JPH05243150A - Molecular beam epitaxial growth and device thereof - Google Patents

Abstract

PURPOSE:To perform a cleaning treatment of the surface of a substrate, which is performed prior to the emission of a molecular beam, at a lower temperature in a molecular beam epitaxial growth on a III-V compound semiconductor, such as GaAs, and to suppress low an interfacial level density for performing the epitaxial growth. CONSTITUTION:A laser beam is applied to hydrogen, which is fed to a surface 12' of a GaAs substrate 12 held in a vacuum in a surface treatment chamber 5 from a gas feeding system 1, from a laser 2 to produces radicals and the substrate surface 12' is treated with gas containing these radicals. Thereby, while a vacuum state is held, the substrate 12 is transferred to a growth chamber 8 via transfer chambers 11a and 11b and a molecular beam is emited on the substrate surface treated in the chamber 8 to form an epitaxial layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for obtaining an epitaxial layer by injecting a molecular beam into a III-V group compound semiconductor substrate, and more particularly to a surface level and an interface for application to a semiconductor device. The present invention relates to a method and an apparatus for forming a semiconductor epitaxial layer having a low number of levels, that is, good interface characteristics.

[0002]

2. Description of the Related Art Conventionally, in a molecular beam epitaxial growth method (MBE method) using a substrate of a III-V group compound semiconductor such as GaAs, the substrate is heat treated in situ in an ultrahigh vacuum or in an As atmosphere before the epitaxial growth. Has been done. By this heat treatment, the substrate surface to be epitaxially grown is cleaned.

On the other hand, recently, "GaAs and Rel
arated Compound, Atlanta, Geo
rgia, 1988, pp. 47-52 ", an MBE method using three-chamber type etching molecular beam epitaxial growth has been developed. In this method, Cl ₂ gas is used in one of the three dry etching chambers to perform thermal etching or EC.
The surface of the substrate is cleaned by R plasma etching.

In addition, "GaAs and Relate
d Compound, Jersey, 1990, p.
p. 111-116 ”is a 2-chamber ultra-high vacuum MBE.
A method of irradiating a substrate with Se molecular beam in one chamber of the apparatus to terminate the dangling bond on the GaAs surface to inactivate it and to form an a-Se protective film has been reported. There is.

[0005]

In the conventional heat treatment generally performed, a high temperature, for example, 500 ° C. to 700 ° C. is used.
The surface of the substrate may be damaged by ° C. If the heat treatment becomes excessive in order to sufficiently clean the surface, the surface will be damaged in this way and the surface cannot be stabilized.On the other hand, if the heat treatment is performed so as not to damage the surface, Often, the cleaning was inadequate.

In the three-chamber type apparatus described above, C
In ECR plasma etching with l ₂ , impurities such as O, C and Cl remained on the substrate, producing deep levels. On the other hand, in the above literature, thermal etching using Cl ₂ brings a clean surface to the substrate, but there is a possibility that the heat treatment may damage the substrate surface.

[0007] Further, the above-mentioned document concerning the Se protective film is
No mention is made of the application of Se films to molecular beam epitaxial growth.

An object of the present invention is to use III-V such as GaAs.
In the molecular beam epitaxial growth of a group compound semiconductor, the cleaning treatment of the substrate surface, which is performed prior to the molecular beam irradiation, can be effectively performed at a lower temperature, and as a result, the epitaxial growth is performed while suppressing the interface state density to be low. It is to provide a method and an apparatus therefor.

[0009]

In the molecular beam epitaxial method according to the first aspect of the present invention, the surface of a III-V group compound semiconductor substrate held in vacuum is charged with at least one of hydrogen and a hydrogen compound of a group V element. And a step of irradiating the treated substrate surface with a molecular beam to form an epitaxial layer while maintaining a vacuum state. In the first invention, hydrogen, a hydrogen compound of a group V element, or a mixture thereof is used for radical generation.

III-V usable in the first invention
The group compound semiconductor is not particularly limited, but a compound semiconductor that is often used is, for example, GaA.
Examples thereof include s, GaP, InSb, InP, InAs, AlAs, and mixed crystals thereof (for example, Al _1-x Ga _x As and In _1-x Ga _x As (0 <x <1)).

