is added with the following constitution: The apparatus is provided with the molecular beam intensity sensor (a B-A type ionization vacuum gage designated as a flux monitor 21) disposed in the crystal growth chamber 1 in order to measure the intensity of the molecular beam of the raw material for growth and a controller 22 (constituted by including temp. controllers 23, 24 and power sources 27, 28) for feedback control of the intensity of the molecular beam of the raw material for growth from the measured value of the molecular beam intensity sensor 21. A plasma cell having a cylindrical magnet 17 and a high-frequency coil 19 is used as an excitation cell device 11 for supplying the nitrogen dopant.

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 raw material and a dopant gas to the surface of a substrate, and particularly to growing a II-VI group compound semiconductor epitaxial crystal. The present invention relates to a molecular beam epitaxy apparatus suitable for

[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, generally 10 ⁻⁷ to 10
^It is necessary to perform the treatment at an atmospheric pressure of about ^-10 torr. Especially when a gas is used as a dopant, it is considered that the atmospheric pressure fluctuation in the crystal growth chamber affects the molecular beam of the growth raw material. It needs to be properly controlled.

On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 62-88329 discloses, as an example of a II-VI group epitaxial crystal, zinc selenide (ZnS) on a gallium arsenide (GaAs) substrate.
A structure for growing an epitaxial crystal of e) and introducing nitrogen (N) as a dopant to obtain a p-type crystal is disclosed. Also, according to DePuydt et al. In the US, a method has been proposed in which an active nitrogen beam is generated by an rf plasma cell by the MBE method to realize nitrogen doping of 10 ¹⁸ cm ⁻³ (Appl.Phys.Lett. 57,2127
(1991)), which suggests that a low-resistance p-type crystal can be obtained.

However, since the conditions for growing the II-VI group compound semiconductor epitaxial crystal are more severe than those of other groups such as III-V group, the intensity of the molecular beam is more precise than during normal crystal growth. However, in order to generate the activated nitrogen beam by the rf plasma cell, the atmospheric pressure condition should be at least 10 ^-5.
Must be about to 10 ^-6 torr, it tends to occur a fluctuation in the molecular beam growth material generated from the Knudsen cell by the pressure variation during the plasma generation. Further, under this atmospheric pressure condition, it is difficult to measure the intensity of the molecular beam, and fluctuations occurring in the molecular beam cannot be controlled appropriately, resulting in a significant reduction in crystal quality.

On the other hand, a method of generating an activated nitrogen beam by using ECR plasma discharge or microwave discharge has been proposed (ECR plasma discharge: S. Itoh et al., For example.
See Jpn.J.Appl.Phys.31, L1361 (1992), Microwave discharge: Tsuka et al. 40th Joint Lecture on Applied Physics 31p
-ZN1), pressure slightly lower than rf plasma cell (1
Although at about 0 ^-7 torr base late) can maintain the discharge,
It is difficult to do as high concentration doping as an rf plasma cell,
Further, since the device is complicated and expensive, there are problems in maintainability and cost.

[0007]

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 to provide a molecular beam epitaxy device capable of performing the same. Another object of the present invention is to facilitate the excitation of the doping gas, to have no influence on the crystal growth conditions, and to provide a high-quality I on the substrate.
It is an object of the present invention to provide a molecular beam epitaxy device capable of growing an I-VI group compound semiconductor epitaxial crystal and having a simple structure.

