JPH04214616A - Compound semiconductor crystal growth method and device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor crystal growth method and a growth apparatus, and more particularly to a molecular beam epitaxial growth method and a growth apparatus for epitaxially growing a semiconductor crystal on a compound semiconductor substrate. Molecular beam epitaxial growth, in which an epitaxial layer is grown by heating a compound semiconductor substrate to an appropriate temperature in a vacuum and irradiating the substrate with semiconductor elements in the form of molecular beams.
MBE) method is capable of growing ultra-thin films with good controllability,
Due to the good steepness of the interface in the heteroepitaxial structure, it is attracting attention as a crystal growth technique for manufacturing electronic devices and optical devices using compound semiconductors, as well as OE devices equipped with both.

[0002] When manufacturing this composite device, it is necessary to grow an epitaxial layer again on the substrate on which some devices have been formed by previous processing, but in this case, it is necessary to grow the epitaxial layer with good quality and It is important not to damage the previously formed device.

0003

2. Description of the Related Art When growing a semiconductor epitaxial layer on a compound semiconductor substrate by MBE, it is necessary to clean the compound semiconductor substrate prior to crystal growth in order to make the epitaxial layer of good quality. Conventional methods for cleaning compound semiconductor substrates include the following.

(1) A thermal cleaning method in which the substrate is heated in vacuum immediately before crystal growth to remove the natural oxide film (about 1 nm thick). (2) For example, “MBE-Ga by thermal etching”
As substrate pretreatment effect, Japan Journal o
f Applied Physics, Vol. 25,
1986, pp. 1216-1220'', etc.

(3) For example, “M by thermal oxide film formation and removal”
Cleaning of BE-GaAs substrate, Journal of
Applied Physics, Vol. 63,19
88, p. 404" and the like. (4) For example, “MBE by mixing HCl gas and H2
In-situ cleaning of GaAs substrates, Journal of
Applied Physics, Vol. 95,19
89, pp. 322-327''.

However, all of these methods require heating the substrate to a temperature higher than the temperature at which crystal growth is possible. For example, if we take a GaAs substrate as an example,
While the temperature at which crystal growth is possible is around 500°C, (
Heating to a substrate temperature of 580 to 600°C or higher in method 1), 750°C or higher in method (2), 600 to 640°C or higher in method (3), and 450 to 500°C or higher in method (4) is necessary.

However, according to the invention of the present inventor,
Patent application No. 177768, filed on July 15, 1983,
JP-A-2-26892 discloses a method of etching and cleaning at a lower substrate temperature than the above method (
5) was disclosed. This substrate cleaning method (5) irradiates the surface of a compound semiconductor substrate with ultraviolet rays to promote the decomposition of the reactive gas and the reaction between the substrate surface and the reactive gas, thereby performing etching and cleaning even at low substrate temperatures. This makes cleaning possible.

[0008]

[Problems to be Solved by the Invention] The methods (1) to (3) above heat the substrate to a temperature higher than the crystal growth temperature as described above, so that the crystal growth occurs on the substrate on which the device is formed. If regrowth is performed, there is a problem in that it adversely affects the characteristics of the device and deteriorates the characteristics.

Furthermore, it is known that in crystal growth following heat treatment by method (1), a carrier depletion layer is generated at the growth interface, making it difficult to obtain a good quality epitaxial layer. It is believed that this carrier depletion layer is generated because impurities remaining on the substrate after heat treatment, particularly residual carbon, serve as acceptors. Methods (2) and (3) can remove the residual carbon by increasing the degree of treatment, but in that case, the surface morphology is significantly deteriorated. For this reason,
The degree of treatment must be kept to a level that does not deteriorate the surface morphology, and a certain amount of residual carbon will remain after the treatment. In the growth subsequent to this treatment, although it is improved over the method (1), the carrier depletion layer described above is generated, making it difficult to obtain a good quality epitaxial layer.