Further, the hydrogen compound of the group V element is, for example, AsH ₃ when the group V element is As, PH ₃ when it is P,
In the case of Sb, there is SbH ₃ .

[0012] A radical is a molecule or atom having an unpaired electron and is generally produced by photolysis, radiolysis, electrolysis, thermal decomposition or chemical reaction of a molecule. The method of the present invention is characterized in that the radicals are generated by photolysis or photochemical reaction. Further, in the method of the present invention, at least hydrogen radicals can be generated by photolysis or photochemical reaction.

As a means for photoexciting molecules for radical generation by such photolysis or photochemical reaction,
For example, a laser and a mercury lamp can be used.

When photoexciting hydrogen molecules to generate radicals, for example, light in the ultraviolet region is preferable, and the light in such a region can be efficiently generated by, for example, an excimer laser.

When photo-exciting a hydrogen compound of a group V element to generate radicals, for example, light in the ultraviolet region is preferable, and light in such a region can be efficiently generated by, for example, an excimer laser. You can

According to a second invention, there is also provided an apparatus for carrying out the method of the first invention. This device
An apparatus for irradiating a substrate with a molecular beam to form an epitaxial layer on the substrate, comprising a reaction chamber for accommodating the substrate and exposing the surface of the substrate to radicals generated by light irradiation, and a reaction chamber. A first exhaust system for exhausting gas, gas supply means for supplying a gas for radical formation to the reaction chamber,
A light irradiation means for irradiating the gas supplied from the gas supply means to the reaction chamber to optically excite molecules in the gas, and a growth chamber for accommodating the substrate processed in the reaction chamber and performing molecular beam epitaxial growth. And a second exhaust system for exhausting the growth chamber, and a transfer chamber for connecting the reaction chamber and the growth chamber while maintaining a vacuum state and transferring the substrate from the reaction chamber to the growth chamber.

In the apparatus according to the second aspect of the invention, the position at which the gas is irradiated with the light from the light irradiation means needs to be determined in consideration of the life of the radicals generated. For example, the surface of the substrate to be processed in the reaction chamber. It can be at any suitable position in the space facing.

When the light for generating radicals is introduced into the reaction chamber, the light irradiation means is provided with a light source, an optical system for guiding the light from the light source to the reaction chamber, and an optical window provided in the reaction chamber. You can

The light source included in the light irradiation means may be, for example, a laser, a mercury lamp or the like. The optical system may include a lens, a reflecting mirror, an optical waveguide, or other means for guiding the light from the light source to a predetermined position with appropriate intensity.

Further, in the apparatus according to the present invention, each of the first and second exhaust systems can be provided with a vacuum pump and its peripheral device for performing exhaust.

[0021]

According to the first aspect of the invention, radicals (especially hydrogen radicals) reach the surface of the substrate held in a vacuum, and the chemically active radicals eliminate surface contaminants such as adsorbed molecules. To be done. Further, in this surface treatment, the gas containing radicals simultaneously supplies atoms. This atom terminates and deactivates the surface dangling bond. As a result of such a process, a stable and clean substrate surface can be obtained.

Further, in the first invention, at least one of hydrogen and a hydrogen compound of a group V element is used for radical generation, and these molecules are photoexcited by light irradiation. Molecules that are electronically excited by photoexcitation are
It is efficiently converted into radicals and acts on the cleaning of the substrate surface. Since such a photoexcitation process is used, the surface treatment of the substrate can be performed at a temperature lower than the conventional one, for example, 200 ° C. to 300 ° C., and damage to the substrate due to heat is further reduced.

Further, in the photoexcitation, the excited state can be easily controlled by controlling the light energy to be applied, so that the surface treatment can be easily changed according to the property of the substrate surface. In such a case, laser light is particularly useful.

Further, the radical treatment by light irradiation can considerably reduce the damage of the substrate as compared with the direct plasma treatment and the remote plasma treatment.

