JPH0764671B2 - Method for growing compound semiconductor single crystal - Google Patents

Description

The present invention relates to a method for manufacturing a compound semiconductor bulk crystal such as a GaAs crystal. Specifically, it relates to the improvement of the compound semiconductor crystal manufacturing method by the vertical Britzmann method or the vertical temperature gradient solidification method in which the raw material melt is synthesized and melted in the container, and then crystallized in the container using the seed crystal. is there.

(Prior Art and Problems to be Solved by the Invention) Many reports have already been made on the crystal production method according to the present invention (for example, SEBlum and RJ Chicotka; Growth).
of Low Strain GaP by Liquid-Encapsulation, Vertic
al−Gradient Freeze Technique, Electrochemi.Soci., 1
20 (1973) 588, WAGault, EMMonberg and JECleman
s; A Novel Application of the Vertical Gradient Fre
eze Method to the Growth of High Quality IV−V Cry
stals, J.Cryst.Growth.74 (1986) 491).

FIG. 1 shows the principle of the liquid-sealed vertical Bridgeman method according to the present invention. The right side shows a schematic view of a cross-sectional view of the crucible, and the left side shows the temperature distribution inside the crucible. An example applied to a GaAs single crystal will be described below as a typical example of a compound semiconductor crystal. In the figure, reference numeral 1 is a crystal shape defining container or crucible, and 2
Is a seed crystal, 3 is a grown GaAs crystal, 4 is a raw material melt, 5
Is a liquid sealant composed of B ₂ O ₃ . Curve 6 shows the temperature distribution in the furnace during crystal growth, and the crystal growth is in the crucible 1
Are gradually moved downward, and as a result, the crystal growth interface 7
(The temperature corresponds to the melting point T _m ) gradually moves from the upper end 8 of the seed crystal 2 to the upper part, and the crystal 3 grows. On the other hand, in the vertical temperature gradient solidification method, the temperature distribution 6 in the furnace is changed while the position of the crucible 1 is fixed, that is, the temperature distribution is kept almost constant and the whole temperature is changed from the high temperature side to the low temperature side (from the right in FIG. Move it to the left in parallel). Actually, in many cases, the above-mentioned vertical Bridgeman method and vertical temperature gradient solidification method are combined to grow a crystal, and the present invention can be applied to any case. Further, in the example of FIG. 1, the liquid sealant 5 is used to prevent dissociative evaporation of As from the surface of the high-temperature raw material melt 4, but instead of this, an As atmosphere sufficient to suppress dissociative evaporation of As is used. It is known that there is also a method of keeping it at.

The feature of the present invention resides in the above-described crystal growth method, in particular, in the production of the raw material melt 4 and the process of attaching seeds at the start of crystal growth, and the conventional method and its drawbacks will be described in detail below. FIG. 5 is a schematic diagram showing a method for producing a raw material melt which has been conventionally applied. In the figure, the seed crystal 2 is inserted into the protrusion 9 provided in the lower part of the crucible 1, then the GaAs polycrystal 10 as a raw material is filled in the main part of the crucible, and the upper part is liquid-sealed. Fill solid 11 of agent B ₂ O ₃ . In the manufacturing process of the raw material melt, the temperature is gradually raised under an appropriate temperature distribution in the furnace, the B ₂ O ₃ 11 is softened, the GaAs polycrystal 10 is melted, and the manufacturing process of the raw material melt 4 is completed. The problems of such a conventional method for producing the raw material melt 4 are (i) it is necessary to previously produce a GaAs polycrystal as a raw material by another method, the number of steps for that is increased, and the crystal production cost is high. Not only that, but (ii) such an increase in the number of steps increases the chances of mixing impurities, which leads to the deterioration of the quality of the grown crystal. (Ii) Further, a serious drawback of this method is that the composition of the melt cannot be significantly changed because the polycrystal as a raw material has a substantially stoichiometric composition. This is a major disadvantage from the viewpoint of controlling the crystal characteristics by controlling the composition of the melt, which has been actively performed in the field of semi-insulating GaAs single crystals in recent years.