[0010] Method (4) heats the substrate to a temperature lower than that in methods (2) and (3), so
The substrate can be cleaned without degrading the surface morphology. However, when crystals are regrown on a substrate on which devices have already been formed, further lowering the substrate temperature becomes an important issue. Method (5) solves the problem in method (4),
This makes it possible to lower the substrate temperature. However, controlling the etching depth depends on the flow rate of reactive gas, the degree of vacuum, or the irradiation time of ultraviolet rays, and these controls are difficult. Therefore, it is difficult to say that it is desirable for precise etching processing that targets the surface of a substrate on which a device is formed.

An object of the present invention is to perform MBE for growing a semiconductor epitaxial layer on a compound semiconductor substrate.
It is possible to clean the substrate before crystal growth without degrading the surface morphology of the substrate surface even if the heating temperature of the compound semiconductor substrate is low, and also to create a high-quality epitaxial layer that reduces the carrier depletion layer that occurs at the crystal growth interface. An object of the present invention is to provide a compound semiconductor crystal growth method and a growth apparatus thereof, which can form a compound semiconductor crystal and digitally control the etching depth on the order of atomic layers.

0012

[Means for Solving the Problems] The above object is to provide a compound semiconductor crystal growth method using a molecular beam epitaxial growth method in which a compound semiconductor crystal is epitaxially grown on a compound semiconductor substrate, in which the compound semiconductor substrate before crystal growth is grown under reduced pressure. a first step of holding and heating to remove moisture adsorbed on the surface of the compound semiconductor substrate; and a second step of continuously irradiating the compound semiconductor substrate with ultraviolet rays while exposing the compound semiconductor substrate to a reactive gas atmosphere. This is achieved by a method for growing compound semiconductor crystals, which includes the steps of step 2 and cleaning the surface of the compound semiconductor substrate before crystal growth.

[0013] The above object also provides a compound semiconductor crystal growth apparatus having a crystal growth chamber for growing a compound semiconductor crystal on a compound semiconductor substrate using a molecular beam epitaxial growth method. a substrate manipulator capable of maintaining the substrate temperature of a semiconductor substrate at a desired temperature; an ultraviolet lamp disposed opposite to the compound semiconductor substrate held by the substrate manipulator and irradiating the surface of the compound semiconductor substrate with ultraviolet rays; and the ultraviolet lamp. and a shutter provided between the compound semiconductor substrate and controlling the time of ultraviolet irradiation of the surface of the compound semiconductor substrate by the ultraviolet lamp,
A compound semiconductor substrate pre-treatment chamber is provided in communication with the crystal growth chamber via a gate valve, and is capable of supplying reactive gas and hydrogen gas, and is capable of applying reduced pressure. This is achieved by a compound semiconductor crystal growth apparatus characterized by cleaning.

[0014]

[Operation] According to the present invention, in MBE for growing an epitaxial layer of a semiconductor on a compound semiconductor substrate, the heating temperature of the compound semiconductor substrate can be lowered, and the substrate can be cleaned before crystal growth without deteriorating the surface morphology of the substrate surface. realizable. Furthermore, it is possible to form a high-quality epitaxial layer with a reduced carrier depletion layer generated at the crystal growth interface, and it is also possible to digitally control the etching depth on the order of atomic layers.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method and apparatus for growing a compound semiconductor crystal according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram for explaining a compound semiconductor crystal growth method according to a first embodiment of the present invention, and FIG. 2 is a block diagram of a compound semiconductor crystal growth apparatus according to the first embodiment of the present invention.

In this example, the reactive gas is irradiated onto the substrate to be adsorbed, and after exhausting the reactive gas remaining in the atmosphere, the substrate is irradiated with ultraviolet rays to separate the adsorbed reactive gas from the substrate. By periodically repeating the steps of reactive gas irradiation, exhaust, and ultraviolet ray irradiation, the desired depth of etching can be achieved depending on the number of repetitions. It is characterized by being able to perform the following.

