JPH01158721A - Method and apparatus for light irradiation type low temperature mocvd - Google Patents

Abstract

PURPOSE:To obtain a high depositing speed and a preferable crystallinity at a low substrate temperature by radiating an infrared laser beam having a specific oscillation wavelength toward a substrate so held at a low reaction temperature as not to sufficiently thermally decompose material gas, and so exciting the molecular vibration of material molecules in the degree as not to decompose the molecules. CONSTITUTION:In a reaction vessel 10, group V material gas and group III organic metal vapor are introduced from supply pipes 30, 32, and the surface of a substrate 14 is exposed in a flow to be discharged from a discharge tube 34. The substrate 14 is placed on a susceptor 12, material gas molecules are not sufficiently thermally decomposed, but so set to low temperature of 500-550 deg.C for suppressing an epitaxially growing speed to a low value. An infrared laser beam 100 tuned at is oscillation wavelength with the infrared absorption wavelength of the molecules of the group V material is radiated toward the substrate 14 held in such a state. Then, the group V material molecules are very enhanced at its chemical activity, chemically reacted with group III organic metal molecules, thereby epitaxially growing a compound semiconductor crystal of high quality even at a low substrate temperature.

Description

[Detailed Description of the Invention] 1] Industrial Application Field The present invention relates to a light irradiation type low-temperature MOC, VD method and apparatus, in particular, a method and apparatus for MOCVD of a metal compound semiconductor using a group V raw material gas or a group II raw material gas. Concerning improvements in methods and apparatus.

[Prior Art] Compared to Si, compound semiconductors have characteristics such as high speed, low noise, and the ability to obtain direct transition type light emitting elements.

However, in conventional device manufacturing processes, LPE (liquid phase epitaxy) is the only method to obtain epitaxial growth layers, and this LPE method has difficulty growing mixed crystals and cannot be used for small-area substrates. However, there were problems such as not being suitable for integrated circuits or mass production.

In order to solve these problems, in recent years halide VPE
method, MBE method, MOCVD (metal organic chemical vapor deposition) method, etc. have been developed and are rapidly becoming popular.

In particular, the MOC, VD method is a method in which a raw material is supplied as a gas and a thin film is deposited on a substrate through a chemical reaction. It has excellent features such as being able to control the thickness of the grown film simply by controlling the supply amount. Moreover, it is the most effective method in terms of mass production and uniformity.

[Problems to be solved by the invention] However, existing devices <1. This MOCVD method, which has been perfected for small-scale mass production of D, FET, etc.
In order to realize a wider variety of applications and expansion of uses by taking advantage of the advantages of compound semiconductors, it is essential to overcome several challenges.

The first challenge is to develop a more precise film thickness control method. If this issue is solved, it will be possible to improve the performance of heterojunction devices through precise film thickness control and abrupt switching of interface composition, and to apply them to new devices such as superlattice elements.

The second challenge is the development of a technology for heso-epitaxial growth of compound semiconductors on Si substrates.

Substrates other than S1, such as GaAs substrates, have only a small area, are expensive, and have insufficient mechanical strength, making them problematic for mass use in terms of resource conservation and safety. many.

On the other hand, Si substrates have major advantages such as being inexpensive, durable, and have good thermal conductivity.
'T', L, D, LED, solar cells, HE M T
, 3D ICs, and other large new demands are expected.

The third challenge is to lower the epitaxial growth temperature.

That is, the conventional MOC, V
In method D, energy for causing a chemical reaction in the supplied raw material gas is given by heating the substrate.

Lowering the processing temperature at this time is very effective in reducing process-induced defects such as the growth of dislocations, preserving already created device structures, and impurity profiles.

In particular, in compound semiconductors, reduction of processing temperature is an important issue because out-diffusion of group V elements easily occurs.

However, at present, a high growth temperature (700° C. to 750° C.) is essential to obtain good crystal quality, and this has hindered the expansion of the range of applications.

In addition, this third issue, that is, lowering the processing temperature,
This is also deeply related to the first and second issues mentioned above. .

That is, the high growth temperature makes precise film thickness control difficult.

Furthermore, even in the technology of amorphous buffer layers and strained superlattice buffer layers developed in heteroepitaxy on Si substrates, high growth temperatures lead to high dislocation densities, increases in dislocation density, and differences in thermal expansion coefficients between Si and compound semiconductors. This causes residual stress and cracking, which hinders its practical application.

