JPH03132017A - Method of forming crystal - Google Patents

Abstract

PURPOSE:To obtain a high quality III-V compound single crystal efficiently and with a high growth speed by a method wherein creation of seeds on a non-seed-forming surface is avoided and a single seed is created on a seed forming surface only in the initial stage of seed forming and a raw material density is increased in a growth stage. CONSTITUTION:A thin film 2 made of material whose crystal seed forming density is low (for instance non-single-crystalline SiO2) is built up on a quartz substrate 1 to form a non-seed- forming surface 3. Non-single-crystalline Al2O3 layers 4 which have a higher seed forming density than the surface 3 are formed. The area of the layer 4 is not larger than 2mum square, i.e., the area in which only one seed can be formed. II-V compound crystal seeds 9 are created by an MOCVD method. In an initial stage, a reaction pressure is selected to be 0.1Torr and a V-group/III-group mol ratio of raw gas is selected to be non less than 45 to avoid the defects caused by the lack of V-group atoms. In the growth stage of single crystals 10 after the crystal seeds 9 are made to grow, the reaction pressure is selected to be the atmospheric pressure and the V-group/III-group mol ratio is selected to be not less than 28 to avoid the waste consumption of the V-group raw material. After that, the crystals are made to grow horizontally onto the non-seed-forming surface 3. With this constitution, the high quality III-V compound single crystals can be obtained efficiently and with a high growth speed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a III-V group compound crystal and a method for forming the same, and in particular, a crystal formed by utilizing the difference in the nucleation density of the deposited material depending on the type of the deposition surface material. The present invention relates to a method for forming (1)-V group compound single crystals or (2)-V group compound polycrystals with controlled particle sizes.

The present invention is applied to the formation of crystals such as single crystals and polycrystals used for, for example, semiconductor integrated circuits, optical integrated circuits, optical devices, and the like.

[Prior Art] Conventionally, single-crystal thin films used in semiconductor electronic devices, optical devices, and the like have been formed by epitaxial growth on single-crystal substrates. For example, it is known that Si, Ge, GaAs, etc. are epitaxially grown on a Si single crystal substrate (silicon wafer) from a liquid phase, gas phase, or solid phase, and GaAs, Ge, etc. are grown on a GaAs single crystal substrate (silicon wafer).
It is known that single crystals such as aAlAs can be epitaxially grown. Using the semiconductor thin film thus formed, semiconductor elements, integrated circuits, light emitting elements such as semiconductor lasers and LEDs, etc. are manufactured.

In addition, recently there has been much research and development into ultrahigh-speed transistors using two-dimensional electron gas and superlattice devices using quantum wells. (molecular beam epitaxy) and MOCVD
(organometallic chemical vapor phase method) and other high-precision epitaxial technologies.

In such epitaxial growth on a single crystal substrate, it is necessary to match the lattice constant and thermal expansion coefficient between the single crystal material of the substrate and the epitaxial growth layer. If this alignment is insufficient, lattice defects will develop in the epitaxial layer. Additionally, elements constituting the substrate may diffuse into the epitaxial layer.

Thus, it can be seen that the conventional method of forming a single crystal thin film by epitaxial growth largely depends on the substrate material. Mathews et al. investigate combinations of substrate materials and epitaxially grown layers (EPITAXIAL
GROWTH, Academic Press, Ne
w York.

1975 ed. by J.W. Mathews).

Furthermore, the size of the substrate is currently about 6 inches for St wafers, and the increase in the size of GaAs+sapphire substrates has been delayed even further. In addition, single crystal substrates are expensive to manufacture, resulting in a high cost per chip.

As described above, in order to form a single-crystal layer from which a high-quality device can be manufactured by the conventional method, there is a problem in that the types of substrate materials are limited to an extremely narrow range.