In this embodiment, the compound semiconductor substrate 18 is
i-doped n-type GaAs was used, and hydrogen chloride (HCl) gas was used as the reactive gas. FIG. 1 shows the process sequence of introducing, stopping, and exhausting reactive gas, and irradiating and stopping ultraviolet rays in this example. The GaAs substrate 18 is mounted on a molybdenum (Mo) block 19 for substrate mounting in the atmosphere.
The substrate is bonded to the substrate using indium (In) solder, introduced into the substrate exchange chamber 34 through the substrate entrance/exit of the growth apparatus, and evacuated to a high vacuum. Recently, so-called I
An n-free holder has also been developed, and this can be used to
Introduce the As substrate 18 into the substrate exchange chamber 34 in the same manner as above,
High vacuum evacuation is often performed. Especially GaA
This In free holder is used when a device is formed on the epitaxial layer on the s-substrate 18 and then epitaxial growth is performed thereon again.

The temperature inside the board exchange room 34 is 1E-7 Torr to 1
After exhausting to about E-9 Torr, a gate valve (not shown) is opened and the GaAs substrate 18 is transferred to the dry etching chamber (substrate pretreatment chamber) 10 through the substrate transfer chamber 32, and is mounted on the substrate manipulator 14. , close the gate valve between the vacuum chambers. A substrate heater 16 provided within the substrate manipulator 14 can heat the GaAs substrate 18 to a maximum of 800°C. The dry etching chamber 10 is preliminarily heated to 1E-7 to 1 by the action of a turbo molecular pump.
It is evacuated to a vacuum of about E-9 Torr. The substrate manipulator 14 moves the substrate up and down and the direction from 0 to 200.
° Can be changed. A viewing port (not shown) made of synthetic quartz was provided at the substrate transfer lot 12 and the reaction side port, so that ultraviolet rays could be irradiated into the dry etching chamber 10 by a low-pressure mercury lamp 22 installed on the atmosphere side. If a low-pressure mercury lamp 22 is used as a light source, as shown in the emission wavelength characteristic diagram of FIG.
Ultraviolet light of nm and 185 nm can be easily obtained. If this wavelength is converted into energy, it is approximately 4.9 eV from the equation E=hν.
and approximately 6.7 eV. This energy is, for example, GaA
The reaction dissociation energy between the s-substrate 18 and HCl gas (approximately 1.
3 eV). Therefore, the reaction between the reactive gas adsorbed on the substrate and the substrate can occur at low temperature.

A shutter 20 is provided between the low-pressure mercury lamp 22 and the quartz viewport glass for mechanically opening and closing irradiation of the dry etching chamber 10 with ultraviolet rays. Ultraviolet light is absorbed by oxygen in the atmosphere. In order to effectively use the ultraviolet light emitted from the low-pressure mercury lamp 22, the space between the low-pressure mercury lamp 22 and the quartz viewport glass is sealed, and the atmosphere inside is replaced with dry nitrogen gas. Further, a hydrogen chloride cylinder and a hydrogen cylinder 24 are connected to the dry etching chamber 10 via a valve 28 and a mass flow controller 26, and each mass flow controller 26 is used to control hydrogen chloride gas (H2O gas) at a constant flow rate.
Cl gas) and hydrogen can be introduced. By adjusting the flow rate, the degree of vacuum within the dry etching chamber 10 can be controlled. The degree of vacuum in the dry etching chamber 10 can also be achieved by keeping the gas flow rate constant and adjusting the conductance of the exhaust system. Gas line valve 2
Gas dry etching chamber 1 by opening and closing 8
Introducing and stopping into 0 can be controlled. Further, each gas line is provided with a vent line 30, and by switching the valve 28, gas can be introduced into the dry etching chamber 10 or vented to the exhaust line.

