JPH1135389A - Crystal growth method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of growing a long-sized single crystal of a ternary or more compd. SOLUTION: A layer of a seed crystal 11, a first material layer 12 which is adjacent to this seed crystal layer and has the m.p. lower than the m.p. of the seed crystal and a second material layer 13 which is adjacent to this first material layer 12, has the m.p. higher than the m.p. of the first material layer and is formed by coating the whole or part of the surface exclusive of the part in contact with the first material layer with a material having the poor wettability with the melt of the first material or the soln. of the second material in the first material are arranged in this order. These layers are housed into a vessel which is then put into a heating atmosphere where the crystal of the compd. consisting of the constituting elements of the first material layer and the second material layer is grown on the surface of the seed crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for growing a crystal, and more particularly to a method for growing a ternary compound crystal. 2. Description of the Related Art Today, electronic devices and optical devices that utilize the functions of crystals such as semiconductors, oxides, and metals are widely used. In particular, compound semiconductors and their mixed crystals can be changed by changing the composition.
Characteristics such as energy gap, refractive index, mobility, and lattice constant change.
Widely used as light emitting elements and optical elements.

At present, these devices are manufactured by using a binary compound crystal as a substrate and growing a binary or more compound semiconductor thereon. By the way, in this case, the lattice constant of the grown crystal becomes a problem. When there is a difference between the substrate crystal and the lattice constant, crystal defects are introduced into the grown crystal, and a high-performance device cannot be realized. Therefore,
At present, a ternary or quaternary mixed crystal that is lattice-matched with a binary substrate crystal is grown. For this reason, even if an element is designed to improve the efficiency and speed up the crystal growth, the lattice constant must be matched with the substrate crystal, and the optimization cannot be performed.

[0003] It is a compound semiconductor substrate of three or more elements that can solve the above inconveniences and optimize the element characteristics. Since the lattice constant can be arbitrarily set by changing the composition, crystal growth with few defects can be performed, and a high-performance device can be realized.

[0004]

2. Description of the Related Art In the process of growing a compound semiconductor crystal of three or more elements from a melt or a solution, the distribution coefficient is not 1 (the composition in the liquid phase is different from the composition in the growing solid phase). The composition changes as the crystal grows, and the composition distribution in the growth direction in the grown crystal becomes a so-called normal freezing state, so that a ternary or higher compound semiconductor having a uniform composition distribution cannot be grown. Therefore, it is necessary to replenish a specific element that is depleted in the liquid phase by precipitation into the solid phase from the outside in the liquid phase according to the depleted amount. For example, in LEC (Liquid Sealed Pull) growth of InGaAs, a method is employed in which GaAs that is depleted during growth is supplied to the melt in the crucible.

As growth methods other than the LEC method, there are a temperature difference method and a zone method. In the temperature difference method, as shown in FIG. 1, a crystal growth material 4, a solution material 3 (low melting point metal), and a seed crystal 2 are sequentially and adjacently sealed in a crucible 1. From this state, the crucible is placed in a heating furnace and heated to obtain a temperature distribution as shown in the figure, and the boundary between seed crystal 2 and solution material 3 and its vicinity and the boundary between crystal growth material 4 and solution material 3 and its vicinity are formed. Upon dissolution, the solute concentration in the solution increases, and after a certain period of time, the solution is saturated. At this time, the heating temperature of the seed crystal is
Lower than its melting point. Since the solubility is higher when the temperature is higher, when a temperature gradient as shown in FIG. 1 is given, the concentration in the solution becomes higher on the crystal growth material side than on the seed crystal side,
Due to the concentration gradient, the solute diffuses and moves to the low temperature side,
Since the solution on the seed crystal side becomes supersaturated, crystals grow on the seed crystal. As a result, the solution on the side of the crystal growth material becomes unsaturated, and dissolution occurs on the surface of the crystal growth material. While maintaining the temperature gradient, growth on this seed crystal and dissolution of the crystal growth material continues. Further, if the heating furnace is moved to the crystal growth material side at the same speed as the growth speed to change the temperature distribution, the temperature at the growth interface becomes constant, so that the growth composition can be kept uniform. According to this temperature difference method, the element that precipitates on the seed crystal from the solution is supplied from the crystal growth material into the solution, so that the specific element is not depleted in the entire crystal growth material.

