JPH09278596A - III-V group compound semiconductor vapor phase growth method - Google Patents

Abstract

(57) [PROBLEMS] To improve the utilization efficiency of a group V raw material, reduce the consumption of the group V raw material, and decompose the group V raw material by simply modifying the vapor phase growth apparatus. Stabilizes efficiency. According to the present invention, a III-V compound semiconductor crystal is grown by a metal organic chemical vapor deposition method.
It is applied to a vapor phase growth method for a group compound semiconductor. A catalyst 5 for accelerating the decomposition of the Group V raw material is arranged upstream of the crystal substrate 4 with respect to the flow direction of the raw material gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a vapor phase growth method of a III-V group compound semiconductor suitable for epitaxially growing a thin film crystal of a -V group compound semiconductor.

[0002]

2. Description of the Related Art Generally, a thin film crystal of a compound semiconductor is subjected to metal organic chemical vapor deposition (Metal Organic Chemical Vapor Deposition).
Eposition: hereinafter referred to as MOCVD method), epitaxial growth on the substrate surface is performed by feeding a carrier gas containing a plurality of source gases into a substrate heated in a reaction furnace and heating these source gases on the substrate. It is done by disassembling. FIG. 2 shows a schematic diagram of a general horizontal vapor phase growth apparatus. Reference numeral 1 is a reaction furnace of the MOCVD apparatus, 2 is an induction heating coil for heating the susceptor, 3 is a susceptor for holding the substrate, and 4 is a substrate.

The crystal of III-V group compound semiconductor is MOCV
When grown by the D method, the group V raw material is a hydride of a group V element such as arsine (AsH ₃ ) or ammonia (NH ₃ ), and the group III raw material is trimethylgallium (TM).
G) and trimethyl aluminum (TMA) III
Supplied with organic compounds of group elements. The crystal growth rate is
Generally, the supply rate of Group III raw materials is rate-controlled, and V / Group raw materials are V /
III ratio (molar flow ratio of group V element and group III element) is several tens to
It is spilled in tens of thousands. The reason for supplying such a large amount of group V element is that it is necessary to supply a sufficient amount of group V element formed by the decomposition of the group V raw material on the substrate. It can be said that the larger the amount of Group V raw material that must be flowed, the more difficult the Group V raw material is to decompose in the MOCVD furnace.

[0004]

SUMMARY OF THE INVENTION As described above, MOCV
When growing a III-V group compound semiconductor crystal by the D method, there is a problem that a large amount of V group raw material must be flowed. This is because not only the utilization efficiency of the group V raw material is poor, but generally, the hydride of the group V element, which is the raw material of the group V, is highly toxic and combustible. This leads to problems such as the need to increase the size of the detoxifying device and the need to increase the frequency of exchanging detoxifying materials.

For this reason, there is an idea to minimize the supply amount of the group V raw material in the furnace, but if the supply amount of the group V raw material in the furnace is minimized, the decomposition efficiency of the group V raw material is reduced. It needs to be stabilized at all times. However, since a compound of the same group V element acts as a catalyst for the decomposition of the group V raw material, a precipitate (III-
There is a problem that the decomposition efficiency of the group V raw material is affected by the amount of the group V crystal or other V group element compound deposited. In particular, immediately after cleaning the furnace for maintenance or the like, the crystal growth becomes unstable due to the above-mentioned reason. The more I go.

The object of the present invention is to solve the problems of the prior art as mentioned above, improve the utilization efficiency of the group V raw material, and consume the group V raw material by simply modifying the vapor phase growth apparatus. It is an object of the present invention to provide a vapor phase growth method for a III-V group compound semiconductor capable of reducing the amount of impurities and stabilizing the decomposition efficiency of the group V raw material.