As described above, when the MOCVD method is used, reducing the growth temperature does not bring much merit, and a solution to this problem has been most strongly desired.

Various proposals have been made to lower the growth temperature.

Such proposals include, for example, plasma MOCV, which utilizes chemical reactions using energy such as plasma and light, instead of decomposing source gases and film deposition through thermochemical reactions.
I), optical MOCVD using visible light or far ultraviolet light, etc.

However, although these techniques have certainly enabled growth at low temperatures, they have not led to obtaining deposited films of good quality.

This is because the main effect of the above method is to decompose the raw material molecules in the gas phase, and provides the surface migration energy necessary to settle the constituent atoms that have arrived on the substrate crystal in the correct position in the crystal. This is considered to be because the lack of this effect led to amorphization and the occurrence of defects. Furthermore, in plasma MOCVD, damage to substrate crystals caused by high-energy particles (electrons, ions) also hinders obtaining good film quality.

Furthermore, as a technology related to the present invention, there is an application relating to a method for manufacturing a superlattice semiconductor in which the decomposition of a raw material gas is promoted using light energy (Japanese Patent Application Laid-open No. 144320/1983).

However, this application uses optical energy to decompose the raw material gas itself, and by irradiating infrared laser light to excite the molecular vibrations of the raw material molecules to the extent that the molecules do not decompose, the material gas itself is decomposed. The basic principle is completely different from the present invention in which a compound semiconductor crystal is epitaxially grown on top of the present invention, and furthermore, it is not possible to obtain the same effects as the present invention.

[Objective of the Invention] The present invention has been made in view of such conventional problems, and its purpose is to solve the above-mentioned three problems, especially the third problem, and to achieve high temperature even at low substrate temperatures. Light-irradiated low-temperature MOC that can achieve high deposition rate and good crystallinity
The object of the present invention is to obtain a VD method and apparatus.

[Means for Solving the Problems] In order to achieve the above object, the method of the present invention provides a method for MOCVD of compound semiconductors using group V source gas and group II source gas, in which the source gas sufficiently thermally decomposes the substrate. The reaction temperature is maintained at a low temperature, and the substrate is irradiated with an infrared laser beam whose oscillation wavelength is tuned to the infrared absorption wavelength of the molecules of the group V raw material to excite the molecular vibrations of the raw material molecules to the extent that the molecules do not decompose. This method is characterized in that a compound semiconductor crystal is epitaxially grown on a substrate.

Furthermore, in order to achieve the above object, the apparatus of the present invention includes a reaction vessel which has a susceptor on which a substrate is placed, and which maintains the substrate placed on the susceptor at a low reaction temperature at which the raw material gas is not sufficiently thermally decomposed. , a means for supplying a Group ■ raw material gas and a Group ■ raw material waste to this reaction vessel, and a means for supplying a group III raw material gas and a group III raw material waste to the reaction vessel, and a means for supplying a group
means for irradiating an infrared laser beam tuned to the infrared absorption wavelength of the molecules of the Group source gas, and capable of obtaining good crystallinity at a high deposition rate on a substrate maintained at a low temperature. It is characterized by epitaxially growing compound semiconductor crystals.

Next, the present invention will be explained in more detail.

FIG. 1 shows a schematic diagram of an MOCVD apparatus to which the present invention is applied.

This apparatus includes a reaction container]0 and an infrared laser beam generating section 20.

The reaction vessel 180 is provided with a susceptor 12 heated by a heater or the like and controlled to a constant temperature, and the semiconductor substrate 14 is placed on the susceptor 2 .

The reaction vessel 10 is supplied with group V raw material scum, which is controlled at a constant flow rate by a mass flow controller, etc., via the supply piping 30, and group II organometallic vapor, which is also controlled at a constant flow rate. The dregs containing waste is supplied via a supply pipe 32.

The reaction vessel 10 is controlled so that the internal pressure of the gas thus supplied is a constant value below atmospheric pressure, and the internal gas is fed through an exhaust pipe 34 connected to, for example, a vacuum pump. is exhausted.

The reaction vessel 10 is also provided with an infrared window 16, and the infrared laser beam 100 output from the laser beam generating section 20 passes through the infrared optical system 22 to the infrared window 16. through this window 16 into the reaction vessel 1.
4 is irradiated.