[0008]

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. And a feedback control of the intensity of the molecular beam of the growth raw material from the measurement value of the molecular beam intensity sensor provided in the crystal growth chamber to measure the intensity of the molecular beam of the growth raw material and the molecular beam intensity sensor. It is achieved by providing a molecular beam epitaxy device characterized by having a control device for

[0009]

According to the above structure, the molecular beam intensity sensor is provided in the crystal growth chamber to measure the intensity of the molecular beam of the growth raw material, so that the intensity of the molecular beam can be stably controlled from the measured value, and the quality of the beam can be constantly maintained. Crystals can be obtained.
In particular, by generating plasma by a plasma cell (hereinafter, referred to as a helicon plasma cell in the present specification) including a magnet and a high frequency coil, low pressure (1
Even in a state of 0 ^-7 to 10 ^-9 torr, a plasma discharge emission intensity higher than that of an rf plasma cell by an order of magnitude is obtained with a low high frequency power (5 W to 300 W). Here, since it is easier to measure the molecular beam intensity at a low pressure, the molecular beam intensity is monitored when growing a II-VI group compound semiconductor epitaxial crystal, as compared with the conventional crystal growth under high pressure conditions. The feedback control can be easily performed.

[0010]

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 first 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 Knudsen cells (hereinafter abbreviated as K cells in the present specification) opening toward the substrate B are provided at positions in the lower portion of the crystal growth chamber 1 that are substantially opposed to the substrate B.
7 and 8 are provided. These K cells 7 and 8 are crucibles 7 a and 8 a that open toward the substrate B and these crucibles 7 and 8.
It has heaters 7b and 8b for heating a 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 at positions where the openings of the K cells 7 and 8 are covered and positions where the openings are not covered. Rotatably supported between the crucibles 7a and 8 by selectively rotating the drive shafts 9a and 10a from the outside.
The growth raw material received in a is irradiated onto the substrate B as a molecular beam.

Apart from the K cells 7 and 8, a nitrogen plasma excitation cell device 11 is provided at a position below the crystal growth chamber 1 and 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 helicon plasma cell equipped with. 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 the control device 22. The control device 22 is connected to temperature control devices 23 and 24 corresponding to the K cells 7 and 8, respectively. The temperature control devices 23 and 24 are used in the crucibles 7a and 8a of the K cells 7 and 8, respectively.
A thermocouple 25 for measuring the temperature of each growth raw material inside,
26 and the power supplies 27 and 28 of the heaters 7b and 8b, and the controller 22 controls the temperature controller 23 and the temperature controller 23 according to the molecular beam intensity measured by the flux monitor 21.
The set temperature is output to 24 as a command value, and the temperature adjusting devices 23 and 24 measure the temperatures inside the crucibles 7a and 8a of the K cells 7 and 8 with the thermocouples 25 and 26, respectively.
By individually controlling b and 8b with the power supply devices 27 and 28, the temperature inside the crucibles 7a and 8a, that is, the intensity of each molecular beam is feedback-controlled.

The operation 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.

Next, after a lapse of a predetermined time, the shutter 9 is first opened and closed, and the flux monitor 21 controls the controller 22, the temperature controller 23 and the power supply 27 so that the molecular beam of selenium is stabilized. Next, the shutter 10 is opened and closed, and the flux monitor 21 controls the zinc oxide molecular beam by the controller 22, the temperature controller 24, and the power supply 28 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 is stabilized at an intensity of 1: 1, the flux monitor 21 is retracted to a position near the left wall surface in FIG.
10 is closed together, the shutter 11a is opened to generate a high frequency in the excitation cell device 11 (5 W to 300 W), and nitrogen gas is enclosed in the casing 12 at a flow rate in the range of 0.01 cc / min to 0.5 cc / min. It is supplied to the plasma generating chamber. Here, high-density nitrogen plasma is generated by the interaction between the magnetic field generated by the magnet 17 and the high-frequency coil 19. After that, when the nitrogen plasma is stabilized, the shutters 9 and 10 are opened, and finally the shutter 6 is opened to grow an epitaxial crystal of zinc selenide on the surface of the substrate B and nitrogen is introduced as a dopant into the p-type crystal. Can be obtained. With the p-type crystal thus formed, a carrier concentration of 1 × 10 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.

FIG. 2 is a schematic sectional view showing a schematic structure of an MBE apparatus according to the second embodiment to which the present invention is applied. The same parts as those in the first embodiment are designated by the same reference numerals. Then
Detailed description thereof will be omitted.

