JPH03132016A - Method of forming crystal - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] [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 a III-V group compound single crystal or a III-V group compound polycrystal with controlled particle size.

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 SL, 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.

In this way, it can be seen that the conventional method of forming a single crystal thin film by epitaxial growth is highly dependent on the substrate material.Mathews et al.
GROWTH, Academic Press, Ne
w York.

1975 ed. by J.W. Mathews).

Furthermore, the size of the substrate is currently about 6 inches for Si wafers, and the increase in the size of GaAs and sapphire substrates is even slower. 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 depositing a thin film on an amorphous insulating substrate such as SiO□, 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, and a polycrystalline film is one that has a specific crystal orientation. It is a collection of single crystal grains separated 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, Journal of
Crystal Growth vol.

63, No, 3.0ctober 1983 edi
ted by G, W.

Cullen).

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・sec for amorphous silicon,
1-10 cm for polycrystalline silicon with a grain size of several hundred
”/V-sec, large-grain polycrystalline silicon 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, III-V compound semiconductors can be used for ultra-high-speed devices,
III-V is expected to be a material that can realize new devices such as optical devices that cannot be realized with SL.
Group compound crystals have so far been produced on Si single crystals or III
It can only be grown on single crystals of -V group compounds, which has been a major obstacle in device fabrication.

In order to solve the above-mentioned conventional problems, the present inventor has proposed that the nucleation density is sufficiently higher than that of the non-nucleation surface material on a non-nucleation surface with a low nucleation density, and is sufficient to the extent that only a single nucleus grows. We proposed a formation method in which a fine nucleation surface is provided and a crystal is formed by continuing growth centered on a single nucleus grown on the nucleation surface. It was shown that single crystal formation of the compound is possible.

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.

On the other hand, GaAs single crystal substrate and 5102+ 5INXI
Many studies have been reported on the selective growth of GaAs single crystals using mask materials such as WSIX. Among them, the molar ratio of group ■ and group ■ raw materials and the GaA on the mask
Regarding the relationship between precipitation of polycrystalline grains, T, HAGA, K,
Former RUMA et al.
．． It is reported in p. 29). According to it, GaA
In the system using Sing and WSix masks for the S single crystal, when the V/III molar ratio of the raw material is large, nucleation of GaAs polycrystalline grains is observed on the WsL mask, and the V/In ratio is large. When the molar ratio is small, Si
Nucleation of GaAs polycrystalline grains is observed on the O□ mask. However, the above report did not describe the influence or effect of varying the V/I molar ratio during crystal growth.

[Problems to be Solved by the Invention] However, the above method of forming crystals by providing a fine nucleation surface on a non-nucleation surface is not suitable for controlling nucleation on a fine nucleation surface by the MOCVD method. There were also some inadequacies, and problems such as nucleation occurring on the non-nucleation surface or no nucleation occurring on the nucleation surface occurred.

Therefore, the inventor's objective is to suppress the uncontrolled generation of nuclei on non-nucleation surfaces and to produce high-quality III-V compound monomers by setting growth conditions that are suitable for the initial stage of nucleation and the stage of crystal growth. The objective is to provide a method for growing crystals.

[Means for Solving the Problems] In order to solve the above problems, in a method for forming a crystal of a group III-V compound by an organometallic chemical transport method, a non-nucleation surface with a low nucleation density, and a non-nucleation surface of the non-nucleation surface are provided. A substrate having a free surface adjacent to a nucleation surface having a nucleation density greater than the nucleation density of At the initial stage of nucleation, the ratio V/III of Group V atoms to Group III atoms of the periodic table in the raw material gas is made high, and at the crystal growth stage, the ratio V/Ill is lowered (lower than the initial stage of nucleation). A method for forming a crystal is provided, which comprises performing a crystal growth treatment.

The crystal formation method 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, the nucleation surface, and the 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, the ratio V/In of the group ■ and group Ill raw materials is increased in order to increase the selectivity of nucleation. . Then, the stage where nucleation on the nucleation surface is completed and lateral growth begins on the non-nucleation surface (crystal growth stage)
When this happens, V/m is lowered to allow crystal growth.

Next, the generation of crystal nuclei on the non-nucleation surface and V/111
The relationship between molar ratios will be explained.

FIG. 4 shows the relationship between the density of GaAs crystal nuclei generated on various films and the V/111 molar ratio.

Growth conditions Trimethylgallium (TMG) Arsine (AsH-) Reaction pressure 80 torr Substrate temperature 640°C Growth time 5 minutes As is clear from Figure 4, materials with high nucleation density (e.g. AlaOs, Ta20g) have a V/111 molar ratio. Although the change in nucleation density is small even if
Materials with low nucleation density (e.g. SiO□, 313N4
) has a strong correlation between the V/111 molar ratio and the nucleation density. Especially in the region of high V/III molar ratio, A1
．． 0. .

