JPH0758688B2 - Method for forming compound semiconductor thin film - Google Patents

Description

The present invention relates to a method for forming a compound semiconductor thin film. More specifically, it relates to a novel method for forming a compound semiconductor thin film using epitaxial growth of crystals.

2. Description of the Related Art Compound semiconductors are attracting attention as the most suitable ones for the recent trend of semiconductor devices such as ultra-high speed and high functionality.

In addition, there are some compound semiconductors that can artificially form various semiconductor mixed crystals while maintaining the zinc blende type crystal structure, and a heterojunction that can form a lattice match between different semiconductor crystals is formed. Can be realized. Therefore, using this, an ultrafast electronic device utilizing modulation doping,
Various optical devices such as LDs have been developed.
In recent years, research and development of new devices that utilize the new physical properties of superlattice structures, especially compound semiconductor devices such as lasers and HEMTs, have made rapid progress.

These devices are composed of a substrate and a thin film having a large number of layers having a complicated composition laminated on the substrate. It is known that the performance of this type of device is greatly influenced by the structure in the thin film, especially the steepness of the doping profile between adjacent layers. Therefore, important issues in forming a superlattice structure are the controllability of the thickness of the grown thin film, the steep doping profile at the interface, and the reduction of crystal defects. In order to solve these problems, the technique of forming compound semiconductor thin films such as GaAs and AlGaAs by epitaxial growth is being used in large-area GaAs / AlGaAs solar cells, high-performance field effect transistors, their LSIs and / or semiconductor lasers, EOICs, etc. Research is continuing as to what can be manufactured at low cost.

Problems to be Solved by the Invention Conventional methods for forming a compound semiconductor thin film on a substrate include a metal organic thermal decomposition growth method (hereinafter referred to as MOCVD) and a molecular beam epitaxy method (hereinafter referred to as MBE). Has been.

The metalorganic pyrolysis vapor deposition method is, for example, Etch. M. Papers such as HM Manasevit [Journal
Of Electrochemical Society (J. Electr
ochem.Soc.), 1973 120, 569]. This method is a method of transporting an organometallic compound and a hydride carrier gas onto a heated substrate, and forming a compound semiconductor thin film on the substrate by thermal decomposition.

However, in the metalorganic decomposition vapor deposition, since the raw material molecules diffuse in the velocity boundary layer formed on the surface of the substrate and the growth proceeds, the in-plane non-uniformity of the thickness of the velocity boundary layer is caused by the growth film thickness of the substrate. It was virtually impossible to maintain the controllability of the monoatomic layer over a wide area in the plane of the substrate, leading to in-plane non-uniformity.

On the other hand, the molecular beam epitaxy method (hereinafter, MBE) is, for example,
Elle. Elle. As published in Journal of Vacuum Science Technology (J.Vac.Sci.Technol.), 1973,10-5,11 by L. Chang et al., The raw material elements evaporated in a high vacuum are used as a substrate. A compound thin film semiconductor thin film is vapor-deposited thereon. In this method, a peninsular body, a metal, or the like is grown as an ultrathin film having a thickness of several tens to several hundreds of angstroms, and therefore, it is attracting attention as a material that can realize the artificial superlattice structure as described above.

Also, from recent MBE research, it is known that when the reflected electron beam diffraction image during film growth is observed, the reflection intensity of the electron beam changes periodically with time. It has been clarified that the fluctuation period of the light intensity is equal to the time required for further growth of GaAs, for example. The relationship between the state of this vibration and the film growth process is described in Applied Physics, 1985, 54, 698, but a brief explanation will be given.

That is, FIG. 8 is a graph showing the periodic fluctuation of the reflected electron beam intensity, the vertical axis represents the light intensity of the diffraction image, and the horizontal axis represents the time. For example, when the underlying crystal is irradiated with only the As beam, the surface of the film is very flat and the reflection intensity is the same. When both As beam and Ga beam are irradiated, GaAs is formed on the underlying crystal. When the amount of GaAs increased with the passage of time, the intensity of the reflected electron beam began to decrease and was formed.
When the GaAs thin film covers half of the surface, the light intensity becomes minimum.
As the growth progresses further, the intensity of the reflected electron beam begins to increase.
Is maximized when Ga corresponding to covering the entire surface is supplied to the growth surface.