In this embodiment, the flux monitors 31 and 3 are used.
2 is fixed at a position directly above the K cells 7 and 8 that does not hinder the crystal growth. Further, the flux monitor 31 corresponds to the K cell 7 and has a cylindrical cover 3 that opens toward this.
3 and the flux monitor 32 corresponds to the K cell 8 and is covered with a tubular cover 34 that opens toward this. As a result, each K cell 7, 8 is highly directional.
The intensity of the molecular beam from can be measured. Further, cooling pipes 35 and 36 are wound around the cylindrical covers 33 and 34, respectively. By cooling the cylindrical covers 33 and 34 by this, the growth raw materials and the like adhering to the inner and outer surfaces thereof are re-evaporated and the flux monitors. It is designed to prevent the measurement accuracy of 31 and 32 from being lowered.

The flux monitors 31 and 32 are connected to a control device 22 similar to that of the first embodiment, and the control device 22 controls the temperature control device 23, in accordance with the molecular beam intensity measured by the flux monitors 31 and 32. The set temperature is output to 24 as a command value, and the temperature adjusting devices 23 and 24 determine the temperature inside the crucibles 7a and 8a of the K cells 7 and 8 by the thermocouple 25 and
By individually controlling the heaters 7b and 8b with the power supply devices 27 and 28 while measuring 26, the temperature inside the crucibles 7a and 8a, that is, the intensity of each molecular beam is feedback-controlled. Other structures are first
It is similar to the embodiment of.

The operating procedure of this embodiment will be described below. The selenium and zinc are received in the crucibles 7a and 8a, and the substrate B
Is held in the holder 3 and vacuumed to heat the substrate B, selenium, and zinc in the same manner as in the first embodiment.

Next, after a lapse of a predetermined time, the shutter 9,
10 is opened / closed, and the intensity of each molecular beam is measured by the flux monitors 31 and 32 so that the molecular beams of selenium and zinc are stabilized, and the control device 22 and the temperature control devices 23 and 24 are used.
And the power supply devices 27 and 28. Then, a high frequency is generated in the excitation cell device 11, and nitrogen gas is supplied to the plasma generation chamber defined inside the casing 12.
After that, when the nitrogen plasma is stabilized, the shutter 6 is opened to grow an epitaxial crystal of zinc selenide on the surface of the substrate B while introducing nitrogen as a dopant into the epitaxial crystal. At this time, in the present embodiment, as described above, the flux monitors 31 and 32 are fixed at positions that do not hinder the crystal growth.
1, 32 can continue to measure each molecular beam intensity, and the control device 22, the temperature control devices 23, 24, and the power supply device 27 so that the molecular beams of selenium and zinc are stabilized.
You can continue to control with 28. This allows
The intensity of each molecular beam can be controlled more appropriately than in the first embodiment, and the crystal quality is improved. In the present embodiment, the flux monitor is not directly irradiated with the molecular beam to measure its intensity, but the amount (intensity) of molecules advancing directly above due to evaporation of the growth raw material is approximately proportional to the molecular beam intensity. Therefore, a measurement result similar to that of actually measuring the intensity of the molecular beam can be obtained.

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

[0025]

As is apparent from the above description, according to the molecular beam epitaxy apparatus of the present invention, the growth raw material is obtained from the measured value of the sensor for measuring the intensity of each molecular beam provided in the crystal growth chamber. By feedback controlling the intensity of the molecular beam of, the intensity of the molecular beam becomes stable, and a good quality crystal can always be obtained. In particular,
By generating plasma with a helicon plasma cell, even if the pressure is low, high plasma discharge emission intensity can be obtained with low high-frequency power, and the dopant gas can be easily excited, so that the degree of vacuum can be increased. That is, since the intensity of the molecular beam can be easily measured and the feedback control can be precisely performed to stabilize the molecular beam of the growth raw material, a high-quality II-VI group compound semiconductor epitaxial crystal can be easily grown.