[0007]

A first aspect of the present invention relates to a vapor phase growth method of a III-V compound semiconductor for growing a III-V group compound semiconductor crystal by a metal organic chemical vapor deposition method. A catalyst for accelerating the decomposition of the group V raw material is arranged upstream of the substrate in the direction. If a catalyst for accelerating the decomposition of the group V raw material is arranged on the upstream side of the substrate, the decomposition of the group V raw material is promoted. Therefore, even if the flow rate of the group V raw material is reduced, a good surface condition is obtained. -Group V compound semiconductor crystal can be grown. Further, even immediately after cleaning the furnace for maintenance or the like, the crystal growth does not become unstable, and the same film thickness and uniformity as before cleaning can be obtained.

A second invention is the same as the first invention, wherein the catalyst is a compound containing a group V element. The use of a compound containing a group V element for the catalyst is very economical because no raw material other than the crystal raw material is required.

A third invention is the same as the first or second invention, wherein the III-V group compound semiconductor crystal is GaN or Al.
It is an N-type crystal. When the III-V compound semiconductor crystal is a GaN or AlN-based crystal,
Since it is important to promote the decomposition efficiency of the group V raw material, it is effective to promote the decomposition of the group V raw material with a catalyst.

A fourth invention is the same as the third invention, except that the group V raw material is ammonia and the catalyst is nitride, platinum or iron.

A fifth aspect of the present invention is the same as the first to fourth aspects, further comprising means for heating the catalyst.
When the catalyst can be heated, the decomposition of the group V raw material can be further promoted.

For example, when a GaN crystal is grown using TMG as a Group III source material and ammonia as a Group V source material, the crystal growth temperature is usually about 1000.degree. Although the decomposition temperature of ammonia is said to be about 900 ° C, since the raw material gas is flowed in the furnace at a flow rate of several tens to several hundreds of cm / sec, the raw material whose temperature actually rises to the decomposition temperature. The gas is only a small part, and as a result, the V / III ratio has to be made very large. When GaN or AlN is grown in an amorphous state to form a buffer layer, the growth temperature is lower than the decomposition temperature of ammonia 600.
Since it has to be lowered to about 0 ° C., it is more important to promote the decomposition efficiency of Group V raw materials.

The growth conditions around this are J. Crystal Grow
th 98 (1989) 209-219 and Appl.Phys.Lett.48 (5), 3 Feb.198
It is made public by 6 and so on.

Further, arsenic is used as a group V raw material for GaAs.
When growing crystals, the decomposition temperature of arsine is about 30.
At 0 ° C, it is much lower than the crystal growth temperature (about 600 ° C), so the decomposition efficiency does not deteriorate as much as the above-mentioned ammonia, but the temperature of the flowing gas still rises only for the amount of contact with the furnace wall. The reality is that it is not heated enough for decomposition.

Therefore, as in the present invention, on the upstream side of the substrate,
When a substance that serves as a catalyst for accelerating the decomposition of the group V raw material is provided, it is not necessary to take a large V / III ratio even when growing a GaN crystal as described above, and GaN or Al
Even when the material is grown in an amorphous state to use N as a buffer layer, the promotion of the decomposition efficiency of the group V raw material is sufficiently ensured. Further, even when a GaAs crystal or the like is grown using arsine as a group V raw material, the group V raw material can be sufficiently decomposed even if the group V raw material is not heated enough for decomposition.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described together with comparative examples, but for convenience of description, the comparative examples will be described.

(Comparative Example 1) The result of growing a GaN crystal using a conventional MOCVD apparatus as shown in FIG. 2 is shown. A graphite susceptor 3 is installed in a quartz reaction furnace 1, and the susceptor 3 can be heated by an induction heating coil 2. For the crystal substrate 4, 25 mm square (0001) sapphire was used.