Here, the infrared laser beam generating section 20 is preferably formed as a continuous wave type wavelength tunable infrared laser beam generating section such as a C02 laser beam, and the infrared optical system 22 is In the case shown in the figure, it is formed using mirrors, lenses, etc.

萱佚filtration Next, the present invention will be explained in detail.

The present invention can be applied, for example, to UV laser light MOCVD, plasma M
This method is completely different from a method such as OCVD, which completely decomposes raw material molecules in the gas phase.

The present invention uses infrared laser light (for example, CO2 laser light, etc.)
It focuses on the characteristics of In other words, infrared laser light excites the molecular vibrations of raw material molecules to an extent that does not lead to decomposition of the molecules, causing effective chemical reactions only at or near the substrate crystal surface, resulting in high-quality crystal growth. This is because it can be made to do.

Further, in the present invention, attention was paid to the following characteristics of the MOCVD method. That is, in the MOCVD method, the raw material is supplied as a gas. Therefore, the raw material is basically transparent and can be easily controlled by light. In addition, by reducing the pressure of the raw material gas, the probability of interaction between excited raw material molecules in the gas phase is reduced, which allows the molecules to efficiently reach the substrate crystal surface without causing many side reactions. Well transported.

The present invention focuses on the characteristics of such an infrared laser and MOCVD method, and solves the above-mentioned first to third problems by combining a low-pressure MOCVD method and a vibrational excitation method of raw material molecules using an infrared laser. In particular, it attempts to solve the third problem.

(a) Low substrate temperature, i.e., as mentioned above, molecules vibrationally excited by infrared laser light have a chemical activity of 10 to
It increases by more than 100 times. This excited molecule reaches the surface of the substrate crystal, obtains thermal energy from the substrate, or due to the catalytic effect of the substrate crystal, etc., becomes the second raw material molecule (
(or raw material atoms) and become effectively incorporated into the substrate crystal.

Note that in the gas phase, excited molecules are quickly deactivated and are unlikely to react. Because of this, giant raster to microcrystalline powder is not generated in the gas phase in a space away from the substrate, and high-quality epitaxial growth progresses only on the substrate crystal surface.

This reaction requires only a small amount of thermal energy from the substrate surface, and the only other energy required is to impart a small amount of surface dynamic energy to the decomposed atoms.

Therefore, according to the present invention, compared to the conventional MOCVD method,
The above-mentioned reaction can be carried out sufficiently even if the temperature of the substrate is lowered, and thus the present invention allows the epitaxial growth temperature to be lowered.

(b) Material selectivity Furthermore, as is well known, the infrared absorption spectrum of a molecule exhibits a very sharp peak, and if the infrared light wavelength shifts slightly, the absorption becomes extremely small.

The present invention, which utilizes the infrared absorption of molecules, has excellent material selectivity by tuning the oscillation wavelength of the infrared laser beam to the infrared absorption of the raw material molecules.

That is, by tuning the oscillation wavelength of the infrared laser beam to the infrared absorption of the raw material molecules, it is possible to excite only the raw material molecules, without affecting the impurity gas contained in the raw material at all. This point is clear in the conventional MO using UV laser light.
This is significantly different from a method such as CVD, which excites and decomposes not only raw material molecules but also all impurity molecules.

In this way, even if raw materials with low purity are used in the present invention,
It has the excellent feature of being able to obtain epitaxially grown crystals of good quality.

(C) Precise film thickness control Furthermore, when infrared laser light is used as in the present invention, it is possible to significantly change the growth rate by turning the infrared laser light on and off. It becomes possible to instantly change the growth rate and perform precise film thickness control and steep composition control without being limited by slow response times such as switching.

In this way, the present invention can solve the first problem.

(d) Utilization of Si substrate In addition, in the present invention, as mentioned above, the epitaxial growth temperature can be lowered, so generation of stress due to difference in coefficient of thermal expansion, increase in dislocation density, etc. can be suppressed. This provides the possibility of solving the second problem and opens the way to enable heteroepitaxial growth of compound semiconductors on Si substrates.

"action" Next, the present invention will be explained in detail.

First, in this MOCVD apparatus, the intake and exhaust of the raw material gas into the reaction vessel]0 is performed as follows.

Group (1) raw material gas whose flow rate is controlled to be constant by a mass flower (not shown) or the like is introduced into the reaction vessel 10 via the supply pipe 30.

