JPH03132015A - Method of forming crystal - Google Patents

Abstract

PURPOSE:To obtain a high quality III-V compound single crystal without using excessive V-group material by a method wherein creation of uncontrollable seeds on a non-seed-forming surface is suppressed. CONSTITUTION:A thin film 2 made of material whose crystal seed forming density is low (for instance non-single-crystalline SiO2) is deposited by a CVD method. Non-single-crystalline Al2O3 layers 4 which have a higher seed forming density than a non-seed-forming 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. III-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 not 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. The III-V compound crystals are made to grow horizontally onto the non-seed-forming surface 3 with the seeds as the centers of growth.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an Nr-V group compound crystal and a method for forming the same, and in particular, to a crystal of an Nr-V group compound and a method for forming the same. 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 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 JJ, Mathews).

Furthermore, the size of the substrate is currently about 6 inches for St wafers, and the increase in the size of GaAs and 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, the conventional method has had the problem that the type of substrate material is limited to an extremely narrow range in order to form a single crystal counterfeit from which a high-quality device can be manufactured.

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 insulator substrate, such as 5ins, 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 Si on SiO□ by the CVD method, if the deposition temperature is about 600°C or less, it will become amorphous silicon, and if the temperature is higher than that, the grain size will be in the range of several hundred to 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 (Singlecrystal 5i).
licon on non-single-cryst
alinsulators, JouIIIal of
Crystal Growth vol.

63, No, 3. 0ctober 1983
Edited 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”/■・sec for amorphous silicon
, for polycrystalline silicon with a grain size of several hundred 1”−1
0 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. Therefore, its performance is poor (inferior).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 are expected to be materials that can realize new devices that cannot be realized with Si, such as ultra-high-speed devices and optical devices.
Group V compound crystals have so far been SL single crystal islands or II
It can only be grown on single crystals of I-V 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.

[Problems to be Solved by the Invention] However, the above-mentioned invention does not solve the problem of crystal defects caused by the deficiency of group Ⅰ elements in a low-pressure atmosphere that is advantageous for generating nuclei only on fine nucleation surfaces in the MOCVD method. In order to suppress the occurrence of group V raw materials, it was necessary to supply a very large amount of group V raw materials compared to group III raw materials, which sometimes caused the problem that the amount of group V raw materials supplied was enormous. If the pressure of the reaction atmosphere is increased in the initial stage of nucleation, a problem may arise in that uncontrolled nuclei are generated on non-nucleation surfaces other than the fine nucleation surfaces.

Therefore, an object of the present invention is to provide a method for growing single crystals of group V compounds by suppressing the uncontrolled generation of nuclei on non-nucleation surfaces and further increasing the utilization rate of group V raw materials.

[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 an organometallic chemical transport method, a non-nucleation surface with a low nucleation density and a 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 reaction pressure is low and the ratio of Group II atoms to Group I II atoms of the periodic table in the raw material gas is reduced to V/III.
A method for forming a crystal is provided, which is characterized in that a crystal growth process is performed in which the reaction pressure is higher in the crystal growth stage than in the initial stage of nucleation and the ratio V/III is lower than in the initial stage of nucleation.

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 reaction pressure is set low to increase the selectivity of nucleation, and the ratio of Group I and Group III raw materials is adjusted. Increase V/+n. Then, when nucleation on the nucleation surface is completed and lateral growth on the non-nucleation surface begins (crystal growth stage), the reaction pressure is increased and V/III is lowered to stop crystal growth. It is something that makes you

Next, the relationship between crystal nucleation on the nucleation surface and reaction pressure will be explained.

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

Growth conditions Nitrimethylgallium (TMG) Tertiary butylarsine (TBAs) Ratio of group V and group III raw materials [molar ratio] (V/III) 5 Substrate temperature 670°C Growth time 5 minutes As is clear from Figure 4, Ga
Generate As crystal nuclei and place them on the non-nucleation surface (for example, 5to
It can be seen that in order to increase the selectivity of not generating nuclei at 2.5iJL), the reaction pressure can be lowered.

The relationship between the reaction pressure and the electrical properties of the GaAs film will be explained.