However, the flatness on the atomic scale of the surface after the growth of the first layer is extremely poor as compared with the initial state, and this maximum value is significantly lower than the initial value, reflecting this. As the growth continues, the maximum (a, a ′, a ″ ...) and the minimum (b, b ′, b ″ ...) are repeated, but the partial unevenness on the surface It becomes more pronounced and the amplitude between the maximum and the minimum becomes smaller and smaller.

Therefore, in the MBE method, a method has been proposed in which the intensity of the backscattered electron beam during growth is monitored, and the thickness of the growth layer is strictly controlled by operating the shutter at the time difference of maximum intensity.

That is, this is the phase control epitaxy method. This method utilizes the periodic fluctuation of the intensity of the backscattered electron beam described above, stopping the supply of Ga at the maximum point in the growth of a certain material such as GaAs, and then growing a layer of the next material such as AlAs. The feature is that the thickness of each layer can be controlled by the order of atomic layers.

However, in general, the maximum value of the intensity of backscattered electron beams on the surface having a growth rate of several tens of layers is much lower than the intensity of the backscattered electron beams at the beginning, and therefore the irregularities on the growth surface are significant. In other words, although the above-mentioned phase control Pitakin has good controllability of the layer thickness, the flatness of the hetero interface is not so much improved as compared with the conventional MBE method. By the way, when the Ga irradiation is stopped after the multi-layer growth, the intensity of the reflected electron beam increases. It is considered that this is because Ga diffuses on the surface and the surface becomes flat.

Then, using this principle, a method of improving the flatness of the hetero interface by stopping the growth after a certain amount of growth for a short time was considered. However, when the shutter is closed at the time when the film growth of atoms of several tens of nanometers or more is completed, the time required until the reflected electron beam intensity is restored, that is, the flatness is restored is several minutes to 10 minutes or more. There is a problem as described below. That is, when the growth is stopped for a long time, the surface of the grown film is exposed to residual gas, so that water, carbon, carbon monoxide molecules, etc. present in the gas adhere to the thin film surface, and the next layer grows. When doing, it may be trapped inside the membrane. It is known that such impurities significantly deteriorate the electrical and optical properties of the film, and in this respect, this method for improving the flatness of the hetero interface is extremely disadvantageous.

Further, planar doping, in which only a specific layer is doped, is known as an effective method for manufacturing various devices, but it is required that the doping surface be extremely flat in order to maximize the characteristics of planar doping. . However, in phase control epitaxy, the surface after multi-layer stacking has severe irregularities, and there is no means for removing this, so it is difficult to selectively dope only one layer. In this case, it is possible to obtain a flat atomic surface by taking sufficient recovery time before performing planar doping, but since the recovery time is extremely long, adsorption of carbon impurities and the like occurs, In particular, there arises a problem that the efficiency of n-type doping is greatly reduced.

Further, the present inventors have proposed a more preferable MEB method as Japanese Patent Application No. 60-185193.

In this method, each crystal thin film growth operation on the substrate is repeated while monitoring the backscattered electron image of the grown thin film, and the thin film growth operation is stopped at each intensity peak of the backscattered electron beam so that the intensity of the backscattered electron beam is at the initial value. It is characterized by the operation of restarting the growth operation when it has recovered to at least 90%. As a result, the sharpness of the interface between the thin film layers, the steepness of the dopant concentration, the shortening of the multilayer film formation time, and the purification of the grown thin film, which have been problems in the related art, have been greatly improved.

On the other hand, the epitaxial growth of III-V group compound semiconductors on Si is not suitable for field effect transistors and solar cells.
In recent years, its importance has expanded. There are basically two problems with this technology. One is that, with the exception of GaP, there is a large difference in the lattice constant between the grown thin film and the underlying crystal, and the other is that the thermal expansion coefficients of the grown thin film and the underlying crystal differ greatly from each other.