Similarly, group (2) organometallic vapor, which is not controlled to have a constant flow rate using a constant temperature bubbler, a mass flow controller (not shown), etc., is supplied to the reaction vessel 1 through the supply piping 32.
Introduced within 0.

The raw material gas introduced into the reaction vessel 10 in this manner is exhausted by a vacuum pump (not shown) connected to the exhaust pipe 34. Thereby, the inside of the reaction vessel 10 is maintained at a predetermined pressure below atmospheric pressure.

In this way, a steady flow of raw material gas introduced from the supply pipes 30, 32 and discharged from the exhaust pipe 34 is created in the reaction vessel 10 under reduced pressure, and the substrate is included in this flow. ]-4 surface will be exposed.

By the way, in order to grow crystals on such a substrate 14, it is necessary to heat the substrate 14 to a predetermined temperature. For this reason, in the figure, the substrate 14 is placed on a susceptor 12 which is heated by a heater or the like, and is heated and maintained at a predetermined temperature.

This temperature is the same as the conventional MOCVD temperature.
In the method, the temperature is set at 650 to 750°C.

Therefore, in this conventional method, the raw material gas molecules that have reached the surface of the substrate 14 are decomposed by heat to generate group (I) and group V atoms, which are incorporated into the substrate crystal structure and allow the compound semiconductor crystal to grow epitaxially. I will do it.

In the method and apparatus according to the present invention, the temperature of the substrate 14 is set to a predetermined low temperature, preferably a low temperature of 500 to 550°C. At this temperature, the source gas molecules are not sufficiently thermally decomposed, and the epitaxial growth rate is kept very low.

The present invention aims at the substrate 14 maintained in such a state,
This method is characterized by irradiating an infrared laser beam 100 whose oscillation wavelength is tuned to the infrared absorption wavelength of the molecules of the V group raw material to epitaxially grow compound semiconductor crystals on the substrate surface.

In the device shown in the figure, an infrared laser beam 100 oscillated and outputted from an infrared laser beam generating section 20 is transmitted to an infrared optical system 22.
The beam is shaped into a predetermined beam shape, beam cross-sectional area, and direction, and is introduced into the reaction vessel 10 through an infrared window 16 to irradiate the substrate 14 at a predetermined incident angle.

At this time, the oscillation wavelength of the infrared laser beam 100 is tuned to the strong absorption wavelength of the V group raw material gas.

When the infrared laser beam 100 is irradiated onto the substrate 14 in this way, the infrared laser beam 100 is efficiently absorbed only by the group (III) raw material gas molecules that are physically adsorbed near the substrate surface or on the substrate surface, and the vibrations of these molecules excite.

The group V raw material molecules vibrationally excited in this way are -18
~ Its chemical activity becomes extremely high and chemical reactions occur on or near the substrate surface with Group II organometallic molecules adsorbed on the substrate surface, or with a very small amount of Group III metal atoms generated by thermal decomposition. , epitaxially grows as a compound semiconductor crystal on the surface of the substrate.

In this manner, according to the present invention, epitaxial growth of high-quality compound semiconductor crystals can be achieved even at a substrate temperature 150 to 250 degrees Celsius lower than that in normal MOCVD.

Further, as described above, the present invention, which utilizes the infrared absorption of molecules, has excellent material selectivity by tuning the oscillation wavelength of the infrared laser beam to the infrared absorption of the raw material molecules.

Therefore, by tuning the oscillation wavelength of the infrared laser beam to the infrared absorption of the raw material molecules, it is possible to selectively excite only the raw material molecules, and as a result, even if raw materials with low purity are used,
It has the excellent feature of being able to obtain epitaxially grown crystals of good quality.

Further, according to the present invention, the epitaxial growth rate is determined by the supply amount of vibrationally excited Group V raw material gas molecules,
Furthermore, the epitaxial growth rate can be freely controlled by adjusting the intensity of the infrared laser beam.

This situation is shown in Figure 2. The horizontal axis shows the reciprocal of the substrate temperature (absolute temperature) (multiplied by 1000), the vertical axis shows the growth rate, and both the horizontal and vertical axes are expressed in logarithmic memory.