FIG. 5 shows the relationship between reaction pressure and Hall mobility. Growth conditions: TMG TBAs V/III 15 Substrate temperature 670°C As is clear from Figure 5, as the reaction pressure decreases, the electron mobility decreases, and a reversal from n-type to p-type conduction occurs at around 10 torr. ing. This is thought to be because defects occur due to As deficiency in the growing GaAs crystal as the absolute pressure of As in the reaction gas decreases.

In order to prevent this reversal, it is desirable to further increase the amount of As supplied relative to Ga.

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 a single crystal of an IU-V compound by performing selective nucleation according to the method of the present invention.

(A) Two base materials (e.g. Al2O, 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 crystal SiO□, 5ixN4, etc.) is deposited on top of a high melting point metal (such as a high melting point metal such as metal) to form a 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. Further, 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 (((A) in FIG. 1)(B): Non-nucleation surface Materials with higher nucleation density (non-single crystalline AIJi, AIN, Taxes
, Ti0z, WOz, etc.) to form a sufficiently small area (preferably 10 μm square or less, optimally 2 μm square or less) to form a single nucleus to form a single crystal, 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 FIGS. 1(I) to (J), leaving a fine area and covering the rest with resist 7, ions (As, P,
Ga, AI, III, etc.) may be implanted into the thin film 2 made of a material with a low nucleation density to form the ion implantation region 8 with a high nucleation density. (FIG. 1(B)) (C): Group III-V compound crystal nuclei 9 are generated on the substrate thus obtained by MOCVD.

At this initial stage of nucleation (while the base area of the generated nuclei is smaller than the nucleation surface), the reaction pressure is low (preferably 30
torr, more preferably below 10 torr, optimally below 5 torr) to prevent uncontrolled nucleation on non-nucleating surfaces. At this time, the lower limit of the reaction pressure is preferably 10-'torr, more preferably 1
0-'' torr, optimally 0.1 torr is desirable.

In addition, the value of V/III should be high (if the V group raw material is a liquid organic raw material, preferably 10 or more, more preferably 2
0 or more, optimally 25 or more; in the case of gas raw materials, preferably 30 or more, more preferably 35 or more, optimally 45 or more) to suppress the occurrence of defects due to the deficiency of group V atoms. (1st
Figure (C)) (D): III-V compound crystal nucleus 9 has grown
- When the group V compound single crystal 10 grows to expand beyond the area of the nucleation surface 4 (crystal growth stage), the reaction pressure is set higher than the reaction pressure at the initial stage of nucleation (preferably 30 torr or more, More preferably 40tor
r or more, optimally 50 torr or more. At this time,
In order to ensure safety, the upper limit of the reaction pressure is preferably atmospheric pressure. ). At the same time, the value of V/Ill is lower than the value of V/III 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 12 or more; gas In the case of raw materials, the number is preferably 20 or more, more preferably 25 or more, and optimally 28 or more.) Change the settings to efficiently utilize group V raw materials and avoid wasteful consumption. (Figure 1 (D)) (E): Proceeding the growth of ■-V group compound crystals centering on the nucleus,
Crystals are grown laterally onto non-nucleated surfaces (.

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 denoted 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. Next, the nucleus grows and covers the nucleation surface (then only the crystal surface and non-nucleation surface exist, so the selectivity of nucleation becomes even higher.The crystal grows further). As the surface area increases, the selectivity becomes even higher, so that uncontrolled nucleation on non-nucleating surfaces becomes less likely, meaning that the conditions that maintain selectivity change gradually as the crystal grows.

Therefore, it is also preferable to continuously change the reaction pressure and V/III, which are the production conditions that control 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 quartz substrate 11 by vacuum evaporation method.
A film 12 was deposited by 1500 people. The evaporation conditions were as follows: the substrate temperature was room temperature, the evaporation source was Ta2Og, and the 0□ gas was 4×10
-'torr, and the deposition rate was 1 person/sec. (Fig. 2 (A)) (B) - Next, the amorphous SiNx film 13 is
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 Ta1ls. This portion becomes the nucleation surface 4 of GaAs. (FIG. 2(C)) (D): 1 was heat-treated in an atmosphere at 850° C. for 10 minutes, and then GaAs crystal nuclei 15 were generated on Ta5Os by MOCVD.

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 1:25, the reaction pressure was 3 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=12.