The surface of the GaAs substrate 18 is placed parallel to the quartz viewport glass and directed toward the ultraviolet lamp 22.
Open the HCl gas valve 28 and supply HCl gas at a flow rate of 50
SCCM is introduced into the dry etching chamber 10. At this time, the substrate temperature of the GaAs substrate 18 remains at room temperature. The degree of vacuum in the dry etching chamber 10 is set to 0.1 to 1 Torr.
After 1 minute, the valve 28 of the HCl gas line is closed to stop the flow of HCl gas. After continuing to exhaust the HCl gas for 3 minutes, the shutter 20 in front of the ultraviolet lamp 22 is opened to irradiate the surface of the GaAs substrate 18 with ultraviolet rays. The ultraviolet lamp 22 is lit in advance and shut off by a mechanical shutter until the time of irradiation. G
After continuing to irradiate the aAs substrate 18 with ultraviolet light for 2 minutes, the shutter 20 is closed to stop the ultraviolet irradiation. or more HCl
The steps of gas introduction, stop, exhaust, ultraviolet irradiation, and stop are considered as one cycle, and this process is repeated 20 times.

Following the above steps, after the degree of vacuum in the dry etching chamber 10 reaches 1E-8 to 1E-9 Torr, the gate valve is opened and the GaAs substrate 18 is transferred to the substrate transfer chamber evacuated to a high vacuum. 32 to the MBE growth chamber 38. A substrate manipulator (not shown) incorporating a substrate heater (not shown) in the MBE growth chamber 38
Attach and hold it.

In the MBE growth chamber 38, arsenic (A
s4) While irradiating As4 molecular beam from a molecular beam source,
Heating the GaAs substrate 18 to a temperature of about 600°C,
The GaAs layer is epitaxially grown while maintaining this temperature. At this time, S
i is doped to the same concentration as the GaAs substrate 18, about 7E16 cm-3. In addition, the growth rate in this case is 1 μm/
h, the growth layer thickness is 0.5 μm.

FIG. 4 is a diagram showing the carrier concentration profile near the interface between the GaAs substrate 18 and the epitaxially grown GaAs layer. In the figure, the horizontal axis shows Ga
The depth from the surface of the As layer is plotted, and the vertical axis plots the carrier concentration, and the solid line is a characteristic line related to this example. Moreover, the broken line is a characteristic line related to the conventional example (1), and these data are obtained by the CV measurement method. The samples used were one that had been pretreated according to this example, and one that had been thermally cleaned by holding the substrate temperature at 600° C. for 10 minutes in a growth chamber under As beam irradiation as a conventional example.

As can be seen from the figure, in the case of this embodiment, the carrier concentration is uniform from the epitaxial layer to the substrate side, and there is no carrier depletion region, whereas in the case of the conventional technique, there is no clear depletion region. This is thought to be due to impurities such as carbon remaining on the substrate surface. From these results, it can be seen that in this example, contaminants were successfully removed from the substrate surface, and no crystal defects were introduced.

In this example, the steps of introducing HCl gas, stopping it, exhausting it, and irradiating it with ultraviolet rays and stopping it were repeated 20 times, and the surface of the GaAs substrate 18 was etched by about 6 nm by this pretreatment. This means that one atomic layer's worth of etching is performed in one cycle of the process. The surface morphology after etching was good, and a mirror surface similar to that before etching was obtained. Since the depth of etching can be determined by the number of repetitions of this process cycle, pretreatment can be performed accurately, with good stability and reproducibility.

In this embodiment, the GaAs substrate 18 held by the substrate manipulator 14 in the dry etching chamber 10 is digitally etched at room temperature through the steps of HCl gas irradiation/stop/exhaust and ultraviolet irradiation/stop. However, it is also possible to heat and hold the GaAs substrate 18 using the substrate heater 16 in the substrate manipulator 14 and perform etching in the same manner. In this case, in the case of the GaAs substrate 18, reaction and decomposition with HCl gas occur at a substrate temperature of 400°C or higher, so if the substrate is heated to a temperature higher than this, the effect of this example cannot be obtained and etching can be performed without UV irradiation. proceed. Therefore, the substrate heating is 4
The temperature must be below 00°C.