In the same figure, the curve with attached symbol 0 is the characteristic curve of normal MOCVD that has been used conventionally, and the attached symbol ]-52,
... is a characteristic curve of the growth rate according to the present invention, and infrared laser light is irradiated onto the substrate 14 in accordance with the order]00
The intensity of is increasing.

[Effects of the Invention] As explained above, according to the present invention, practical epitaxial growth of compound semiconductors can be realized even at a low substrate temperature of 150 to 250°C compared to conventional MOCVD, and high processing speed is achieved. This has the effect that the occurrence of various defects caused by temperature, destruction of already created element structures, etc. can be suppressed to a very low level.

Furthermore, according to the present invention, only the raw material molecules can be selectively excited using an infrared laser beam whose oscillation wavelength is tuned to the infrared absorption of the raw material molecules, so even if raw materials with low purity are used. This has the effect of making it possible to obtain high quality epitaxially grown crystals.

Furthermore, according to the present invention, an infrared laser beam of 0N10FF
The growth rate can be controlled by adjusting the
Compared to conventional means such as adjusting the flow rate of raw material gas,
It enables much faster response and flexible control, allows precise control of the thickness of the grown layer, and steep switching of the composition of the grown layer, compared to the conventional MO.
It has the effect of being able to solve most of the problems in CVD.

[Example] Next, a preferred example of the present invention will be described based on the drawings. Note that the same reference numerals are given to the members corresponding to those of the apparatus shown in FIG. 1, and the explanation thereof will be omitted.

Figure 3 shows a preferred example of the MOCVD apparatus according to the present invention, and in this embodiment, the case of epitaxial growth of gallium arsenide (GaAs), a compound semiconductor, is taken as an example. explain.

In addition, various combinations are possible as the raw materials used in this case, but in the example, arsine (AsH3) and trimethiflepotassium ((CH3)3Ga, "T" MG)
An example using . In addition, triethyl gallium (TEG),) butyl gallium ((C4H9)
3 Ga) and the like can also be used.

Strict gas false value too First, the flow of raw material gas will be explained.

The apparatus of the embodiment has a cylinder 40 filled with As I (3) as the group V raw material waste, and As H3 is used diluted to about 10% with Tofu hydrogen < H2.

5.The AsH3 gas supplied from the cylinder 40 is
The mass flow controller 1 is controlled to have a constant flow rate using the roller 42, and is introduced into the reaction vessel 10 via the supply piping 30.

In addition, the apparatus of the embodiment is capable of producing "T" which is an organometallic material of group
'MG bubbler 50, which is normally maintained at a constant temperature of 0° C. by a constant temperature device (not shown).

Further, in order to transport the organic metal, the apparatus of the embodiment is provided with a carrier gas cylinder 52, and in this cylinder 52, hydrogen (I2) is normally used as a carrier gas.
) is filled with gas. After impurities are removed from the hydrogen gas supplied from this cylinder 52 by a hydrogen purifier 54, it is sent into a 1゛MG bubbler 50 and then
Pass through G. At this time, the hydrogen gas will contain TMG equivalent to the saturated vapor at that temperature,
In this way, the hydrogen gas containing TMG is controlled to have a constant flow rate by the mass flow controller 1 to the roller 56, and is introduced into the reaction vessel 1-0 via the supply pipe 32.

In this way, A s H3 and '
I'MG is supplied, and the ratio of the supply amount is usually 50-1.
It is set to about 00.

The raw material gases such as AsH3, TMG, and hydrogen that have passed through the reaction vessel 10 are exhausted by a rotary pump 60 connected to the exhaust pipe 34.

The exhaust speed at this time is determined by the variable conductance valve 62.
The pressure inside the reaction vessel 10 is adjusted by
It is maintained at a predetermined pressure below atmospheric pressure.

Note that the total pressure is generally set to about 1 to several + TGrr, and usually about 10 Torr. In this case, the AsH3 partial pressure is 0.5 to I Torr, and the TMG partial pressure is 0.0
05 to 0.01 Torr.

In addition, in the same figure, a turbo molecular pump 64 and a rotary pump 66 represent the reaction vessel 1 before epitaxial growth.
-0 is used for cleaning.

In this way, in the apparatus of the example, a steady flow of raw material gas is created in the reaction vessel 10 under reduced pressure, and the substrate]
The surface of -4 will be exposed to this flow.

Next, the temperature of the substrate 14 exposed to the steady flow of source gas will be explained.