In order to solve these problems, the inventors have tried various raw material melt production methods that can be easily analogized from the direct synthesis method applied in the field of the liquid sealing pulling method, but this method also has a good yield. I knew that there was a problem in growing single crystals.
FIG. 6 is a schematic view showing a raw material charging method in the above-mentioned direct synthesis vertical Bridgeman method. In the figure, 12 is GaAs
Metal Ga, which is one of the raw materials of the compound, represents metal As. In the process for producing the GaAs raw material melt by the direct synthesis method, the raw materials are filled in the crucible 1 as shown in FIG. 6, and then the crucible 1 is heated and heated in the furnace. As the temperature rises, first the metallic Ga12 melts (melting point 29 ° C), then the sealing agent B ₂
O ₃ 11 softened (400 to 600 ° C.), and as shown in FIG. 7 (a), a mixture of Ga melt 14 and solid metal As 13 was present above the seed crystal 2, and the upper portion of these was liquid and summer were B ₂ O ₃
5 seals. When the temperature is further increased, metal As1
3 melts (melting point 820 ° C) and at the same time reacts with the melted Ga14
GaAs is synthesized. FIG. 8 (a) is a schematic view showing this state, in which 15 is a synthesized GaAs crystal. From this state, the temperature is further raised, and the boundary portion 16 between the GaAs crystal 15 synthesized with the seed crystal 2 is set as the melting point of the GaAs crystal, and the furnace temperature and the temperature distribution are adjusted so that the upper portion thereof becomes a temperature higher than the melting point. As a result, a raw material GaAs melt is realized and the raw material GaAs synthesis / melting process is completed.

FIG. 9 shows the boundary portion of the seed crystal 2 after GaAs synthesis and melting as described above.
Starting crystal growth from 16, is a schematic diagram of a single crystal growth process showing the state during growth of the constant diameter portion 1b through the increased diameter portion 1c,
19 indicates a crystal growth interface and 20 indicates a GaAs melt. The figure (b) shows the enlarged view of the boundary part in the figure (a).

As a result of various investigations on the characteristics of the GaAs crystal obtained by the synthesis / melting of the raw material GaAs and the single crystal growing process as described above, the inventors have found that these crystals have a large problem in growing the single crystal with good reproducibility. There was found. Specifically, as shown in the enlarged schematic view of FIG. 9 (b), high density dislocations originating from the seed crystal 2 part, small tilt boundaries, and defects 25 such as subgrains are generated, causing crystal growth. That is, it becomes a polycrystal with the progress of. Furthermore, as a result of various consideration and examination of these causes, the following causes were found.
As shown in the enlarged view of Fig. 7 (b), Ga14 melted and touched the surface of the seed crystal 2 made of GaAs during the synthesis process to make the interface shape of the seed crystal 21 irregular. At the same time, the crystal quality of the seed crystal is significantly deteriorated.

As described above, when the direct synthesis method frequently used in the field of the liquid sealing pulling method is directly applied to the vertical Bridgeman method according to the present invention, the deterioration of the seed crystal is unavoidable and the single crystal growth with good reproducibility is achieved. Became difficult.

(Object of the Invention) The present invention has been proposed to solve these drawbacks, and an object thereof is to provide a method for growing a compound semiconductor single crystal which grows a single crystal with good reproducibility by a direct synthetic vertical Bridgeman method. That is. Before the present invention, an invention (Japanese Patent Application No. 61-215980) made for almost the same purpose as the present invention has been proposed, but the present invention is simpler and more effective than these conventional methods. It enables the growth of a single crystal.

(Means for Solving Problems) In order to achieve the above-mentioned object, the present invention is to fill a seed crystal in the lower part of a crystal shape defining container, and then to the upper part of the seed crystal, a compound to be grown. A cap layer composed of a single crystal or a polycrystal having the same composition as the crystal or a composition close to that of the crystal is filled, and an elemental raw material composed of two or more elements mixed in a required composition ratio is provided on the upper part of the cap layer. A step of filling, a step of synthesizing a desired compound polycrystal from the raw material composed of the two or more elements in the container, and a step of synthesizing the compound polycrystal thus synthesized and the compound of the cap layer. A step of melting the crystal, and then growing the melted melt and the seed crystal into a single crystal having a predetermined orientation and shape in the container, Compound A method for growing a single semiconductor single crystal is the gist of the invention.