On the other hand, research and development of three-dimensional integrated circuits, in which semiconductor elements are stacked in the normal direction of a substrate to achieve high integration and multi-functionality, has been actively conducted in recent years, and there has also been active research and development in three-dimensional integrated circuits, in which semiconductor elements are stacked in the normal direction of a substrate. Research and development of large-area semiconductor devices, such as solar cells arranged in a pattern and switching transistors for liquid crystal pixels, is becoming more active year by year.

What these two methods have in common is that they require a technique for forming a semiconductor thin film on an amorphous insulator and forming electronic elements such as transistors thereon. Among these, a technique for forming a high quality single crystal semiconductor on an amorphous insulator is particularly desired.

When a thin film is deposited on an amorphous insulating substrate such as SiO□ during boat fishing, the crystal structure of the deposited film becomes amorphous or polycrystalline due to the lack of long-range order in the substrate material. Here, an amorphous film is one in which short-range order at the level of the nearest neighbor atoms is preserved, but no longer-range order exists.
A polycrystalline film is a collection of single crystal grains that do not have a specific crystal orientation and are isolated by grain boundaries.

For example, when forming SL on SiO□ by the CVD method, if the deposition temperature is below about 600°C, it will become amorphous silicon, and if the temperature is higher than that, the grain size will be between several hundred and several thousand. This results in distributed polycrystalline silicon. However, the grain size and distribution of polycrystalline silicon vary greatly depending on the formation method.

Furthermore, by melting and solidifying the amorphous or polycrystalline film using an energy beam such as a laser or a rod-shaped heater,
Polycrystalline thin films with large grain sizes on the order of microns or millimeters have been obtained (Single-crystal 5
ilicon on non-single-crys
talinsulators, JouIIIal of
Crystal Growth vol.

63, No, 3. 0ctober 1983 ed
ited by G, W.

(:ullen).

When a transistor is formed in the thin film of each crystal structure formed in this way and the electron mobility is measured from its characteristics,
~0.1 cm”/V-see for amorphous silicon
For polycrystalline silicon with a grain size of several hundred, 1 x lO
cm''/V-sec, polycrystalline silicon with a large grain size obtained by melting and solidification has a mobility comparable to that of single crystal silicon.

This result shows that there is a large difference in electrical characteristics between an element formed in a single crystal region within a crystal grain and an element formed across a grain boundary. In other words, the deposited film on an amorphous layer obtained by the conventional method has an amorphous or polycrystalline structure with a grain size distribution, and the devices fabricated there have a higher level of performance than those fabricated on a single crystal layer. As a result, its performance will be greatly degraded. Therefore, its applications are limited to simple switching elements, solar cells, photoelectric conversion elements, etc.

In addition, the method of forming polycrystalline thin films with large grain sizes by melting and solidifying requires a large amount of time to increase the grain size because the amorphous or single crystal thin film is scanned with an energy beam on each wafer. It has the problem that it has poor performance and is not suitable for large-area applications.

On the other hand, ff1-V group compound semiconductors can be used for ultra-high-speed devices,
Although it is expected to be a material that can realize new devices such as optical devices that cannot be realized with Si, ■-V group compound crystals have so far been produced only on Si single crystals or n'+-V group compound single crystals. This has been a major obstacle in device production.

In order to solve the above-mentioned conventional problems, the present inventor has developed a material that has a sufficiently thicker nucleation density than the non-nucleation surface material (and to the extent that only a single nucleus grows) on a non-nucleation surface with a low nucleation density. We have proposed a formation method in which a sufficiently fine nucleation surface is provided on the nucleation surface, and a crystal is formed by continuing growth centering on a single nucleus grown on the nucleation surface, and it is possible to form a crystal even on a non-single crystal substrate. It was shown that it is possible to form single crystals of group V compounds.

This formation method involves artificially separating the nuclei that will grow into a single crystal to a desired distance, allowing them to form selectively, and then contacting and colliding the crystal grains until they grow into a crystal region of the required size. It is something to avoid.

As a crystal growth method, the metal organic chemical transport method (MOCVD method) has a fast growth rate, excellent mass productivity, and good crystallinity.
is mainly used.