(Figure 2 (E)) (F); Furthermore, the GaAs single crystal 16 continues to grow, forming grain boundaries 17 with other GaAs single crystals, and the crystal diameter becomes 60 μm.
It stopped growing when it reached m. (Figure 2 (F)) Next, after flattening the surface by polishing, a IIISn electrode was attached and hole measurements were performed.
cm''/V-s (300K), carrier concentration 5
It was found that an n-type crystal of X 1016/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 5iOa films 22 were deposited on a silicon wafer 21 by the CVD method using SiH4 and 0□. (FIG. 3(A)) (B): Next, the SiO□ film was masked with a photoresist 23 in a desired pattern having openings 24, and A1 ions 25 were implanted using an ion implanter. The implantation amount was I x 10”7cm2 (Fig. 3 (
B)) The size of the ion implanted portion was 2 μm square, and the interval between the implanted portions was 30 μm.

(C): SiO□ surface 2 where Al ions are not implanted
6, the probability of crystal nucleation is low, whereas the probability of crystal nucleation is high in the Al ion implantation region 27, and a nucleus is generated in the region 27 where the crystal grows to become 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, At 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 T
MG: TMA: AsHs is 3:2:
250 (V/1'1l=50) and the pressure is 3t
orr, and the substrate temperature was 700°C.

(Fig. 3 (D)) (E): 15 minutes after the start of growth, the GaAlAs single crystal 29 in which the GaAlAs crystal nucleus 28 has grown covers the At implantation region 15 (at this point, the reaction pressure is increased to 200 torr).
molar ratio of raw materials TMG:TMA:A
sH,=3:2:175 (V/III=3
The settings were changed to 5). (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, uncontrolled generation of nuclei on non-nucleation surfaces can be suppressed, and unnecessary use of Group V raw materials can be avoided ( It becomes possible to efficiently grow a single crystal of a high-quality m-v group 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 reaction pressure, and Fig. 5 is a schematic process diagram when used for the formation of GaAs holes (
FIG. 2 is a diagram showing the relationship between Hall (Hall) mobility and reaction pressure. 1... 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 7 made of material with high nucleation density...Photoresist 8...Ion implantation region 9...III-V group compound crystal nucleus IO...II-V group compound single crystal 11... Quartz substrate 12...Tag's film 1
3...SiNx film 14...Window 15...
・GaAs crystal nucleus 16...GaAs single crystal 17
... Grain boundary 21 ... Silicon wafer 22
...Amorphous 5i02 film 23...Photoresist 24...Opening 25...AI ion 26
...Region 27 where At ions are not implanted...A
t ion implantation region 2g...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. At the initial stage of nucleation, a low reaction pressure is applied to the substrate, which 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. The ratio V/III of Group V atoms to Group III atoms of the periodic table in the raw material gas is made higher, and the reaction pressure is made higher in the crystal growth stage than in the early stage of nucleation, so that the ratio V/III is higher than that in the early stage of nucleation. A method for forming a crystal, characterized by performing a crystal growth treatment to lower the crystal. 2. The reaction pressure at the initial stage of nucleation is 30t.
2. The method for forming a crystal according to claim 1, wherein the crystal growth rate is less than orr. 3. 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. 4. The reaction pressure in the crystal growth stage is 30 to
2. The method for forming a crystal according to claim 1, wherein the crystal diameter is rr or more. 5. 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. 6. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed inside the non-nucleation surface. 7. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed on the non-nucleation surface. 8. The method for forming a crystal according to claim 1, wherein the nucleation surface is divided into a plurality of sections. 9. The method for forming a crystal according to claim 1, wherein the nucleation surface is regularly partitioned to form a plurality of them. 10. The method for forming a crystal according to claim 1, wherein the nucleation surface is irregularly partitioned to form a plurality of them. 11. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed in a lattice shape. 12. 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. 13. 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. 14. The method for forming a crystal according to claim 1, wherein the nucleation surface is formed by an ion implantation method. 15. Claim 1, wherein the surface of the substrate is made of non-single crystal material.
Method of forming the described crystals. 16. The material forming the non-nucleation surface is amorphous SiO_
2. The method for forming a crystal according to claim 1. 17. The method for forming a crystal according to claim 1, wherein the III-V group compound is a binary III-V group compound. 18. The method for forming a crystal according to claim 1, wherein the III-V group compound is a mixed crystal III-V group compound. 19. Claim 1, wherein the crystal formation treatment is an MOCVD method.
Method of forming the described crystals.