The difference in nucleation density between Ta=Os, 5iOa, and 5isN4 is quite large, indicating that good selectivity can be obtained.

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

FIGS. 1(A) to 1(E) are schematic process diagrams for growing single crystals of group 1-v compounds by selective nucleation according to the method of the present invention.

(A): Base material 1 (for example, A1□03.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, amorphous, polycrystalline, non-single-crystalline Sin, 5ixN4, etc.) is deposited on the non-nucleation surface 3. A method such as a CVD method, a sputtering method, a vapor deposition method, or a coating method using a dispersion medium is used to form this thin film. Also,
As shown in FIG. 1(F), the support 5 made of the material with low nucleation density may be used without using the base material 1 ((first
Figures (A)) (B): Materials with higher nucleation density than non-nucleation surfaces (non-single crystal Al2O3, AIN, Taxes,
Ti0z, WO2, etc.) is grown 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 this is used as the nucleation surface 4. In addition to finely patterning the thin film in this way, as shown in FIG. 2 are stacked to form a non-nucleation surface 3, and fine windows are opened by etching to form a nucleation surface 4.
Alternatively, as shown in FIG. 1 (H), a recess is formed in the thin film 2 made of a material with a low nucleation density, and a minute window is opened at the bottom of the recess to expose the nucleation surface 4. (in this case, crystals are formed within the recess).

Furthermore, as shown in FIG. 1 (I) to (T), leaving a fine region 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, Al, 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 III-V compound (e.g. GaAs, GaA
lAs.

GaP, GaAsP, InP, GaInAsP) crystal nuclei 9 are generated. At this early stage of nucleation (while the basal area of the generated nucleus is smaller than the nucleation surface), V/1
11 molar ratio should be high (i. If the raw material is a liquid organic raw material, preferably 10 or more, more preferably 20 or more, optimally 30 or more; if the raw material is a gaseous raw material, preferably 30 or more,
(more preferably 45 or more, optimally 60 or more) to suppress the occurrence of defects due to the deficiency of group (II) atoms. (Figure 1(C)) (D): III-V compound crystal nucleus 9 has grown
- When the group V compound single crystal IO grows to expand beyond the area of the nucleation surface 4 (crystal growth stage), V/
The 111 molar ratio is lower than the value of V/II+ at the initial stage of nucleation (if group V is a liquid organic raw material, preferably 5 or more, more preferably 7 or more, optimally 15 or more; in the case of a gaseous raw material, Preferably 20 or more, more preferably 3
5 or more, optimally 40 or more. ) Change the settings to make efficient use of the V-kneading material and avoid wasting it. (1st
Figures (D)) and (E): Group III-V compound crystals grow around the nucleus, and the crystals grow laterally on the non-nucleation surface.

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

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. Subsequently, when the nucleus grows and completely covers the nucleation surface, only the crystal surface and non-nucleation surface exist, and the selectivity of nucleation becomes even higher. Furthermore, as the crystal grows and its surface area increases, the selectivity becomes even higher, so that uncontrolled nucleation on non-nucleating surfaces becomes almost impossible (i.e., the conditions for maintaining selectivity are It changes gradually over time.

Therefore, it is also preferable to continuously change the production conditions (1)/III which control the 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) Ta2 is deposited on the diquartz substrate 11 by vacuum evaporation method.
's film 12 was deposited by 1,500 people. The evaporation conditions were: the substrate temperature was room temperature, the evaporation source was Ta2es, and the O□ gas was 4×1.
It was introduced down to 0-'torr, 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 5iH4100cc.
, 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 60 μm intervals to expose Ta at 0°. This portion becomes the nucleation surface 4 of GaAs. (Fig. 2 (C)) (D): Heat treatment was performed at 850°C for 10 minutes in an H atmosphere, and then the GaAs crystal nuclei 15 were removed by the MOCVD method.
was generated on agOs.

Trimethyl gallium (TMG) and tertiary butyl arsine (TBAs) were used as raw materials, and H2 was used as a diluent gas. The molar ratio of raw material gases TMG:TBAs was 1:35, the reaction pressure was 80 torr, and the substrate temperature was 670°C.

(Fig. 2 (D)) (E): About 10 minutes after the start of growth, when the GaAs single crystal 16 in which the GaAs crystal nucleus 15 had grown filled the region of the Ta1ls window 14, the reaction pressure was increased to 150 torr. The ratio of TMG and TBAs was changed to 1=20.