First, the substrate is heated to 600 ° C. and AlN
Buffer layer was grown to about 500 Å.
The raw material gas at this time was a mixture of TMA of 8 μmmol / min, ammonia of 3 l / min, and hydrogen as a carrier gas of 2.5 l / min. Then, the substrate temperature was raised to 1000 ° C. to grow a GaN crystal on the buffer layer. The mixing ratio of the source gases during GaN crystal growth was fixed at 20 μmol / min for TMG and 0.5, 1.0, 1.5, 2.0, 2.5, 3.
The change in the surface state of the grown crystal was examined by changing the value to 0 / min in 6 ways. The flow rate of hydrogen, which is the carrier gas, was changed so that the flow rate of the raw material gas was always the same, and the total amount with the ammonia was always 4.5 l / min.

The surface state of the grown GaN crystal was transparent when the flow rate of ammonia was 3.0 and 2.5 l / min, but at 2.0 l / min, white cloudiness was observed on the upstream side of the substrate. When the flow rate was 1.5 l / min or less, the front surface of the substrate became white.

(Embodiment 1) A result of growing a GaN crystal by using the MOCVD apparatus according to the embodiment of the present invention as shown in FIG. 1 is shown. A graphite susceptor 3 is installed in a quartz reaction furnace 1, and a catalyst 5 is installed upstream of the susceptor 3. Catalyst 5 is 10 mm
GaN is grown to a thickness of about 3 μm on a sapphire substrate having a size of 20 mm, and the surface of the susceptor 3 is embedded so that the GaN surface faces upward. The susceptor 3 can be heated by the induction heating coil 2. At this time,
The catalyst 5 is also heated at the same time. Crystal substrate 4
Used 25 mm square (0001) sapphire.

In the same manner as in Comparative Example 1, GaN crystals were grown on the AlN buffer layer while changing the ammonia flow rate, and the dependency of the surface state on the ammonia flow rate was examined.

The result is that the ammonia flow rate is 3.0 to 1.5.
It was possible to grow a transparent GaN crystal during each l / min. When the flow rate of ammonia was set to 1.0 l / min, a slightly cloudy region was observed in the upstream part from the center of the substrate, and under the condition of 0.5 l / min, cloudiness was observed up to the downstream side of the substrate. became.

From the above results, even if the flow rate of the group V raw material is reduced by placing the substance serving as the catalyst on the upstream side of the substrate,
It was confirmed that GaN with a good surface condition could be grown.

(Comparative Example 2) Similarly to the comparative example, an AlN buffer layer was grown under the following conditions using a conventional MOCVD apparatus as shown in FIG. The substrate was heated to 600 ° C., TMA was mixed at 8 μmol / min, ammonia was 2.5 l / min, and hydrogen was mixed as a carrier gas at 2.5 l / min, and the AlN buffer layer was grown for 2 hours. Then, the film thickness distribution of the grown crystal was measured. This growth experiment was carried out in a clean and clean furnace, and further grown twice to compare the film thickness distribution. The results are shown in Table 1.

[0025]

[Table 1]

The film thickness of the crystal immediately after cleaning the furnace body tends to be thinner toward the upstream side, and further tends to be lower than the second time as a whole. It is considered that the crystal film thickness becomes uniform and the growth rate stabilizes after the third growth.

(Embodiment 2) A result of growing an AlN crystal by using the MOCVD apparatus according to an embodiment of the present invention as shown in FIG. 1 is shown. The growth conditions were the same as in Comparative Example 2, and the film thickness distribution of the grown crystal was measured. This growth experiment was carried out in a freshly cleaned furnace, and further grown twice continuously to compare the film thickness distributions. Table 2 shows the results
Shown in

[0028]

[Table 2]

In the growth using the catalyst, even with the crystal immediately after cleaning the furnace body, the film thickness of the same extent as in the second and third growth,
Uniformity was obtained, and the variation in film thickness was within the measurement error range.

In the present invention, it is expected that the surface area of the catalyst required to sufficiently promote the decomposition of the Group V raw material has a minimum necessary value, which is the size of the reaction furnace or the crystal substrate. It cannot be unconditionally specified because it has a property that it greatly changes depending on the area, the type of crystal to be grown, the crystal growth temperature, the pressure, the flow rate of the group III source gas, and the like.