[Problems to be Solved by the Invention] However, the above invention is insufficient to control nucleation on fine nucleation surfaces by MOCVD, and nucleation may occur on non-nucleation surfaces. , problems such as nucleation not occurring on the nucleation surface sometimes occurred.

Therefore, an object of the present invention is to suppress the uncontrolled generation of nuclei on non-nucleation surfaces by setting growth conditions suitable for the initial stage of nucleation and the stage of crystal growth, thereby producing high-quality III-V compound single crystals. The goal is to provide a method to grow selectively.

[Means for Solving the Problems] In order to solve the above problems, in a method for forming a crystal of an m-v group compound by a modified metal chemical transport method, a non-nucleation surface with a low nucleation density and a non-nucleation surface of the non-nucleation A substrate having a free surface adjacent to a nucleation surface having a nucleation density greater than that of a surface and having an area small enough to form a unique nucleus that grows into a single crystal. To,
At the initial stage of nucleation, the concentration of the raw material gas is lowered (and at the crystal growth stage, the concentration of the raw material gas is set higher than the initial stage of nucleation).
A method for forming a crystal is provided, which comprises performing a crystal growth treatment.

The method for forming a crystal of the present invention is based on the fact that the adhesion coefficients x, y, and z of atoms of the crystal material on each of the non-nucleation surface, nucleation surface, and crystal surface have a relationship such that z>y>x. In the initial stage of nucleation, in which a single nucleus is formed on the nucleation surface provided on the nucleation surface, in order to increase the selectivity of nucleation, the concentration of group (III) and group III source gases in the supplied gas is adjusted. Lower the probability of nuclear generation. Then, when nucleation on the nucleation surface is completed and lateral growth on the non-nucleation surface has begun (crystal growth stage), the raw material gas concentration is raised to a higher concentration than in the initial stage of nucleation. It promotes crystal growth.

Next, the relationship between the generation of crystal nuclei and the concentration of the source gas will be explained.

FIG. 4 shows the relationship between the density of GaAs crystal nuclei generated on various films and the concentration of the source gas.

Growth conditions Nitrimethylgallium (TMG) Tertiary butyl arsenic (TBAs) V/I11 10 Diluent gas Hz IOA/min Reaction pressure
80 torr Substrate temperature: 670°C Growth time: 5 minutes As is clear from Figure 4, materials with high nucleation density (e.g. Al20m, Ta20a) do not change the nucleation density even if the concentration of the raw material gas in the supplied gas changes greatly. is small, but materials with low nucleation density (e.g. 5in2.5iJ
4) has a strong correlation between the raw material gas concentration and the nucleation density. Especially in the region where the raw material gas concentration is low, Aliam, Ta
The difference in nuclear density between , Os and Sing, 5isNa is considerably large, resulting in favorable selectivity during crystal growth. However, as the raw material gas concentration decreases, the crystal growth rate slows down. Therefore, in actual crystal growth, these factors must be balanced.

It is desirable to select conditions that allow for

Next, embodiments of the present invention will be explained with reference to the drawings.

FIGS. 1(A) to 1(E) are schematic process diagrams showing the process of i-selective nucleation to produce a single crystal of a group 1-v compound with length b by the method of the present invention.

(A): Base material l (for example, A1.0., AIN,
Ceramics such as BN, quartz, high melting point glasses, W, M
A thin film 2 made of a material with a low crystal nucleation density (for example, 5iOz, 5isN4, etc., which is non-single crystal such as amorphous or polycrystalline) is deposited on a non-nucleated lunar surface 3. do. To form this thin film, methods such as the C20 method, the batter method, the vapor deposition method, and the coating method using a dispersion medium are used. Alternatively, as shown in FIG. 1(F)], the base material 1 may not be used, and the material support 5 having a low nucleation density may be used (((A))(B); Non-nucleation Materials with higher nucleation density than surfaces (non-single crystal Aliam, AIN, Ta2e
s, Tio2. wo3, etc.) to form a sufficiently small area (preferably 10 μm square or less, optimally 2 μm square or less) to form a single single-crystal nucleus, and use it as the nucleation surface 4. In addition to finely patterning the thin film in this way, as shown in FIG. 2 may be stacked to form a non-nucleation surface 3, and a fine window may be opened by etching to expose the nucleation surface 4. As shown in FIG. The nucleation surface 4 may be exposed by opening a fine window at the bottom of the recess (in this case, crystals are formed within the recess).