Since the difference in lattice constant is compensated by the occurrence of misfit dislocations on the compound semiconductor side near the interface, the problem is solved, but it is difficult to compensate for the difference in thermal expansion coefficient. However, in the conventional method of performing epitaxial growth, the growth temperature is relatively high at 600 ° C. to 800 ° C., and therefore, as shown in FIG. It causes a concave warp on the side. Note that FIG. 9 shows the GaAs thin film 112 formed on the Si substrate 111 and the hetero interface 113 between them.

FIG. 10 is a graph comparing the linear expansion coefficients of Si and GaAs. As can be seen from this figure, the difference in linear expansion coefficient is about Δα = (α _GaAs −α _Si ) = 3 × 10 ⁻⁶ / K.

Now, assuming that a GaAs thin film having a thickness of 5 μm is formed at 700 ° C. on a Si substrate having a thickness of 200 μm, the lattice mismatch is caused by the misfit dislocations at the hetero interface of GaAs-Si near the growth temperature. Distortion due to is eliminated and the wafer is flat.

However, when cooled to room temperature, a dimensional difference of up to 0.2% occurs between the Si substrate and the GaAs epitaxial layer,
Large distortion occurs in the wafer. This warp has a curvature R
Is about several meters, and if the wafer diameter is large, the substrate will crack.

This curvature causes many problems when applying this structure to devices. For example, when manufacturing a solar cell, the increase in area is restricted, and Si is used to form a compound semiconductor thin film.
The meaning of using the substrate is diminished. Further, when an integrated structure of the field effect transistor is produced, a photolithography is required, but a fine pattern cannot be used due to the warp, and the degree of integration cannot be increased.

On the other hand, the most effective way to solve the above-mentioned problem is to lower the growth temperature.
It is known that the above temperature is the minimum required, and that the crystallinity of the epitaxial layer is significantly deteriorated when the growth temperature is lowered. That is, in order to grow a good quality crystal, it is essential that the compound semiconductor material supplied to the surface of the underlying crystal is uniformly diffused on the growth surface. However, when the film forming temperature is lowered, the migration of the material element is drastically lowered, and as a result, the material supplied to the surface cannot occupy a thermodynamically stable position and the crystal growth is deteriorated.

Taking GaAs as an example, in the conventional molecular beam epitaxy method (MBE method) and metal-organic vapor phase epitaxy method (MOCVD method), crystal growth is performed under As-stabilizing conditions, so the substance supplied to the surface is Ga. It has a shape close to that of the −As molecule, and the mobility of such molecules on the growth surface is extremely small. For this reason, treatment at high temperature is essential in order to increase this moving ability.

As described above, there are some problems to be solved in order to take advantage of the advantageous features of compound semiconductors that can realize devices such as lasers and HEMTs.

That is, in order to realize a superlattice structure, it is necessary to stack a large number of layers having a thickness of about a monoatomic layer, but the performance of these elements is that the components between layers, the composition steepness, and the doping concentration steepness. Etc. Therefore, the MBE method has attracted attention and has been widely used for this kind of purpose, but the methods proposed hitherto cannot often give sufficient effects. Further, even with respect to a physical problem caused by a difference in coefficient of thermal expansion between the base crystal and the grown film, the conventional method has not been basically improved.

Therefore, the present invention solves the above-mentioned drawbacks of the conventional method, can form a superlattice structure having an even flatter and steeper interface at the atomic layer level, and can form a practical large-area compound semiconductor thin film. It is an object of the present invention to provide a method for forming a novel compound semiconductor thin film to be obtained.

Means for Solving the Problems That is, according to the present invention, group II and VI element beams or group III and V element beams are supplied to the surface of the underlayer crystal, respectively, and II-VI is formed on the underlayer crystal. Tribe or II
In the method of forming a compound semiconductor thin film for growing a compound semiconductor thin film of group IV, a group V or VI element is supplied in an amount less than the amount necessary to cause film growth on the surface of the underlying crystal, and the group V or VI element is supplied. The first operation for supplying the group V element beam to the underlying crystal surface, and the group V or VI element beam to the underlying crystal surface with a sufficient supply amount of the group V or VI element to grow the film on the underlying crystal surface. A second operation of supplying, and a third operation of supplying a group II or group III element beam to the surface of the underlayer crystal in a supply amount sufficient for film growth of the group II or group III element on the surface of the underlayer crystal. The second operation and the third operation are alternately performed while the first operation is constantly performed throughout the thin film formation process, and the II-VI group or III-V group compound semiconductor thin film is used as a base. Compound semiconductors characterized by being formed on crystals The thin film forming method is provided.