A compound semiconductor crystal growth method according to a second embodiment of the present invention will be explained with reference to FIG. Similar to the case shown in the first embodiment, the compound semiconductor substrate 18 is made of Si-doped n-type GaAs, and the reactive gas is hydrogen chloride (HC).
l) This is a case in which gas is used, but hydrogen gas is further introduced during the pretreatment step. FIG. 5 shows the process sequence of substrate temperature control, hydrogen gas introduction/stopping, reactive gas introduction/stopping/exhaust, and ultraviolet irradiation/stopping in this embodiment.

The GaAs substrate 18 is etched in the dry etching chamber 1.
0 and holding by the substrate manipulator 14 is the same as in the first embodiment. Thereafter, the substrate is heated using the substrate heater 16 built into the substrate manipulator 14. At this time, the hydrogen gas line valve 28
Open the tank and continue evacuation by flowing hydrogen gas at a flow rate of 50 sccm. By keeping the gate valve fully open to maximize the conductance of the exhaust line, the degree of vacuum can be reduced to 1.
It is held on an E-3 Torr stand. In this hydrogen atmosphere, G
The aAs substrate 18 is heated to 300° C. and held for about 10 minutes. Through this step, moisture adsorbed on the surface of the GaAs substrate 18 is removed. By continuing to flow hydrogen gas, the moisture released from the surface of the GaAs substrate 18 can be exhausted without being adsorbed to the wall surface inside the dry etching chamber 10.

The temperature of the GaAs substrate 18 is lowered to 200° C. and an etching process begins. The GaAs substrate 18 is placed parallel to the quartz viewport glass and toward the ultraviolet lamp 22 . Open the valve 28 of the HCl gas line and supply HCl gas to the dry etching chamber 1 at a flow rate of 50 sccm.
Introduce to 0. The degree of vacuum in the dry etching chamber 10 is set to 0.
．． Maintain at 5 Torr. At this time, the pressure in the dry etching chamber 10 is 0.5 Torr due to HCl gas and hydrogen. After 1 minute, the HCl gas line valve 28 is closed to stop the flow of HCl gas. Hydrogen gas continues to flow. As the hydrogen gas continues to flow, HCl gas is replaced and exhausted quickly, so the exhaust time ends in about 10 seconds. Thereafter, the shutter 20 in front of the ultraviolet lamp 22 that has been turned on in advance is opened to irradiate the GaAs substrate 18 with ultraviolet rays. GaAs substrate 18
UV irradiation continues for 1 minute. After that, shutter 20
Close the door to stop UV irradiation. Introducing more HCl gas
This process is repeated 10 times, with the steps of stopping, exhausting, and stopping ultraviolet irradiation as one cycle.

[0030] Following the above steps, the substrate heating heater 16
The input power is turned off, the substrate temperature is lowered from 200° C., the introduction of hydrogen gas is stopped, and the degree of vacuum in the dry etching chamber 10 is evacuated to 1E-8 Torr. Thereafter, the gate valve is opened and the GaAs substrate 18 is transferred to the MBE growth chamber 38 through the substrate transfer chamber 32 which is evacuated to a high vacuum. It is mounted and held on a substrate manipulator that has a built-in substrate heater in the MBE growth chamber 38.

In the MBE growth chamber 38, arsenic (A
s4) While irradiating As4 molecular beam from a molecular beam source,
Heating the GaAs substrate 18 to a temperature of about 600°C,
The GaAs layer is epitaxially grown while maintaining this temperature. At this time, S
i is doped to the same concentration as the GaAs substrate 18, about 7E16 cm-3. In addition, the growth rate in this case is 1 μm/
h, the growth layer thickness is 0.5 μm.