If hydrogen is used in radical generation, oxygen and the like on the substrate surface can be removed from the reducing action. On the other hand, if a hydrogen compound of the group V element is used in radical generation, it is possible to prevent the group V element, which is a volatile element, from coming off from the substrate. Furthermore, in order to obtain both effects, hydrogen and a group V element can be mixed and used in an appropriate ratio.

Furthermore, in the first invention, after the surface treatment with a gas containing radicals, while maintaining a vacuum state,
Continuously shifts to epitaxial growth. Therefore, after the surface treatment, the epitaxial layer can be formed by the MBE method without contaminating the substrate surface.

In the apparatus according to the second aspect of the invention, first, the substrate can be housed in the reaction chamber, and the reaction chamber can be evacuated by the first exhaust system. Then, the gas for supplying radicals can be supplied to the reaction chamber from the gas supply means.

Since the gas to be supplied can be irradiated with light from the light irradiation means, the gas can be photoexcited to generate radicals. The gas containing radicals is
It can be supplied to the surface of the substrate in the reaction chamber to treat the surface of the substrate. Thereby, the surface of the substrate can be cleaned.

After that, the substrate can be transferred from the reaction chamber through the transfer chamber to the growth chamber that has been evacuated by the second exhaust system while maintaining the vacuum state. Thus, the substrate is housed in the growth chamber with its surface kept clean. As described above, in the apparatus according to the second aspect of the present invention, the substrate surface on which the epitaxial layer is to be formed can be cleaned with the gas containing radicals, and then the MBE method can be performed without contaminating the substrate surface. ..

[0030]

EXAMPLE FIG. 1 is a schematic view showing a specific example of an epitaxial growth apparatus according to the present invention.

Referring to FIG. 1, in a molecular beam epitaxial device 10, a preparation chamber 7 is provided at the center. An ultra-high vacuum pump 9a is connected to the preparation chamber 7, and the inside thereof is exhausted. One end of the preparation chamber 7 is connected to the surface treatment chamber 5 by the first transfer chamber 11a, and the other end is connected to the growth chamber 8 by the second transfer chamber 11b. Gate valves 6a and 6b are provided in the first transfer chamber 11a and the second transfer chamber 11b, respectively, so that the preparation chamber 7 and the surface treatment chamber 5 and the preparation chamber 7 and the growth chamber 8 can be separated from each other. ..

The surface treatment chamber 5 is provided with a susceptor 4 for mounting a substrate. In the susceptor 4,
A motor (not shown) for rotating the substrate is provided. An ultrahigh vacuum pump 9b is attached to the surface treatment chamber 5.

Further, the surface treatment chamber 5 is provided with a view port 3 as an optical window for taking in a light beam from the outside, and a gas supply system having a gas cylinder 1a, a valve 1b, a mass flow controller 1c and a nozzle 1d. 1 is connected. The nozzle 1d is configured to blow a gas toward the susceptor 4 in the surface treatment chamber 5.

On the other hand, outside the surface treatment chamber 5, an excimer laser 2 is provided so that the inside of the chamber can be irradiated with a light beam through the view port 3. Further, between the excimer laser 2 and the viewport 3, the excimer laser 2
A lens 14 is provided to focus the light from the.

The growth chamber 8 is for carrying out the MBE method, and although not shown, a cell for ejecting a molecular beam and M
The usual equipment necessary for the BE method is provided. An ultrahigh vacuum pump 9c is also attached to the growth chamber 8.

In the apparatus constructed as described above, the substrate is first accommodated in the preparation chamber 7, and then the substrate 1 is removed from the preparation chamber 7.
2 is moved to and placed on the susceptor 4 of the surface treatment chamber 5, and the inside of the surface treatment chamber 5 is evacuated by the ultrahigh vacuum pump 9b. At this time, the gate valve 6a is closed and the preparation chamber 7 and the surface treatment chamber 5 are completely isolated. Then, from the gas supply system 1 to the surface treatment chamber 5
A gas for radical generation is supplied to. At this time, the ultraviolet light from the excimer laser 2 is incident on the surface treatment chamber 5 in parallel with the surface 12 ′ of the substrate 12. This ultraviolet light is applied between the nozzle that supplies the gas toward the substrate and the surface of the substrate. As a result, the ultraviolet light irradiates the gas from the gas supply system 1 to generate radicals. The generated radicals reach the substrate surface 12 '. At this time, the substrate is exposed to radicals and surface-treated while being rotated by a motor (not shown).