INDUSTRIAL APPLICABILITY The method of the present invention can be applied to compound semiconductors in general, and can efficiently mass-produce a compound semiconductor multilayer thin film including a thin film having an atomic layer level with a sharp interface. Further, even when the material element contains a component having a high dissociation pressure equilibrium vapor pressure, no defect due to loss of the component or the like is caused.

In the method of the present invention, a plurality of component element beams of different types as the group III or group II element beam are simultaneously given,
Alternatively, it is also possible to alternately supply them on the substrate to form a multi-layered thin film having a mixed crystal or a heterojunction structure, or including them.

Action As described above, when forming a superlattice structure, a particular problem is the flatness of the atomic dimensions at the interface between adjacent growth layers, the steepness of the doping profile, or the composition steepness between the layers. This is to secure and prevent the occurrence of defects at the interface. For that purpose, it is important to secure the flatness of the surface of the grown thin film for each layer and prevent the escape of the high dissociation vapor pressure component from the growing thin film.

Therefore, in the method of the present invention, the high dissociation equilibrium vapor pressure component is constantly supplied to prevent the escape of the component during the growth, and the atomic beam of the source element is alternately irradiated onto the substrate, thereby Solved the problem.

That is, for example, in the case of GaAs film growth, if Ga is not supplied, As stays on the substrate surface for a certain average residence time,
The change of re-evaporation is repeated, but when Ga is incident,
As and Ga react to form a film. Therefore, at the time of supplying Ga, only a small amount of As beam that suppresses As loss from the growth surface is supplied. Therefore, the probability that Ga atoms that reach the growth surface will react with As atoms to become GaAs,
Ga atoms diffuse well on the growth surface. On the other hand, the supply of a small amount of As atoms suppresses the generation of As vacancies, so that impurities are less likely to be incorporated.

Subsequently, the supply of Ga atoms was stopped, and the amount of Ga required for thin film growth was
By supplying As atoms, the Ga atoms attached to the growth surface and diffused react with the supplied As atoms to form a GaAs thin film.

Thus, it is flat at the atomic layer level compared to the conventional method,
A highly pure growth layer can be obtained.

In addition, when the growth temperature is lowered in the conventional technology (MBE, MOCVD) as described above using the growth of GaAs as an example,
The crystal quality is significantly deteriorated because the mobility of Ga-As molecules supplied to the growth surface is sharply reduced.

However, the present inventors have found that the surface movement speed of Ga atoms is 200 times or more faster than the surface movement of GaAs molecules on the growth surface. That is, the present invention is based on this finding and promotes surface migration of Ga atoms by alternately supplying Ga and As to the growth surface over time, thereby enabling low temperature growth.

The surface moving speed of Ga atoms becomes similar to the moving speed of GaAs molecules at 700 ° C., for example, when the growth temperature is about 100 ° C. Therefore, according to the method of the present invention, the growth temperature of GaAs can be reduced to about 100 ° C. in principle. Also, as described later, by actually applying it on the Si substrate,
We were able to grow high-quality compound semiconductor thin films up to a growth temperature of 150 ° C.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to the drawings. However, the following are merely examples of the present invention, and do not limit the technical scope of the present invention. .

Example I FIG. 1 is a diagram schematically showing the configuration of an apparatus in one example of the method of the present invention.

As shown in the figure, a substrate holder 6 for holding a substrate 5 as a base crystal is installed at a substantially center of the vacuum container 1. Further, the substrate holder 6 is connected to a heating means and a temperature controller 24 connected to the heating means, and has a function of holding the held substrate at a predetermined temperature.

Further, molecular beam sources 3-1 to 3-4 having openings on the side wall of the vacuum chamber 1 facing the substrate 5 are provided. The molecular beam sources 3-1 to 3-4 are cells capable of supplying As, Ga, Al, and As, respectively, and the cells other than the cell 3-1 can be controlled to open / close from the outside by a shutter 4. Is provided.