Furthermore, as shown in FIG. 1 (1) to (J), leaving a fine area and covering the rest with resist 7, ions (As, P,
The ion implantation region 8 with a high nucleation density may be formed by implanting ions (Ga, AI, In, etc.) into the thin film 2 made of a material with a low nucleation density. (Figure 1 (B)) (C): On the substrate thus obtained, a 11-V group compound (e.g. GaAs, GaAl
As.

GaP, GaAsP, InP, GaInAsP)
A crystal nucleus 9 is generated. At this initial stage of nucleation (while the base area of the generated nucleus is smaller than the nucleation surface), the concentration of the raw material is kept low (the molar ratio of the raw material containing atoms of group ■■ of the periodic table to the hydrogen gas for dilution). is preferably 1.5×10
1 or less, more preferably 1. OX 10-' or less, optimally about 8 X to-', lower limit is lXl0-'
degree) suppresses the uncontrolled generation of nuclei on the nucleation surface.

The V/IH molar ratio is 30 to 50 when the V group raw material is a gas.
When the group V raw material is a liquid, the growth is performed by setting an arbitrary value of about 20 to 30. Pressure is 80~1ootorr
(Fig. 1(C)) (D): m-v in which the III-V group compound crystal nucleus 9 has grown.
When the group compound single crystal 10 grows larger than the area of the nucleation surface 4 (crystal growth stage), the raw material concentration is higher than the initial stage of nucleation (group III of the periodic table for diluting hydrogen gas). The molar ratio of raw materials containing atoms is preferably 3 x 10-' or less, more preferably 2.5
X 10-' or less, optimally about 2 x 104, lower limit about 2 x 10-') to increase the crystal growth rate. (FIG. 1(D)) (E): The IIT-V group compound crystal grows around the nucleus, and the crystal grows laterally on the non-nucleation surface.

As described above, the adhesion coefficients of atoms of the crystal material on each of the crystal surface, nucleation surface, and non-nucleation surface are expressed as x, y, and z, respectively, as follows.

x>y>z At the initial stage of nucleation, the only exposed surfaces for the atoms of the crystalline material are the non-nucleation surface and the nucleation surface. Therefore, nuclei are selectively formed on the nucleation surface. Next, when the nuclei grow and cover the nucleation surface, only the crystal surface and non-nucleation surface exist, so the selectivity of nucleation becomes even higher. As the crystal grows and its surface area increases, it becomes more selective, so that uncontrolled nucleation on non-nucleating surfaces becomes less likely, meaning that the conditions that maintain selectivity gradually change as the crystal grows. .

Therefore, it is also preferable to continuously change V/III, which is a manufacturing condition that controls selectivity.

Optimal deposition conditions also vary depending on the arrangement and density of the nucleation surface on the non-nucleation surface. (Figure 1 (E
)) [Examples] The present invention will be explained below using Examples.

Example 1 FIGS. 2(A) to 2(F) show that GaAs was produced by the method of the present invention.
A schematic process diagram for forming crystals is shown.