GaAs substrate 18 and epitaxial growth G
The carrier concentration profile near the interface of the aAs layer is similar to the result of the first example (FIG. 4). According to this embodiment, HCl gas introduction/stop/exhaust, ultraviolet irradiation/
The time required for the shutdown process can be shortened by continuously introducing hydrogen gas. Furthermore, the introduction of hydrogen gas has the effect of coating the etched surface with hydrogen molecules during the reaction between the surface of the GaAs substrate 18 during ultraviolet irradiation and HCl gas adsorbed molecules, thereby stabilizing the etched surface. As a result, deterioration of the surface morphology of the GaAs substrate 18 after etching can be suppressed, and a mirror surface can be obtained even in deep etching.

In this embodiment, the etching step was carried out while maintaining the substrate temperature at 200° C., but after the step of removing moisture from the surface of the GaAs substrate 18, the substrate temperature was lowered from room temperature to 400° C.
Similarly, etching can be performed digitally by holding the film at a temperature up to 10°C. In this embodiment, the GaAs substrate 1
8 In the process of removing moisture from the surface, the substrate temperature is heated in a hydrogen gas atmosphere and held at 300°C for 10 minutes. Another method is to irradiate the substrate surface with ultraviolet light while keeping the substrate temperature at room temperature. This is a method in which molecules adsorbed on the surface of the GaAs substrate 18 are decomposed and released using ultraviolet energy. With this method, the moisture removal process can be easily completed in a shorter time than when heating the substrate. In the case of the GaAs substrate 18, approximately 10 minutes of ultraviolet irradiation time is sufficient.

A method for growing compound semiconductor crystals according to a third embodiment of the present invention will be explained. In this example, n
A case where a + type GaAs layer is grown as an ohmic contact layer will be described. It is possible to form an active layer on the GaAs substrate 18 using ion implantation, process a part of it, grow an epitaxial layer, and form a new active layer to fabricate a composite device such as an FET and a laser. often done. Alternatively, if a low carrier concentration or insulating layer is required directly under the gate electrode of the FET, while a high concentration carrier layer is required for the source and drain electrodes for ohmic contact, an insulating layer may be used. After the second growth, only the ohmic electrode region is removed by processing, and an n+ type GaAs layer is sometimes formed as an ohmic contact layer with the active layer surface as the substrate surface.

FIG. 6 shows a cross-sectional view of the substrate for explaining this embodiment. A non-doped GaAs buffer layer 52 is formed on a semi-insulating GaAs substrate 51, and a Si-doped GaAs active layer 53 is formed on top of the non-doped GaAs buffer layer 52. S
Non-doped GaAs is formed on the i-doped GaAs active layer 53.
A layer 54 is formed. Each of them is formed by epitaxial growth ((a) in the same figure).

A gate electrode 61 is formed on the non-doped GaAs layer 54, and a silicon oxide film 71 is coated on top of the gate electrode 61.
Using this as a mask, the non-doped GaAs layer 54 is etched to form source/drain regions leaving approximately 1 nm of the non-doped GaAs layer 54 (FIG. 4(b)). The GaAs substrate 18 shown in FIG. 4B is held on the substrate mounting block 19 using an indium free holder, introduced into the substrate exchange chamber 34, and subjected to high vacuum evacuation.

The inside of the board exchange room 34 is from 1E-7 to 1E-9.
After exhausting to about Torr, open the gate valve and turn to G.
The aAs substrate 18 is transferred to the dry etching chamber 10 through the substrate transfer chamber 32, and transferred to the substrate manipulator 1.
4, the gate valve between the substrate transfer chambers 32 is closed. The GaAs substrate 18 is kept at room temperature. The substrate surface is quartz viewport glass, that is, ultraviolet lamp 2
Install it so that it faces parallel to 2.