Further, in the present embodiment, in order to monitor the operation of these MBE devices, means for irradiating the surface of the substrate 5 with an electron beam at an angle of 2 to 3 and measuring the reflection thereof is provided. The measuring means is a fluorescent screen 8 which receives a reflected electron beam.
A television camera 9 for observing the fluorescence pattern on the screen 8 and a CRT monitor 10 for visually observing the information obtained by the television camera 9.

Furthermore, this CRT monitor 10 is used for automatic control and the like described later.
A solar cell 21 for observing the output of the computer and a computer 22 for controlling the opening and closing of the shutter 4 described above are provided via a shutter controller 23 based on information obtained from the solar cell 21.
The computer 22 is also involved in controlling the temperature controller 24 described above. 2 is an ultrahigh vacuum pump such as an ion pump.

The opening and closing of the shutter by the control system can be performed while monitoring the backscattered electron diffraction image during thin film growth,
The grown thin film may be damaged by electron beam irradiation. Therefore, actually, a preliminary experiment is performed while monitoring by reflection electron beam diffraction in advance, and the target layer as shown in FIG. 2 or FIG. 4 is attached. A time chart is obtained for a large number of films of the configuration and input to the computer 22, and the shutter 4 of the molecular beam source 3 is automatically opened / closed in accordance with the time chart to obtain a superlattice or a multilayer film having a desired film configuration. It is preferable.

When doping is required, another molecular beam source is provided and the shutter is opened / closed, whereby selective doping can be performed in a predetermined layer. According to the present invention, since the steepness of the interlayer interface and the flatness of the surface are guaranteed, the steepness of the dopant concentration can be sufficiently ensured.

A GaAs thin film layer and a GaAs / AlAs superlattice were formed on a GaAs substrate according to the method of the present invention by using the apparatus of the present invention provided with four molecular sources as shown in FIG.

2 (a) to 2 (c) show control of each molecular beam source when a GaAs thin film is formed on the substrate 5 using the apparatus shown in FIG. Figure (a) shows As cell 3
-1 control, FIG. 2 (b) controls the Ga cell 3-2,
FIG. 2 (c) shows the control of the As cell 3-4, respectively.

First, the pressure inside the vacuum container 1 is adjusted to 10 ^-10 Tor by the ion pump 2.
After evacuating to an ultra-high vacuum of r or less, heating to about 630 ° C above
As shown in FIG. 2A, the GaAs substrate 5 was irradiated with the As beam from the As cell 3-1 and was constantly irradiated during the film forming operation. The intensity of As beam is about 0.5 × 10 ¹⁴ / cm ² ·
Set to sec. At this intensity, the As beam does not contribute to the growth of the GaAs thin film, but the As beam does not contribute to the growth of the GaAs crystal layer.
As effectively suppresses omission.

Then, the shutter 4 is opened and closed according to the time charts shown in FIGS. 2B and 2C, and the molecular beam source 3-2
Ga beam (Fig. 2 (b)) from the molecular beam source 3-4
The substrate 5 was irradiated with an Aa beam (FIG. 2 (c)) to grow a GaAs thin film.

On the other hand, from the direction almost perpendicular to the above molecular beam,
An electron beam accelerated to 10 KeV was irradiated to the film surface at an angle of 2 to 3 °, and the electron diffraction pattern was received by the fluorescent screen 8. This pattern was photographed by the TV camera 9 and was photographed on the CRT monitor 10. Further, the light intensity of the CRT monitor 10 is detected by the solar cell 21, and the output is plotted. The results are shown in FIG.

Considering FIG. 3 together with FIG. 2, the molecular beam source 3-2
The intensity of the backscattered electron beam drops sharply when the irradiation of Ga beam is started. Next, when the irradiation of the Ga beam is stopped and the irradiation of the As beam is started from the molecular beam source 3-4, the intensity of the reflected electron beam is restored to the position where the growth started.

The formation of GaAs / AlAs superlattice was then carried out by operating the same device according to the time chart as shown in FIG. In addition, the cell 3-3 is used for irradiation of the Al beam,
FIG. 4 (a) shows As controlling the cell 3-1 and FIG. 4 (b).
Is for controlling the Ga cell 3-2, and FIG. 4 (c) is for the Al cell 3-3.
4 (d) shows the control of the As cell 3-4.