(A) TaJ was deposited on the diquartz substrate 11 by vacuum evaporation method.
A total of 1,200 S films were deposited. The evaporation conditions were: the substrate temperature was room temperature, the evaporation source was Taxes, and the 0□ gas was 4×10
-'torr was introduced, and the deposition rate was 1 person/see. (Fig. 2 (A)) (B) Amorphous SiNx film 13 is secondarily formed by plasma CVD method.
300 people deposited. The deposition conditions were a substrate temperature of 350°C, a reaction pressure of 0.2 torr, and a raw material gas of 5i84100cc.
, NHs 200cc. (Figure 2 (B)) (C
): The SiNx film 1 is patterned using photolithography and reactive ion etching.
3 was partially removed to create fine windows 14 of 2 μm square at intervals of 40 μm, and Ta2O was formed.

exposed. This portion becomes the nucleation surface 4 of GaAs. (Fig. 2 (C)) (D): Heat treatment is performed at 850°C for 10 minutes in an H atmosphere, and then the GaAs crystal nuclei 15 are removed by the MOCVD method.
Generated on aaO@.

Trimethyl gallium (TMG) and tertiary butyl arsenic (TBAs) were used as raw materials, and H2 was used as a diluent gas.

V/III molar ratio TBAs: TMG was 25, the molar ratio of TMG to H2 for dilution was 8 x 10-', the reaction pressure was 80 torr, and the substrate temperature was 670°C. (Fig. 2 (D)) (E): About 30 minutes after the start of growth, the GaAs single crystal 16 in which the GaAs crystal nucleus 15 has grown is Ta2O,
After filling the area of window 14, TMG for H2
The molar ratio of was changed to 2 x 10-'. (FIG. 2 (E)) (F); Furthermore, the GaAs single crystal 16 continued to grow, forming grain boundaries 17 with other GaAs single crystals, and stopped growing when the crystal diameter reached 40 μm. (Figure 2 (
F)) After flattening the surface by polishing, InSn
Electrodes were attached by vapor deposition and annealed at 500° C. in Ar. When Hall measurements were carried out using this, it was found that an n-type crystal with a Hall mobility of 3200 cm"/V-s (300 K) and a carrier concentration of 2.times.10"7 cm was obtained.

Example 2 FIGS. 3(A) to 3(F) show that GaAl
A schematic process diagram for forming an As crystal is shown.

(A): 1500 amorphous SiO□ films 22 were deposited on a silicon wafer 21 by the CVD method using SiH4 and 02. (FIG. 3(A)) (B): Next, the 5iOz film was masked with a photoresist 23 in a desired pattern having openings 24, and At ions 25 were implanted using an ion implanter. The implantation amount was I x 10"7 cm". (Figure 3 (
B)) The size of the ion implanted portion was 2 μm square, and the interval between the implanted portions was 30 μm.

(C): Stow surface 2 where Al ions are not implanted
6, the probability of crystal nucleation is low (and the probability of crystal nucleation is high in the Al ion implanted region 27), a nucleus is generated in the region 27 where the crystal grows and becomes a single crystal.

(Figure 3 (C)) (D):)1. Heat treatment was performed at 850° C. for 10 minutes in an atmosphere, and then GaAlAs crystal nuclei 28 were generated on the At ion implantation region 27 by MOCVD.

Trimethyl gallium (TMG), trimethyl aluminum (TMA), and arsine (AsH-) were used as raw materials, and 2 was used as a diluent gas. Each molar ratio TMG
: TMA : AsH, is 3 : 2 : 250
(V/III = 50), the molar ratio of group II raw material to H2 is 7 x 10-', and the reaction pressure is 80 torr.
, the substrate temperature was 700°C.

(Fig. 3 (D)) (E): Thirty minutes after the start of growth, the GaAlAs single crystal 29, in which the GaAlAs crystal nuclei 28 have grown, covers the Al implanted region 15. While keeping the same, the molar ratio of Group II raw material to H2 is 2 X 1
The setting was changed to 0-'. (Figure 3 (E)) (F): Growth continued until the GaAlAs crystals collided with each other. 30 is a grain boundary.

(Figure 3 (F)) [Effects of the Invention] According to the crystal growth method of the present invention, nucleation on non-nucleation surfaces is prevented in the initial stage of nucleation, and single nuclei are generated only on nucleation surfaces. However, in the crystal growth stage, it becomes possible to increase the raw material concentration and efficiently obtain a high-quality single crystal of the III-V group compound at a higher growth rate.