Next, the zone method will be described with reference to FIGS. 2 and 3 by taking crystal growth of an InGaAs compound semiconductor as an example. FIG. 2 is an InAs-GaAs quasi-binary phase diagram. As can be seen from this figure, in order to obtain an In _x Ga _{1 -x} As crystal of X = 0.05 (point a) by precipitation from a liquid phase, a liquid equilibrating with this solid phase at a temperature Ta, which is the melting point, is required. Since they must be phase compositions (point b), their composition values differ greatly. Therefore, as shown in FIG. 3, a crystal growth material 8 having a composition at point b equilibrated with the solid phase at point a (or an aggregate of two or more materials having a composition at point b on average) is used.
Under a temperature condition in which only the material 7 having the composition at the point b melts and the material 8 having the composition at the point a does not melt, a temperature gradient is given so that the seed crystal side is on the low temperature side, and the material has the composition at the point b. Crystal growth is performed on the seed crystal 6 from the melt of the material 7, and at the same time, the crystal growth material 8 having the composition at the point a disposed on the high temperature side is melted at the solid-liquid interface, and the raw material is supplied into the melt. . If the furnace is moved to the growth material side at the same speed as the growth speed during the growth, the growth and the melt supply are continued.

[0007]

However, when crystal growth is performed by the conventional temperature difference method or zone method as described above, after a single crystal is grown to a thickness of several mm from the interface with the seed crystal, The growth of a long single crystal was difficult due to the incorporation of subgrains and polycrystallization. Therefore, the present invention
An object of the present invention is to provide a method capable of growing a long single crystal of a compound having three or more elements.

[0008]

SUMMARY OF THE INVENTION The present invention therefore provides a seed crystal layer, a layer of a first material adjacent to the seed crystal layer, the first material having a lower melting point than the seed crystal, and the first crystal layer. Adjacent to the material layer, having a higher melting point than the first material layer, and
The whole or a part of the surface other than the portion in contact with the first material layer was coated with a material having poor wettability with the melt of the first material or the solution of the second material in the first material. The second material layer and the second material layer are arranged in this order, these are housed in a container, and then the container is placed in a heated atmosphere to remove the constituent elements of the first material layer and the second material layer. A crystal growth method comprising growing a crystal of the compound on the surface of the seed crystal.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, a solid phase of a predetermined material and a solution or a melt of the material are well wetted. The effect of wetting is significant under microgravity and the solution may surround the entire circumference of the solid phase. In the space experiments by the present inventors, the movement of the solution due to wetting was also observed.From this finding, the present inventors found that in crystal growth under microgravity, in order to prevent the movement of the solution, the solution was solidified with a material with poor wettability. A method for crystal growth by covering the surface of the phase was proposed (Japanese Patent Application No. Hei 1-20463).
0). However, in the case of crystal growth on the ground, it was thought that such a coating was unnecessary because the movement of the solution was restricted by gravity.

However, it has been found that one of the difficulties in growing a long single crystal by the temperature difference method or the zone method is the movement of the liquid phase due to wettability. The liquid phase moves to the high temperature side along the surface of the crystal growth material and dissolves the high temperature side of the crystal growth material. For this reason, as the crystal growth proceeds, the shape of the interface between the liquid phase and the crystal growth material deviates from a plane, the composition distribution in the liquid phase does not become constant, and instability appears in the crystal growth.

Therefore, in the present invention, all or a part of the surface of the crystal growth material layer other than the portion in contact with the melt portion or the solution portion is melted with the first material (that is, the solution material) or the first material. By coating the solution of the second material (ie, the crystal growth material) in the material (ie, the solution growth material) and the material having poor wettability, the shape of the melting surface or the melting surface of the crystal growth material is stably maintained, and It is intended to facilitate the growth of a long single crystal.

That is, in the present invention, in the temperature difference growth method and the zone growth method, the whole or a part of the outer periphery of the crystal growth material layer other than the portion in contact with the liquid phase is coated with a material having poor wettability with the liquid phase. I am trying to do it. Therefore, when the crystal grows on the seed crystal, the movement of the liquid phase along the surface of the crystal growth material can be prevented, so that the shape of the liquid phase can be kept stable, and the crystal growth is stabilized. In addition, the growth length of the single crystal can be increased.