In the above embodiment, the crystal substrate and the catalyst were placed on the susceptor. However, in the MOCVD apparatus of the type that automatically conveys the substrate, the substrate is conveyed onto the susceptor and the tray is placed on the susceptor. The method of putting in is also often used. In this case, in addition to the method of placing the catalyst on a part of the susceptor which is not covered by the tray, a method of placing it on the tray and transporting it together with the substrate can be considered.

It is also possible to install the catalyst on the upstream side of the susceptor, not on the susceptor. In this case, the temperature of the catalyst can be controlled independently of the susceptor temperature.

In order to prevent unnecessary decomposition of the group III raw material and reaction of unnecessary raw material gas other than on the substrate, a method in which the gas introduced onto the catalyst is limited to the group V raw material is also considered.

FIG. 3 shows an example of an MOCVD apparatus incorporating the above-mentioned modified example. In the figure, reference numeral 6 is a tray, and 7
Is a resistance heater. The parts corresponding to those in FIG. 1 are designated by the same reference numerals.

Further, although the MOCVD furnace body structure of the above-mentioned embodiment is shown as a horizontal type, it is possible to use not only a horizontal type but also a vertical type. In this case, it is desirable that the catalyst installed upstream has a structure that does not disturb the flow of the raw material gas. For example, FIG. 4 shows an example of a vertical MOCVD apparatus in which the catalyst 5 has a mesh structure and is installed on the upstream side of the crystal substrate 4.

Further, in the present invention, the position where the catalyst is installed is upstream of the crystal substrate, but it is also effective to install the catalyst in a wide range around the substrate including the upstream of the substrate. Particularly in the case of an apparatus in which the substrate is rotated together with the susceptor, it is important that the catalyst is always arranged upstream of the raw material gas flow regardless of the position of the substrate rotation.

[0037]

According to the present invention, the utilization efficiency of the group V raw material can be greatly improved without major modification of the MOCVD apparatus. As a result, not only the consumption of raw materials can be saved, but also the frequency of maintenance of the device for removing unreacted and unused raw material gas can be reduced.

Further, since the consumption of the group V raw material, which is often a toxic and highly flammable gas, can be reduced, the safety and economy are greatly improved.

Further, since the decomposition efficiency of the group V raw material can be stabilized, the reproducibility and uniformity of the characteristics of the grown crystal are improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a reaction furnace of a horizontal MOCVD apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of a reaction furnace of a horizontal MOCVD apparatus according to a conventional example.

FIG. 3 is a schematic sectional view of a reaction furnace of a horizontal MOCVD apparatus showing a modified example of the present invention.

FIG. 4 is a schematic sectional view of a reaction furnace of a vertical MOCVD apparatus showing another modification of the present invention.

[Explanation of symbols]

 1 Reactor 2 Induction heating coil 3 Susceptor 4 Crystal substrate 5 Catalyst 6 Tray 7 Resistance heater

Claims (5)

[Claims] 1. A metal-organic chemical vapor deposition method III-
In the III-V compound semiconductor vapor phase growth method for growing a Group V compound semiconductor crystal, a catalyst for accelerating the decomposition of the Group V raw material is arranged upstream of the substrate with respect to the flow direction of the raw material gas. A method for vapor phase growth of a III-V group compound semiconductor, comprising: 2. The method for vapor phase growth of a III-V compound semiconductor according to claim 1, wherein the catalyst is a compound containing a V group element. 3. The III-V compound semiconductor crystal is GaN.
Or II, which is an AlN-based crystal.
Method for vapor phase growth of IV compound semiconductor. 4. The III according to claim 3, wherein the group V raw material is ammonia and the catalyst is nitride, platinum or iron.
-A vapor phase growth method for a group V compound semiconductor. 5. A means for heating the catalyst is provided.
5. The vapor phase growth method for a III-V group compound semiconductor according to any one of 1 to 4.