[0038] Open the valve 28 of the hydrogen gas line, let hydrogen gas flow in at a rate of 50 sccm, and continue exhausting. By keeping the gate valve fully open to maximize the conductance of the exhaust line, the degree of vacuum is 1E-3 Torr.
It is held at r level. In this hydrogen gas atmosphere, the substrate surface is irradiated with ultraviolet rays to desorb the adsorbed molecules. HCl
Open the gas line valve 28 and supply HCl gas at a flow rate of 5.
It is introduced into the dry etching chamber 10 at 0 sccm. The degree of vacuum in the dry etching chamber 10 is maintained at 0.5 Torr. At this time, the pressure in the dry etching chamber 10 is 0.5 Torr due to HCl gas and hydrogen. After 1 minute, close the valve 28 of the HCl gas line and turn off the HCl gas line.
Stop the flow of Cl gas. Hydrogen gas continues to flow. Since HCl gas is replaced and exhausted quickly, the exhaust time is completed in about 10 seconds. After that, open the shutter 20 in front of the ultraviolet lamp 22 that was lit in advance,
The GaAs substrate 18 is irradiated with ultraviolet light. GaAs substrate 1
The UV irradiation to 8 continues for 1 minute. Then shutter 2
Close 0 to stop UV irradiation. The above steps of introducing HCl gas, stopping, exhausting, and stopping ultraviolet irradiation are considered as one cycle.
Repeat this 5 times.

After the above steps, the introduction of hydrogen gas is stopped, and the degree of vacuum in the dry etching chamber 10 is reduced to 1E-8 Torr.
Exhaust to r level. Then open the gate valve and
A substrate transfer chamber 32 in which the GaAs substrate 18 is evacuated to a high vacuum
and transferred to the MBE growth chamber 38. MBE growth room 38
Attach and hold the board to the board manipulator that has a built-in board heater.

In the MBE growth chamber 38, GaAs is processed while being irradiated with an As molecular beam from an As molecular beam source.
The substrate 18 is heated to a temperature of about 500 DEG C., and while maintaining this temperature, a GaAs layer 55 doped with Sn to about 2E19 to 5E19 cm@-3 from an Sn molecular beam source instead of Si is epitaxially grown. In this case, the growth rate was 1 μm/h, and the growth layer thickness was 0.5 μm/h.
It is 3 μm.

By this regrowth, a GaAs layer 55 is formed on the silicon oxide film 71, but since the base is silicon oxide, this does not become an epitaxial layer but a polycrystalline film, so the silicon oxide is etched. It can be easily removed by removing it. High concentration GaA in the source/drain region grown in this way
By forming a source electrode 62 and a drain electrode 63 on the s-layer 55, a non-alloy ohmic electrode can be made (FIG. 4(c)).

In this example, a very thin layer of about 1 nm on the processed substrate can be precisely removed, and residual impurities such as carbon on the crystal surface that adhered during processing can be removed, so non-alloy It became possible to form ohmic electrodes.

[0043]

According to the present invention, when a compound semiconductor crystal layer is epitaxially grown on a compound semiconductor crystal substrate, in a dry etching chamber, the surface of the compound semiconductor crystal substrate is irradiated with a reactive gas, stopped, exhausted, ultraviolet irradiation,
A stopping process is performed to etch the surface layer of the substrate and simultaneously remove contaminants such as carbon.

By adopting this configuration, the substrate surface and processed surface layer can be removed in atomic layer units with good control, and impurities such as carbon attached to the surface can be reliably removed. A thin epitaxial crystal layer with good physical properties can be grown, and a semiconductor device with good properties can be easily manufactured.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a compound semiconductor crystal growth method according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a compound semiconductor crystal growth apparatus according to a first embodiment of the present invention.

FIG. 3 is a diagram of emission wavelength characteristics of a low-pressure mercury lamp.

FIG. 4: GaAs substrate and epitaxially grown GaAs
FIG. 3 is a diagram showing a carrier concentration profile near the interface of layers.

FIG. 5 is an explanatory diagram of a compound semiconductor crystal growth method according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram of a cross section of a substrate according to a third embodiment of the present invention.