In the present invention, preferably, a temperature gradient is applied to the heating atmosphere such that the seed crystal side is on the low temperature side, and the first material layer is melted into a melt, and the solute in the melt is melted. Utilizing the temperature dependence of the solubility of the compound material, the compound crystal is grown on the seed crystal, and the low-temperature side surface of the second material layer is dissolved in the melt. Or the first
A temperature gradient is applied to the heating atmosphere such that the seed crystal side is at a lower temperature side under a temperature condition in which the material of the second material melts and the entire second material does not melt, and the first material layer and the second material layer are formed on the surface of the seed crystal. Preferably, a solid phase of the compound composed of the molten element from the second material layer is formed, and the compound crystal is grown.

In any of the above cases, the seed crystal is III-
The first material comprises a compound of two or three elements selected from Group V elements, and the first material comprises a simple substance or a compound of one to three elements selected from Group III and Group V elements; Is selected from the group III-V elements
Or it is good to consist of a compound of three kinds of elements. In the present invention, as described above, the surface of the second material layer is a melt of the first material or the second material in the first material except for a portion in contact with the first material layer. And at the same time, all or a part of the surface of the seed crystal layer other than the portion in contact with the first material layer is a melt of the first material or the first material layer. It is more preferable that the material is coated with a solution of the seed crystal in the material described above and a material having poor wettability. The coating material for the second material layer and the seed crystal layer is preferably SiO ₂ , SiN or SiON.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the drawings. Example 1 FIG. 4 is a view for explaining a method of growing a ternary compound crystal by an improved zone growth method according to a first example of the present invention.

A p having an inner diameter of 15 mm, an outer diameter of 18 mm, and a length of 50 mm
5 mm thick GaAs single crystal (seed crystal) in BN crucible 10
11,2.5mm thick InAs (first material) 12 and CVD-SiO ₂ 1 a portion other than the portion in contact with the InAs
5 mm thick GaAs coated to a thickness of about 500 nm with
(Second material) 13 was added, and this was further added to an inner diameter of 19 mm.
It is vacuum-sealed in a quartz ampule 9 having an outer diameter of 22 mm at a degree of vacuum of 5 × 10 ⁻⁷ Torr or less. When this is heated in an electric furnace, InAs is melted at 942 ° C., and when the temperature is further raised, the GaAs surface in contact with the melt is melted and 1170
When the temperature is raised to ℃, the composition of the melt becomes In _0.37 Ga _0.63 As
(Point b in FIG. 2). The melting reduces the thickness of the GaAs single crystal layer to 1.2 mm and the thickness of the GaAs material layer to 0.4 mm. Next, the temperature of the seed crystal-melt interface was set to 1170 ° C.
And a temperature gradient of 20 ° C./cm is formed, and the sample is moved at a speed of 3 μm / min in the direction of the arrow in the figure (at this time, the electric furnace may be moved in the direction opposite to the arrow). By maintaining this state and continuing crystal growth for 20 hours, In _x Ga _{1 -x} As having a diameter of 15 mm and a length of 3.6 mm was grown. The solid phase composition of InAs in the grown crystal gradually decreased from 0.05 to 0.048 from the growth interface to a thickness of 0.4 mm, but remained constant at 0.05 in the subsequent growth layer.

In the conventional method without coating with SiO ₂ , the same solid phase composition can be obtained.
Sub-grains began to be mixed from around mm, and polycrystallization was often observed. In this example, the entire growth length was a single crystal. Embodiment 2 As a second embodiment of the present invention, a method of growing a ternary compound crystal with an improved temperature difference growth method will be described with reference to FIG.