That is, as in the case of forming the GaAs thin film described above, the Ga beam is first irradiated from the cell 3-2 while the As beam is constantly irradiated from the cell 3-1. Then, by cell 3-4,
A GaAs thin film is formed on the substrate 5 with a high intensity As beam. Next, after irradiating the Al beam with the cell 3-3,
The cell 3-4 again irradiates an As beam having sufficient intensity to form an AlAs thin film.

Comparing the photoluminescence of the superlattice prepared by repeating this procedure and the one prepared by the phase-controlled epitaxy method, many peaks due to defects were observed in the latter, while the number of those peaks was found in the former. It was found that the peak height of the remaining peaks was drastically reduced as the peak value was drastically reduced.

In addition, according to the time chart obtained in this way, the shutter is automatically opened and closed to form a similar thin film, and the photoluminescence measurement is performed on the obtained thin film.
It was found that the same excellent effect as above was almost completely reproduced.

Further, the same method was also applied to the formation of II-VI group compound semiconductor thin films such as ZnS and ZnSe, but similarly to the conventional method, the optical characteristics of the obtained thin film layer are significantly improved as described above. confirmed.

In addition, in order to prevent the beam of the V or VI element that is steadily irradiated from effectively "leaving" the V or VI element, at least the equilibrium dissociation vapor pressure of the V or VI element of the underlying crystal It is also high, and is set to be less than 10 times that range. For example, for a GaAs thin film at 700 ° C, 0.5 × 10 ¹⁴
Is required to be pieces cm ² · sec~5 × 10 ¹⁴ atoms cm ² · sec.

On the other hand, the second beam intensity must be emitted with an intensity higher than this value. The second beam intensity, since the defect density increases when too high, the upper limit in the example GaAs is 3 × 10 ¹⁵ pieces / cm ² · about sec, the compound semiconductor in general, 15 × 10 ¹⁴ pieces It is preferable that the upper limit is about / cm ² · sec.

Although the As beam is constantly supplied from the As cell 3-1 in the above embodiment, the As beam is supplied only to the As cell 3-1 and the As beam is rotated even if the shutter is closed. If a structure that causes leakage is provided, the As element is supplied in an amount less than that required to form a film on the surface of the underlying crystal, so an As cell shutter having such a structure may be used.

Example 2 In the first example, the method of the present invention was carried out at a temperature substantially similar to that of the conventional molecular beam epitaxy method. However, in the present example, under the low temperature which is another feature of the present invention. The compound semiconductor thin film was formed. That is, in the following examples, a GaAs / AlAs thin film was formed on a Si substrate at a low temperature of 100 ° C to 400 ° C.

FIG. 5 schematically shows the configuration of an apparatus when the present invention is applied to the molecular beam epitaxy method (MBE method). That is, this device has the same structure as a general MBE device, and is a liquid chisso shroud housed in a high vacuum chamber 11 equipped with two ultra-high vacuum pumps 14-1 and 14-2.
The inside of 12 is provided with three molecular beam cells 13-1, 13-2 and 13-3 capable of irradiating the source element beam. Here, cell 13-1 is the As beam and cell 13-2 is the
The Ga beam is configured so that the cell 13-3 supplies the Al beam. In addition, each molecular beam cell 13-1, 13-2, 13-
Each of the shutters 3 is provided with a shutter 18 that is independently controlled to interrupt the irradiation of the beam. Further, the substrate 17, which is the base crystal, is supported in the chisso shroud 12 by the substrate holder 16 having a heating means.

After removing the surface oxide film of the Si substrate 17, the Si substrate 17 is fixed to the substrate holder 16 and the inside of the chisso shroud 12 is 5 × 10 ⁻⁸ Torr to 1 × 10 ⁻⁷ Torr by the ultra-high vacuum pumps 14-1 and 14-2. Exhausted to a degree. At the same time, the Si substrate 17 was heated to an appropriate temperature of 100 to 400 ° C.

Next, the number of Ga atoms required to form one atomic layer on the substrate crystal according to the atomic coordination rule of the zinc blende crystal structure, that is, 6.4 × 10 ¹⁴ when the growth surface is the [001] surface. /cm
Supplied ² atoms.