(Figure 2 (E)) (F): As the GaAs single crystal 16 continues to grow, it forms grain boundaries 17 with other GaAs single crystals, and the crystal diameter becomes 60 μm.
It stopped growing when it reached m. (FIG. 2(F)) After the surface was flattened by polishing, an InSn electrode was attached by vapor deposition, and annealing was performed at 500° C. in Ar. When Hall measurements were performed using this, the Hall mobility was 24
00cm”/Vs (300K), carrier concentration 8
It was found that an n-type crystal of X 10"70m" 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): 1,500 amorphous SiO□ films 22 were deposited on a silicon wafer 21 by the CVD method using 5IH4 and 02. (Fig. 3 (A)) (B) Second, the SiO□ film was masked with a photoresist 23 into a desired pattern having openings 24, and AI ions 25 were implanted using an ion implanter. The amount is 1xlO1'/cffl! Met. (FIG. 3(B)) The size of the ion implantation portion was 2 μm square, and the interval between the implantation portions was 30 μm.

(C): SiO□ surface 2 where At ions are not implanted
The probability of crystal nucleation is low in A1 ion implantation region 27, and the probability of crystal nucleation is high in A1 ion implantation region 27, in which a nucleus grows into a single crystal.

(Fig. 3 (C)) (D): Heat treatment is performed at 850°C for 10 minutes in an H atmosphere, and then by MOCVD method, Al generates GaAlAs crystal nuclei 28 on the ion implantation region 27. I let it happen.

Trimethylgallium (TMG), trimethylaluminum (TMA), and arsine (Ashs) were used as raw materials, and H2 was used as a diluent gas. The molar ratio of raw material gas is TM
G:TMA:ASH3 is 3:2:30
0 (V/III=60), the pressure is 80 torr,
The substrate temperature was 700°C.

(Fig. 3 (D)) (E): When the GaAlAs single crystal 29 in which the GaAlAs crystal nuclei 28 have grown completely covers the Al implantation region 15 15 minutes after the start of growth, the molar ratio of the raw materials is changed to TMG.
: TMA : AsHs = 3 : 2 : 225
The setting was changed to (V/III = 45). (3rd
Figure (E)) (F): Growth continued until the GaAIAS 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, a controlled single crystal of the ■-V group compound can be grown on the nucleation surface, and at each growth stage, By setting an appropriate V/m molar ratio, V
No need to use excess group raw materials (efficiently, high quality II)
It becomes possible to obtain a single crystal of a group IV compound.

[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 nucleation density and V/m molar ratio. 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... nl -V group compound crystal nucleus lO... Arch n-V group compound single crystal 11... Quartz substrate 12...Taxes film 1
3...SiN, film 14...Window 15...
GaAs crystal nucleus 16...GaAs single crystal 17.
...Grain boundary 21...Silicon wafer 22.
...Amorphous 5iOi film 23...Photoresist 2
4... Opening 25... A1 ion 26.
...Region 27 where Al ions are not implanted...At
Ion implantation region 2B---GaAlAs crystal nucleus 29---GaAlAs 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. In the initial stage of nucleation, the substrate has a free surface adjacent to a nucleation surface having a small enough area to form a unique nucleus that grows into a single crystal. Ratio of Group V atoms to Group III atoms of the periodic table V/II
1. A method for forming a crystal, which comprises performing a crystal growth process in which I is increased and the ratio V/III is lowered in the crystal growth stage than in the initial stage of nucleation. 2. The method for forming a crystal according to claim 1, wherein the ratio V/III of the group V atoms to the group III atoms of the periodic table in the initial stage of nucleation is 10 or more. 3. Claim 1, wherein the ratio V/III of the group V atoms to the group III atoms of the periodic table in the crystal growth stage is 5 or more.
Method of forming the described crystals. 4. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed inside the non-nucleation surface. 5. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed on the non-nucleation surface. 6. The method for forming a crystal according to claim 1, wherein the nucleation surface is divided into a plurality of sections. 7. The method for forming a crystal according to claim 1, wherein the nucleation surface is regularly partitioned to form a plurality of them. 8. The method for forming a crystal according to claim 1, wherein the nucleation surface is irregularly partitioned to form a plurality of them. 9. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed in a lattice shape. 10. 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. 11. 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. 12. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed by an ion implantation method. 13. Claim 1, wherein the surface of the substrate is made of non-single crystal material.
Method of forming the described crystals. 14. The material forming the non-nucleation surface is amorphous SiO_
2. The method for forming a crystal according to claim 1. 15. The method for forming a crystal according to claim 1, wherein the III-V group compound is a binary III-V group compound. 16. The method for forming a crystal according to claim 1, wherein the III-V group compound is a mixed crystal III-V group compound. 17. Claim 1, wherein the crystal formation treatment is an MOCVD method.
Method of forming the described crystals.