A p with an inner diameter of 15 mm, an outer diameter of 18 mm and a length of 50 mm
In the crucible 16 made of BN, CVD-
5 mm coated with SiO ₂ 18 to a thickness of about 500 nm
Seed crystal layer 17 made of thick In _0.1 Ga _0.9 As single crystal
And a first material layer 19 made of In _0.9 Ga _{0.1 having a} thickness of 2 mm and a portion other than a portion in contact with the In _0.9 Ga _0.1 layer were covered with CVD-SiO ₂ 21 to a thickness of about 500 nm. A second material layer made of In _0.1 Ga _0.9 As and having a thickness of 5 mm was put therein, and this was further coated with an inner diameter of 19 mm and an outer diameter of 2 mm.
A 2 mm quartz ampule 15 is vacuum-sealed at a degree of vacuum of 5 × 10 ⁻⁷ Torr or less. This is heated in an electric furnace having a temperature gradient shown in FIG. 5, the temperature at the interface between the seed crystal and the first material is set to 900 ° C., and the temperature gradient is set to 20 ° C./cm. By this heating, the first material portion is melted into a melt, and the seed crystal layer and the second material layer in contact with the melt are dissolved in the melt. Next, the sample was placed at 1 μm /
(The electric furnace may be moved in the direction opposite to the arrow at this time.) By maintaining this state and continuing crystal growth for 50 hours, In _0.1 Ga _0.9 As having a diameter of 15 mm and a length of 3 mm was grown.

In the conventional method without coating with SiO ₂ , the same solid-phase composition can be obtained, but subgrain starts to be mixed when the grown film thickness exceeds about 1.5 mm, and polycrystallization is often observed. However, in this example, the entire growth length was a single crystal.

[0020]

According to the present invention, the whole or part of the surface of the crystal growth material layer other than the portion in contact with the melt or solution is coated with a material that is poorly wet with the melt or solution. The shape of the melting surface or the melting surface of the material can be stably maintained, and the growth of a longer single crystal can be easily achieved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the principle of a temperature difference method according to a conventional technique.

FIG. 2 is an InAs-GaAs quasi-binary phase diagram.

FIG. 3 is a schematic diagram showing the principle of the zone method according to the related art.

FIG. 4 is a schematic view for explaining one embodiment of the method according to the present invention.

FIG. 5 is a schematic diagram for explaining another embodiment of the method according to the present invention.

[Explanation of symbols]

1, 5, 10, 16 ... crucible 2, 6, 11, 17 ... seed crystal 3, 7 ... solution material layer 4, 8 ... growth material layer 9, 15 ... quartz ampoule 12, 19 ... first material layer 13, 20: second material layer 14, 18, 21 ... coated SiO ₂ layer

Claims (7)

[Claims] 1. A seed crystal layer, a first material layer having a lower melting point than the seed crystal adjacent to the seed crystal layer, and a first material layer adjacent to the first material layer. The melting point of the first material layer is higher than that of the first material layer, and all or a part of the surface other than the portion in contact with the first material layer is melted of the first material or the second material in the first material. A solution of the material and a layer of a second material coated with a poorly wetted material are arranged in this order, these are housed in a container, and then the container is placed in a heated atmosphere and the first material layer And growing a crystal of a compound comprising a constituent element of the second material layer on the surface of the seed crystal. 2. A temperature gradient is applied to the heating atmosphere so that the seed crystal side is on a low temperature side, and the first material layer is melted to form a melt, and the solubility of the solute in the melt depends on the temperature. 2. The crystal growth method according to claim 1, wherein the compound crystal is grown on the seed crystal by utilizing the property, and a low-temperature side surface of the second material layer is dissolved in the melt. 3. 3. The seed crystal comprises a compound of two or three elements selected from the group III-V elements, and the first material comprises one to three types of compounds selected from the group III and V elements. The second material is composed of a simple substance or a compound of an element.
3. The crystal growth method according to claim 2, comprising a compound of two or three elements selected from the group III-V elements. 4. A temperature gradient is applied to the heating atmosphere so that the seed crystal side is at a lower temperature side under a temperature condition in which the first material is melted and the entire second material is not melted. 2. The crystal growth method according to claim 1, wherein a solid phase of a compound composed of a molten element from the first material layer and the second material layer is formed on a surface of the first material layer to grow the compound crystal. 5. The seed crystal comprises a compound of two or three elements selected from the group III to V elements, and the first material comprises one to three kinds of compounds selected from the group III and V elements. The second material is composed of a simple substance or a compound of an element.
5. The crystal growth method according to claim 4, comprising a compound of two or three elements selected from the group III-V elements. 6. A melt of the first material or a solution of the seed crystal in the first material covering all or a part of the surface of the seed crystal layer other than a portion in contact with the first material layer. The crystal growth method according to claim 1, wherein the material is coated with a material having poor wettability. 7. A coating material for the seed crystal layer and the second material.
Is made of SiO ₂ , SiN or SiON
The crystal growth method according to claim 6, wherein