[Brief description of drawings]

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

FIG. 2 is a sectional view similar to FIG. 1, showing a schematic configuration of a molecular beam epitaxy apparatus according to a second embodiment of the present invention.

[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 11 excitation cell device 11a shutter 12 casing 12a Orifice 13 Nitrogen gas supply port 14 Pipeline 15 Flow control device 16 Pressure reducing valve 17 Magnet 18 Nitrogen cylinder 19 High frequency coil 20 High frequency generator 21 Flux monitor 22 Control device 23, 24 Temperature control device 25, 26 Thermocouple 27, 28 Heater Power supply device 31, 32 Flux monitor 33, 34 Cylindrical cover 35, 36 Cooling pipe

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[Procedure amendment]

[Submission date] August 3, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

[0009]

According to the above structure, the molecular beam intensity sensor is provided in the crystal growth chamber to measure the intensity of the molecular beam of the growth raw material, so that the intensity of the molecular beam can be stably controlled from the measured value, and the quality of the beam can be constantly maintained. Crystals can be obtained.
In particular, by generating plasma by a plasma cell (hereinafter, referred to as a helicon plasma cell in the present specification) including a magnet and a high frequency coil, low pressure (1
Even in a state of 0 ^-7 to 10 ^-9 torr), a plasma discharge emission intensity higher than that of an rf plasma cell by an order of magnitude can be obtained with a low high frequency power (5 W to 300 W) (see FIG. 3).
See) . Here, since it is easier to measure the molecular beam intensity at a low pressure, the molecular beam intensity is monitored when growing a II-VI group compound semiconductor epitaxial crystal, as compared with the conventional crystal growth under high pressure conditions. The feedback control can be easily performed.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

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

FIG. 2 is a sectional view similar to FIG. 1, showing a schematic configuration of a molecular beam epitaxy apparatus according to a second embodiment of the present invention.

FIG. 3 shows a helicon plasma cell and an rf plasma cell.
It is a graph for comparing luminescence intensity.

[Description of Reference Signs] 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 11 excitation cell Device 11a Shutter 12 Casing 12a Orifice 13 Nitrogen gas supply port 14 Pipeline 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 22 Control device 23, 24 Temperature control device 25, 26 Thermoelectric Pair 27, 28 Heater power supply 31, 32 Flux monitor 33, 34 Cylindrical cover 35, 36 Cooling pipe

Claims (4)

[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, the intensity of a molecular beam of the growth raw material being measured. In order to do so, a molecular beam intensity sensor is provided in the crystal growth chamber, and a control device for feedback-controlling the intensity of the molecular beam of the growth raw material from the measured value of the molecular beam intensity sensor is used. apparatus. 2. The molecular beam epitaxy apparatus is adapted to generate a molecular beam by heating a growth raw material with a heater, and the control apparatus controls a heating state by the heater to cause the molecular beam to grow. 2. The molecular beam epitaxy apparatus according to claim 1, wherein the intensity of the molecular beam epitaxy is controlled. 3. The molecule according to claim 1, wherein the molecular beam intensity sensor is composed of an ionization vacuum gauge, and the molecular beam intensity is obtained from the degree of vacuum measured by the ionization vacuum gauge. Line epitaxy equipment. 4. The growth raw material comprises a Group II element and a Group VI element, the dopant comprises nitrogen, the compound semiconductor epitaxial crystal comprises a II-VI compound semiconductor epitaxial crystal, and the nitrogen dopant is supplied. The excitation cell device has a bottomed cylindrical casing having a nitrogen gas supply port and opening to the crystal growth chamber side, a magnet provided at the bottom of the casing, and a high frequency wave disposed on the outer periphery of the casing. The molecular beam epitaxy apparatus according to any one of claims 1 to 3, comprising a plasma cell including a coil.