The apparatus of this embodiment is provided with a shield 70 for heating the susceptor, and the substrate 14 is placed on the heated susceptor 12 and controlled to a predetermined substrate temperature.

At this time, various methods can be considered to control the substrate temperature, but in this embodiment, a temperature measurement window 74 is provided in the reaction vessel 10, and the substrate temperature is measured by a radiation thermometer 76 through this window 74. Measuring. Then, the measured output is fed back to the temperature regulator 72 to heat the
The power supplied to the controller 70 is controlled.

This substrate temperature is the same as that of the conventionally used normal MOC.
In the VD method, the temperature is set in the range of 650 to 750°C, but in the case of the present invention, the temperature is set at a temperature at which sufficient thermal decomposition of the raw material does not occur.

As in the example, A s H3 and 'I' M are used as raw materials.
When combined with G, the substrate temperature is 500~5
It is set in the range of 50°C. In such a low substrate temperature range, conventional MOCVD
However, the growth rate was slow and the film quality was poor, so it was almost never put to practical use.

In contrast, in the present invention, even in such a low substrate temperature range, a compound semiconductor crystal can be epitaxially grown favorably by using infrared laser light, which will be described below.

A feature of the present invention is that the substrate 1 kept at a low temperature
4, the purpose is to irradiate an infrared laser beam 100 whose oscillation wavelength is tuned to the infrared absorption of the molecules of the group II raw material.

The incident light of this infrared laser beam 100 can be set at any angle in the range of 0° to less than 90°, or in the embodiment
° is set.

Furthermore, in consideration of the absorption band of AsH3 used as the group V raw material gas, the infrared laser light generating section 20 used in this embodiment is formed as a C02 laser light generating section having a variable wavelength function. There is. The wavelength of this CO2 laser beam 100 is set to the 10P12 oscillation line (10,513 μm) where ASH3 molecules exhibit strong absorption.

The infrared laser beam 100 oscillated and outputted from the infrared laser beam generator 20 is shaped into an appropriate beam shape and direction by an infrared optical system 22 composed of mirrors, lenses, shutters, attenuators, etc. The infrared light is adjusted and transmitted through the infrared window 16 and irradiated onto the substrate 14 .

Note that the optical system 22 for infrared light can be composed of any combination of members depending on the purpose, and can be omitted when a small-area substrate is used or when local deposition is the purpose.

In this way, the infrared laser beam 1 irradiated onto the substrate 14
00 is absorbed by the As 83 molecule and excites its molecular vibrations. The vibrationally excited 7':ASH3 molecules increase their chemical activity and cause TMG molecules or some thermal decomposition to occur on or near the substrate surface, despite the low substrate temperature range where no reaction normally occurs. Gallium (
It chemically reacts with Ga) atoms to become Ga As and epitaxially grows on the substrate crystal.

Figure 4 shows such epitaxial growth, where the horizontal axis represents the reciprocal of the substrate temperature (absolute temperature) (100
(multiplied by 0), the vertical axis is the growth rate, and both are expressed on a logarithmic scale.

Further, the parameter is the output of the laser beam 100. As is clear from the figure, when the substrate 14 is irradiated with the laser beam 100, the growth rate is low, but when the laser beam output is 20 W or more, the growth rate increases even at a substrate temperature of 600°C or more. It is the same or better, and the film quality is also improved, making it practical.

As explained above, according to the present invention, the normal MOC
, V D , practical epitaxial growth of a GaAs compound semiconductor can be realized even at a substrate temperature 150 to 250° C. lower than that of V D .

Figure 5 shows a second preferred embodiment of the present invention.
The feature of this embodiment is that, as described above, the substrate 14 is irradiated with the infrared laser beam 100 and at the same time, the substrate 14 is irradiated with the ultraviolet light 200, thereby making it possible to obtain higher crystal quality.

That is, in the apparatus of the embodiment, an ultraviolet light window 80 is provided above the reaction vessel 10, and ultraviolet light 200 emitted from an ultraviolet light source 82 provided outside the reaction vessel 10 is transmitted through the window 80. The surface of the substrate 14 is irradiated with the light.

At this time, the wavelength of the light included in the ultraviolet light 200 needs to be set within a range that does not directly photodecompose group (I) organometallic molecules.