Next, the supply of Ga atoms was stopped, and the substrate was irradiated with a high intensity As beam. The degree of vacuum at this time is a substrate temperature of 400 ° C.
1 to 2 × 10 ⁻⁶ Torr, and at 100 ° C., 0.5 to 1 × 10 ⁻⁶ Torr.

If an As beam that reacts with the Ga beam described above is supplied, the intensity of the As beam will be reduced and it will be formed on the substrate.
While the strength should be such that As does not escape from the GaAs thin film, II
As a group I element, Al beams were supplied as many times as the number of atoms required for Al atoms to form one atomic layer on the substrate crystal.
After that, the operation from increasing the intensity of the As beam is as described above.

By repeating such operations, GaAs (or AlA
s) is grown, but when Ga (or Al) is supplied, the amount of As that does not contribute to film formation is supplied, so Ga (or Al) atoms can move at high speed on the growth surface, and a uniform thin film at low temperature can be obtained. Growth is realized.

FIGS. 6 (a) and 6 (c) show the timing of beam supply in the above operation.

FIG. 6 (a) shows the beam supply amount of the As cell 14-1, and FIG. 6 (b) shows the beam supply amount of the Ga cell 14-2.
Indicates the beam supply amount of the Al cell 14-3.

Incidentally, the group III element, that is, Ga or Al in this case, must be adjusted so that the number of atoms necessary for forming one atomic layer is supplied in each supply cycle, but this is not highly accurate. 90% of one atomic layer equivalent ~
If it was in the range of 110%, extremely good quality crystals could be obtained. Therefore, this control can be sufficiently achieved by the shutter drive control by a normal computer in which the above timing is programmed.

The specific Ga beam and Al beam supply amounts in this example are 1 second at a Ga cell temperature of 970 ° C. and 1100 ° C. at an Al cell temperature of
Then it is 1.2 seconds. As for the As beam, the pressure ratio with Ga and Al group III elements such as Ga and Al is supplied in the range of P _AS / P _{Ga (Al)} = 1 to 50, and the time is It was 1-2 seconds.

Therefore, the growth rate of GaAs and AlAs was about 0.5 μm / hour, which was a sufficiently practical growth rate.

FIG. 7 shows a GaAs / Si heterowafer grown at a substrate temperature of 200 ° C. by the method of the present embodiment, in which a 5 μm thick GaAs growth layer 72 and a heterointerface GaAs are formed on a 200 μm thick Si substrate 71.
Misfit dislocation 73 occurs on the side. Due to the growth at such a low temperature, the radius of curvature increased to several tens to 100 m, and a very flat wafer was obtained. Similar low temperature growth was also performed when GaAs was used as a substrate crystal, and it was confirmed that a good quality crystal was obtained.

EFFECTS OF THE INVENTION As described above in detail, according to the method for forming a multilayer thin film of a compound semiconductor of the present invention, in the case of a III-V group compound semiconductor, for example, it is necessary to prevent vaporization of group V element atoms from the growth surface, and By irradiating the group V atomic beam that does not contribute and the group V atomic beam and the group V atomic beam having a higher intensity than the above group V beam alternately, the surface is flat at the atomic layer level and no defect is included in the interface. It became possible to fabricate thin films.

Furthermore, not only the above-mentioned III-V group, but also its crystal, a multi-layered film of various film configurations including a heterojunction structure, a superlattice structure can be advantageously obtained, and the same can be applied to the II-VI group. It turned out to give an excellent effect.

Further, according to the method of the present invention, since the group III atoms are supplied onto the underlying crystal in the state where there are not enough group V atoms to react with the group III atoms, these atoms are extremely actively diffused even on the surface at low temperature. It is possible to grow a III-V compound semiconductor at low temperature. Therefore, it was manufactured by this method (III-
In the (V) / Si heteroepitaxial wafer, the warpage due to the difference in the thermal expansion coefficient between the III-V material and Si does not substantially occur.

Therefore, according to the method of the present invention, a superlattice structure such as a III-V group compound semiconductor, which is expected to be the most suitable material for ultra-high speed and high functionality, can be obtained with high quality and high reliability. It also makes it possible to increase the area.