After the surface treatment is sufficiently performed, the laser irradiation and the gas supply are stopped, and the surface treatment chamber 5
The inside is returned to the vacuum state when it was first evacuated.

After that, the gate valve 6a is opened to connect the preparation chamber 7 and the surface treatment chamber 5, which have been previously evacuated by the ultrahigh vacuum pump 9a. Then, the substrate 12 is moved to the preparation chamber 7 through the first transfer chamber 11a. Next, the gate valve 6a is closed, and the preparatory chamber 7 is set to an ultra high vacuum (-10 ^-11 m
After reaching b), the gate valve 6b is opened, and the growth chamber 8 is previously made to have an ultrahigh vacuum by the ultrahigh vacuum pump 9c.
Then, the substrate 12 is moved through the second transfer chamber 11b. When the substrate is housed in the growth chamber 8, the gate valve 6b is closed and the MBE method is started. As described above, the epitaxial layer is formed on the substrate.

Example 1 MBE growth was performed using the above apparatus. Ga on the substrate
H ₂ was used for As and gas.

The GaAs substrate was housed in the surface treatment chamber and evacuated to 10 ^-6 mb. Then, H ₂ was flowed at 50 sccm through the nozzle. This H ₂ was irradiated with ultraviolet light from an Ar-F excimer laser to generate hydrogen radicals.

In this state, while rotating the GaAs substrate as described above, the surface of the substrate was subjected to a cleaning treatment by exposing the substrate surface to a gas containing radicals at about 250 ° C. for about 20 minutes.

Next, the GaAs substrate was moved to the growth chamber by following the procedure described above, and AlGaAs was heteroepitaxially grown on the treated substrate surface according to the usual procedure.

After that, an MIS structure was formed on the substrate and the CV characteristics thereof were measured to determine the interface state density. As a result, the interface state density of the sample epitaxially grown after the surface treatment was -10 ¹¹ cm ^-2 · eV ^-1 . On the other hand, the interface state density of the sample that was heteroepitaxially grown without surface treatment was -10 ¹² cm ^-2 · e.
It was V ^-1 . From this result, it was clarified that the surface state density using the hydrogen radical by photoexcitation reduces the interface state density by about one digit.

Example 2 GaAs was used as the substrate and AsH ₃ was used as the gas, and MBE growth was performed in the above apparatus.

The GaAs substrate was housed in the surface treatment chamber and evacuated to 10 ^-6 mb.
₃ was flowed at 10 sccm. This AsH ₃ was irradiated with ultraviolet light from an Ar-F excimer laser to generate radicals. As described above, while rotating the GaAs substrate, the surface of the substrate was exposed to a gas containing radicals at about 250 ° C. for about 20 minutes to clean the surface.

Next, following the procedure described above, the GaAs substrate is moved to the growth chamber, and AlGaA is formed on the treated substrate surface.
s was heteroepitaxially grown.

After that, an MIS structure was formed on the substrate and the CV characteristics thereof were measured to determine the interface state density. As a result, the interface state density of the sample epitaxially grown after the surface treatment was -10 ¹¹ cm ^-2 · eV ^-1 . On the other hand, the interface state density of the sample that was heteroepitaxially grown without surface treatment was -10 ¹² cm ^-2 · e.
It was V ^-1 . From this result, it was clarified that the surface state density using the hydrogen radical by photoexcitation reduces the interface state density by about one digit.

Example 3 InP was used as the substrate and H ₂ was used as the gas.
BE growth was performed.

The InP substrate was housed in the surface treatment chamber and evacuated to 10 ^-6 mb, and then H ₂ was flown at 50 sccm through the nozzle. This H ₂ was irradiated with ultraviolet light from an Ar-F excimer laser to generate hydrogen radicals.