[Brief explanation of the drawing]

Fig. 1 is a schematic process diagram showing the method of forming a crystal of the present invention, Fig. 2 is a schematic process diagram when the method of the present invention is used to form a GaAs crystal, and Fig. 3 is a schematic process diagram showing the method of the present invention for forming a GaAlAs crystal. FIG. 4 is a diagram showing the relationship between the nucleation density and the raw material gas concentration. l... Base material 2... Thin film made of a material with low nucleation density 3... Non-nucleation surface 4... Nucleation surface 5... Support body 6 made of material with low nucleation density... - Thin film made of material with high nucleation density 7... Photoresist 8... Ion implantation region 9... m-v group compound crystal nucleus lO... m-v group compound single crystal 11... Quartz substrate 12...Ta-0s film 1
3...SiNx film 1461. Window 15...
GaAs crystal nucleus 16...GaAs single crystal 17.
...Grain boundary 21...Silicon wafer 22.
...Amorphous SiO□ film 23...Photoresist 2
4... Opening 25... At ion 26.
...Region 27 where Al ions are not implanted...A1
Ion implantation region 28 --- GaAlAs crystal nucleus 29- GaAl
As single crystal 30...grain boundary

Claims (1)

[Claims] 1. A method for forming a crystal of a III-V compound using an organometallic chemical transport method, which includes a non-nucleation surface with a low nucleation density and a nucleation density higher than the nucleation density of the non-nucleation surface. At the initial stage of nucleation, the concentration of the raw material gas is reduced to 1. A method for forming a crystal, characterized by performing a crystal growth process in which the concentration of a source gas is lowered and the concentration of a source gas is higher in the crystal growth stage than in the initial stage of nucleation. 2. The molar ratio of the raw material containing Group III atoms of the periodic table to the diluting hydrogen gas at the initial stage of nucleation is 1.
The method for forming a crystal according to claim 1, wherein the crystal size is 5×10^-^5 or less. 3. The molar ratio of the raw material containing Group III atoms of the periodic table to the hydrogen gas for dilution in the crystal growth stage is 3×1.
2. The method for forming a crystal according to claim 1, wherein the crystal diameter is 0^-^5 or less. 4. The molar ratio (V/III) of Group V atoms to Group III atoms of the raw material containing Group V atoms of the periodic table and the raw material containing Group III atoms of the periodic table in the raw material gas is The method for forming a crystal according to claim 1, wherein the crystal size is 20 or more and 50 or less. 5. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed inside the non-nucleation surface. 6. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed on the non-nucleation surface. 7. The method for forming a crystal according to claim 1, wherein the nucleation surface is divided into a plurality of sections. 8. The method for forming a crystal according to claim 1, wherein the nucleation surface is regularly partitioned to form a plurality of them. 9. The method for forming a crystal according to claim 1, wherein the nucleation surface is irregularly partitioned to form a plurality of them. 10. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed in a lattice shape. 11. The method for forming a crystal according to claim 1, wherein a plurality of the nucleation surfaces are divided and provided, and a single crystal is grown from each of the nucleation surfaces. 12. The method for forming a crystal according to claim 1, wherein the single crystals grown from each nucleation surface are grown to adjacent sizes between adjacent nucleation surfaces. 13. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed by an ion implantation method. 14. Claim 1, wherein the surface of the substrate is made of non-single crystal material.
Method of forming the described crystals. 15. The material forming the non-nucleation surface is amorphous SiO_
2. The method for forming a crystal according to claim 1. 16. The method for forming a crystal according to claim 1, wherein the III-V group compound is a binary III-V group compound. 17. The method for forming a crystal according to claim 1, wherein the III-V group compound is a mixed crystal III-V group compound. 18. Claim 1, wherein the crystal formation treatment is an MOCVD method.
Method of forming the described crystals.