As such an ultraviolet light source 82, various types can be used, such as a low-pressure mercury lamp, an ultra-high-pressure mercury lamp, and an excimer laser beam, and in the embodiment, an ultra-high-pressure mercury lamp is used.

Further, in the embodiment, the incident angle of the ultraviolet light 200 is set to 0°, that is, the ultraviolet light 200 is set to be irradiated perpendicularly to the substrate ]-4.

In the apparatus of the embodiment, the surface of the substrate 14 is irradiated with the infrared laser beam 100 from the infrared laser beam generator 20 and simultaneously irradiated with the ultraviolet light 200 from the ultraviolet light source 82.

At this time, the ultraviolet light 200 causes electronic excitation of group (I) organic metals or excitation of radicals such as methyl groups (CH3) generated by its decomposition on or near the substrate surface.
It effectively promotes the chemical reaction between the group V raw material and the group II raw material and the promotion of surface migration before each atom settles on an appropriate site of the substrate crystal, contributing to improving the crystallinity of the epitaxially grown layer.

As an example of this, for example, controlling the substrate temperature to 500°C,
Using a non-doped GaAs layer grown by a conventional MOCVD method and a C02 infrared laser beam 1-00 using the apparatus of the present invention,
Compare the film quality with that of non-doped GaAs grown by irradiating ultraviolet light of 200 ml with a mercury lamp. As a result, the carrier density, which indicates impurity contamination, decreased to 1/20, and the half-width of hole mobility and photoluminescence peak, which indicate improved crystallinity, were 1.5 times and 173 times, respectively, which were significantly increased. An improvement in film quality was confirmed.

The above characteristics are equivalent to or higher than that of a non-doped GaAs layer grown by a normal MOCVD method at a substrate temperature of 650° C. or higher.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible within the scope of the invention.

For example, in the first and second embodiments, the case where A s H3 and trimethyl gallium are used as the group V raw material gas and the group (III) organic metal was explained as an example, but the present invention is not limited to this. It goes without saying that the invention is also applicable to compound semiconductors using other Group V raw material gases and Group (2) raw material gases.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of a light irradiation type low-temperature MOCVD apparatus to which the present invention is applied; FIG. 2 is an explanatory diagram of the low-temperature growth effect according to the present invention; and FIG. 3 is a preferred first embodiment of the apparatus according to the present invention. FIG. 4 is an explanatory diagram of the measurement results of the low-temperature growth effect obtained using the apparatus shown in FIG. 3. FIG. 5 is an explanatory diagram of a second preferred embodiment of the present invention. 10... Reaction vessel 12... Susceptor 14... Substrate 20... Infrared laser light generating section 30.32... Supply piping 34... Exhaust pipe 40.52... Cylinder 50...・ Bubbler-32=70 ... Heater 82 ... Ultraviolet light source 100 ... Infrared laser light 200 ... Ultraviolet light

Claims (4)

[Claims] (1) In the MOCVD method for compound semiconductors using group V source gas and group III source gas, the substrate is kept at a low reaction temperature at which the source gas is not sufficiently thermally decomposed, and the oscillation wavelength is directed toward this substrate to match the molecules of the group V source material. A light irradiation type that epitaxially grows compound semiconductor crystals on a substrate by irradiating infrared laser light tuned to the infrared absorption wavelength and exciting the molecular vibrations of raw material molecules to the extent that the molecules do not decompose. Low temperature MOCVD method. (2) A light irradiation type low temperature method according to claim (1), characterized in that infrared laser light is irradiated while the substrate temperature is maintained at a low temperature in the range of 500 to 550°C. MOCVD method. (3) A reaction vessel having a susceptor on which the substrate is placed, and maintaining the substrate placed on the susceptor at a low reaction temperature at which the raw material gas is not sufficiently thermally decomposed; A means for supplying a group raw material gas and a substrate kept at a predetermined low temperature with an oscillation frequency of V.
a means for irradiating an infrared laser beam tuned to the infrared absorption wavelength of the molecules of the group raw material gas; A light irradiation type low temperature MOCVD device characterized by epitaxially growing crystals. (4) The apparatus according to claim (3), including means for irradiating the substrate with ultraviolet light whose wavelength is set in a range that does not directly photodecompose group III organometallic molecules,
A light irradiation type low temperature MOCVD apparatus characterized in that it is formed to simultaneously irradiate infrared laser light and ultraviolet light.