While rotating the InP substrate as described above, the substrate surface was exposed to a gas containing hydrogen radicals at about 250 ° C. for about 20 minutes to clean the surface.

Next, following the procedure described above, the InP substrate is moved to the growth chamber, and GaInAs is formed on the surface of the processed substrate.
Was heteroepitaxially grown.

Then, the characteristics of the epitaxial growth layer were evaluated by hole measurement. As a result, the carrier mobility of the sample epitaxially grown after the surface treatment was ˜11000 cm ² / V · s. On the other hand, the carrier mobility of the sample that was heteroepitaxially grown without surface treatment was about 5000 cm ² / V · s.
From this result, it was clarified that the carrier mobility increased more than twice by the surface treatment using the hydrogen radical by photoexcitation.

Example 4 InP was used as the substrate, and PH ₃ was used as the gas.
BE growth was performed.

The InP substrate is housed in the surface treatment chamber,
After exhausting to 10 ^-6 mb, PH ₃ was added to 1 through the nozzle.
Flowed at 0 sccm. This PH ₃ was irradiated with ultraviolet light from an Ar-F excimer laser to generate radicals.

While rotating the InP substrate as described above, the substrate surface was exposed to a gas containing radicals at about 250 ° C. for about 20 minutes to clean the surface.

Next, the InP substrate is moved to the growth chamber by following the procedure described above, and GaInAs is formed on the surface of the treated substrate.
Was heteroepitaxially grown.

The characteristics of the epitaxial growth layer were evaluated by hole measurement. As a result, the carrier mobility of the sample epitaxially grown after the surface treatment was ˜12000 cm ² / V · s. On the other hand, the carrier mobility of the sample that was heteroepitaxially grown without surface treatment was about 5000 cm ² / V · s.
From this result, it was clarified that the carrier mobility increased more than twice by the surface treatment using radicals by photoexcitation.

[0058]

As described above, in the present invention, the radicals generated by photoexcitation are used for cleaning the substrate surface. Therefore, the substrate surface can be effectively cleaned at a lower temperature than before without damaging the substrate. You can

Further, according to the present invention, after the substrate surface is cleaned, the epitaxial growth is continuously performed in a vacuum. Therefore, the interface state density can be suppressed to be low and the epitaxial growth can be performed.

Therefore, it is very effective to apply the present invention to epitaxial growth on a III-V compound semiconductor substrate having a high surface state density.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a specific example of an apparatus according to the present invention.

[Explanation of symbols]

 1 Gas Supply System 2 Excimer Laser 3 Viewport 4 Susceptor 5 Surface Treatment Chamber 6a, 6b Gate Valve 7 Preparation Room 8 Growth Chamber 9a, 9b, 9c Ultra High Vacuum Pump 10 Molecular Beam Epitaxial Growth Equipment 11a, 11b Transfer Chamber 12 Substrate

Claims (2)

[Claims] 1. The surface of a III-V group compound semiconductor substrate held in vacuum is treated with a gas in which radicals are generated by light irradiation using at least one of hydrogen and a hydrogen compound of the group V element. And a step of irradiating the treated substrate surface with a molecular beam to form an epitaxial layer while maintaining a vacuum state,
Molecular beam epitaxy. 2. An apparatus for irradiating a substrate with a molecular beam to form an epitaxial layer on the substrate, wherein the substrate is housed and the surface of the substrate is exposed to radicals generated by light irradiation. A reaction chamber, a first exhaust system for exhausting the reaction chamber, a gas supply means for supplying a gas for radical formation to the reaction chamber, and a gas supply for optically exciting molecules in the gas Means for irradiating the gas supplied from the means to the reaction chamber with light, a growth chamber for accommodating the substrate processed in the reaction chamber and performing molecular beam epitaxial growth, and for exhausting the growth chamber Molecular beam epitaxy, including a second exhaust system of No. 2, and a transfer chamber for connecting the reaction chamber and the growth chamber while maintaining a vacuum state and transferring the substrate from the reaction chamber to the growth chamber. Le growth apparatus.