[Brief description of drawings]

FIG. 1 schematically shows the configuration of an apparatus used when the present invention is carried out by the MEB method, and FIGS. 2 (a) to 2 (c) show the apparatus shown in FIG. FIG. 3 is a graph showing the supply timing of each atomic beam when forming a GaAs multilayer film according to the method of the present invention. FIG.
FIG. 4 (a) to FIG. 4 (d) are graphs in which changes in the light intensity of the diffraction image when the growth process of the As multilayer film is observed by reflection electron beam diffraction are plotted against time. FIG. 5 is a graph showing the supply timing of each atomic beam when a GaAs / AlAs superlattice is manufactured according to the method of the present invention using the apparatus shown in FIG. 5. FIG. 2 schematically shows the structure of the device used in the second embodiment, and FIGS. 6 (a) to 6 (c) show a GaAs multilayer film according to the method of the present invention using the device shown in FIG. FIG. 7 is a graph showing the supply timing of each atomic beam when forming the GaAs, and FIG. 7 is a GaAs / S fabricated in the second embodiment of the present invention.
FIG. 8 is a view showing a form of an i-wafer, and FIG. 8 is a view schematically showing a temporal change in the light intensity of a backscattered electron diffraction image observed when a multilayer film is formed by a conventional phase control epitaxy method. , FIG. 9 shows a cross section of a GaAs / Si structure wafer grown by the conventional MBE method, and FIG. 10 is a graph showing the temperature dependence of the linear expansion coefficient of Ga and Si. Is. [Main Reference Numbers] 1, 11 ... Vacuum chamber, 2, 14-1, 14-2 ... Vacuum pump, 3-1, 13-1 ... As molecular beam cell, 3-2, 13-2 ...
Ga molecular beam cell, 3-3, 13-3 ... Al molecular beam cell, 3-4
... As molecular beam cell, 4, 18 ... Cell shutter 5, 17, 84 ... Base crystal substrate, 6, 16 ... Substrate heating holder,
7 ... Electron gun, 8 ... Fluorescent screen, 9 ... TV camera,
10 ... CRT monitor, 12 ... Liquid nitrogen shroud, 15 ... Gate valve, 21 ... Solar cell, 22 ... Computer, 23 ... Shutter controller, 24 ... Temperature controller 71,111 ... Si substrate crystal, 72,112 ... GaAs epitaxial layer , 73, 113… Misfit dislocation layer 90… Hydrogen gas supply port for observation window

Claims (5)

[Claims] 1. Group II and VI elemental beams, or II
A method for forming a compound semiconductor thin film, comprising supplying group I and group V element beams to a surface of a base crystal and growing a compound semiconductor thin film of group II-VI or group III-V on the base crystal. A first operation of supplying a group V or group VI element beam to the surface of the underlayer crystal in a supply amount that is less than the amount necessary for the group VI element to cause film growth on the surface of the underlayer crystal; A second operation of supplying a group V or VI group element beam to the underlayer crystal surface at a supply amount sufficient for the film growth on the underlayer crystal surface, and a group II or III element film forming on the underlayer crystal surface. A third operation of supplying a group II or group III element beam to the underlying crystal surface in a supply amount sufficient for growth, and while the first operation is constantly performed during the entire thin film formation process, Alternate the second operation and the third operation A method for forming a compound semiconductor thin film, comprising forming a II-VI group or III-V group compound semiconductor thin film on a base crystal. 2. A compound semiconductor different from the previous one by supplying a group II or group III element different from the element previously supplied in the third operation and sequentially performing the second operation and the third operation. A method of forming a compound semiconductor thin film according to claim 1, wherein a thin film is formed. 3. In the third operation, one atomic layer equivalent
The method for forming a compound semiconductor thin film according to claim 1 or 2, wherein a group II or group III element beam is supplied. 4. The first, second and third operations are a molecular beam epitaxial method in which a supply element is vaporized in a high vacuum and supplied to a base crystal as an atomic beam or a molecular beam. The method for forming a compound semiconductor thin film according to any one of claims 1 to 3. 5. The compound semiconductor thin film according to any one of claims 1 to 4, wherein the underlying crystal is a Si single crystal substrate whose surface is cleaned. Forming method.