[Explanation of symbols]

10... Dry etching chamber 12... Substrate transfer rod 14... Substrate manipulator 16... Substrate heater 18... Compound semiconductor substrate (GaAs substrate) 19... Substrate mounting block 20... Shutter 22... Ultraviolet lamp (low pressure mercury lamp) 24... Gas cylinder 26... Mass flow controller 28...Valve 30...Vent line 32...Substrate transfer chamber 34...Substrate exchange chamber 36...Substrate transfer rod 38...MBE growth chamber 51...Semi-insulating GaAs substrate 52...Non-doped GaAs buffer layer 53...Si-doped GaAs active layer 54 ...Non-doped GaAs layer 55...Si-doped GaAs ohmic contact layer 61
...Al gate electrode 62...AuGe source electrode 63...AuGe drain electrode 71...silicon oxide film

Claims (7)

[Claims] 1. In a compound semiconductor crystal growth method using a molecular beam epitaxial growth method for epitaxially growing a compound semiconductor crystal on a compound semiconductor substrate, the compound semiconductor substrate before crystal growth is held under reduced pressure and heated, and the compound semiconductor crystal is a first step of removing moisture adsorbed on the surface of the semiconductor substrate, and a second step of continuously irradiating the compound semiconductor substrate with ultraviolet rays while exposing the compound semiconductor substrate to a reactive gas atmosphere, A compound semiconductor crystal growth method characterized by cleaning the surface of the compound semiconductor substrate before crystal growth. 2. A compound semiconductor crystal growth method using a molecular beam epitaxial growth method in which a compound semiconductor crystal is epitaxially grown on a compound semiconductor substrate, wherein the surface of the compound semiconductor substrate is heated by irradiating hydrogen on the surface of the compound semiconductor substrate. a first step of removing moisture adsorbed on the surface of the substrate; a second step of irradiating the surface of the compound semiconductor substrate with a reactive gas; a third step of exhausting the reactive gas; and a third step of evacuating the compound semiconductor substrate. and a fourth step of irradiating the surface with ultraviolet rays, and by repeating the second step to the fourth step multiple times in this order as one cycle, the surface of the compound semiconductor substrate before crystal growth is etched. A compound semiconductor crystal growth method characterized by: 3. The compound semiconductor crystal growth method according to claim 1 or 2, wherein hydrogen gas is continuously introduced throughout the entire process. 4. The compound semiconductor crystal growth method according to claim 1, in which, instead of the first step, the compound semiconductor substrate before crystal growth is held under reduced pressure and irradiated with ultraviolet rays. A method for growing a compound semiconductor crystal, comprising a step of removing moisture adsorbed on the surface. 5. The compound semiconductor crystal growth method according to claim 2, in which, instead of the first step, the compound semiconductor substrate before crystal growth is held under reduced pressure and irradiated with ultraviolet rays. A method for growing a compound semiconductor crystal, comprising a step of removing moisture adsorbed on the surface. 6. The compound semiconductor crystal growth method according to claim 1, wherein the compound semiconductor substrate is made of GaAs.
a substrate, wherein the reactive gas is hydrogen chloride gas;
A compound semiconductor crystal growth method characterized in that the heating temperature of the compound semiconductor substrate is 400° C. or less. 7. A compound semiconductor crystal growth apparatus having a crystal growth chamber for growing a compound semiconductor crystal on a compound semiconductor substrate using a molecular beam epitaxial growth method, wherein the compound semiconductor substrate is held and the substrate of the compound semiconductor substrate is grown. a substrate manipulator capable of maintaining a temperature at a desired temperature; an ultraviolet lamp disposed opposite to the compound semiconductor substrate held by the substrate manipulator and irradiating the surface of the compound semiconductor substrate with ultraviolet rays; and the ultraviolet lamp and the compound semiconductor. a shutter provided between the substrates for time-controlling ultraviolet irradiation of the surface of the compound semiconductor substrate by the ultraviolet lamp; provided in communication with the crystal growth chamber via a gate valve; A compound semiconductor crystal growth apparatus comprising a compound semiconductor substrate pretreatment chamber capable of supplying hydrogen gas and applying reduced pressure, and cleaning the surface of the compound semiconductor substrate before crystal growth.