FIG. 2 schematically shows the method of filling the raw material into the crucible, which shows the main feature of the present invention. In the figure, 1 is a crucible, and regarding the shape of the crucible 1 used in the method of the present invention,
A feature is that a diameter-increasing portion 1c is provided between the protrusion 1a having a generally cylindrical shape in the lower portion of the crucible 1 and the constant-diameter portion 1b in the upper portion. Here, in the raw material filling method according to the present invention, after the seed crystal 2 is inserted into the protruding portion 1a, it is synthesized or grown in advance on the lower portion of the increased diameter portion 1c or the fixed diameter portion 1b, or both. The main feature is to fill the cap layer 24 made of GaAs polycrystal or single crystal (which acts as a solid to suppress the contact between the seed crystal and the melt in the initial state). The cross-sectional shape of the cap layer 24 is preferably the same as the cross-sectional shape of the crucible 1, and the effect of the present invention is to arrange the cap layer 24 as closely as possible to the crucible with the cap layer 24 being filled. It is a big thing. Next, the upper portion of the cap layer 24 is filled with metal Ga12 and metal As13 which are the raw materials weighed in a required ratio, and then the encapsulant 11 made of B ₂ O ₃ or the like. The filling method / arrangement of the metal Ga 12, the metal As 13, the sealant 11 and the like is the same as the filling method by the conventional direct synthesis method, and no special limiting condition is required.

Ga after filling the raw materials by the method according to the present invention described above
The synthesis process of As polycrystal 15 and the production process of GaAs melt 20 are as follows. FIG. 3 is a schematic view showing a state after GaAs polycrystal 15 is synthesized by the method of the present invention. Since the temperature at which GaAs polycrystal is formed from Ga and As is lower than the temperature at which GaAs single crystal or polycrystal melts, the cap layer cannot be removed.
In the figure, 24 is pre-filled in FIG.
This is a cap layer made of GaAs, and the synthesized GaAs polycrystal 15 exists on the upper part of the cap layer 24.
It is a feature of the synthesis process according to the present invention that there is no newly synthesized GaAs polycrystal between the seed crystal 2 and the cap layer 24 under 24. Next, the melting process of the synthesized GaAs polycrystal 15 and the filled GaAs crystal cap layer 24 is performed by the GaAs polycrystal 15 on the top of the crucible 1 and then the GaAs crystal cap layer 24.
Melted gradually in the order of, and finally the upper part 2a of the seed crystal 2 was GaAs.
Keep the melting point of the crystal (1238 ℃) and finish.

In other words, the order of single crystal growth in the present invention is as follows: (i) melting Ga and As (elementary raw material) to synthesize GaAs polycrystal (about 850 ° C.), and (ii) trying to grow The cap layer made of a single crystal or a polycrystal having the same or similar composition as the compound crystal and the GaAs polycrystal obtained in the step (i) are melted (1238 ° C. or higher), and (iii) above (ii) The purpose is to grow the melt and the seed crystal obtained in the step (1) into a single crystal having a desired orientation and shape.

As described above, according to the method of synthesizing and growing a compound semiconductor crystal such as a GaAs crystal according to the present invention, the raw material is filled in the crucible by the method shown in FIG. 2 and the GaAs crystal is further prepared in the state shown in FIG. As shown in FIG. 7 (b), the shape irregularity of the seed crystal interface 21
Does not occur, and as a result, the defect as shown in FIG. 9 (b)
It is possible to grow a high quality single crystal without the generation of 25.

Next, examples of the present invention will be described. Needless to say, the embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the present invention.

(Example 1) An example in which the raw material charging method shown in FIG. 2 is applied will be described below. The shape and dimensions of the crucible 1 used is such that the inner diameter of the constant diameter portion 1b is approximately
80 mm, the inner diameter of the lower protrusion 1a is 4 mm, and the increased diameter portion 1c has an inclination angle of about 45 °. The material of this crucible is pyrolytic boron nitride (PBN). A seed crystal (GaAs single crystal) 2 having a diameter of about 4 mm and an orientation of <100> was inserted into the protrusion 1a of the crucible 1 described above. Next, the cap layer 24 of the GaAs crystal raw material is a disk shape with a diameter of about 80 mm and a thickness of about 15 mm that has been cut out from a polycrystalline ingot synthesized in advance using a crucible of almost the same shape and subjected to cleaning / etching treatment. And weighs about 40
It is 0g. The upper portion of the cap layer 24 of these GaAs crystal raw materials was alternately filled with metal Ga (solid) 12 1500.0 g and metal As 13 1645 g. Furthermore, a diameter of about 75 m is above the raw materials.
The raw material filling process was completed by loading solid B ₂ O ₃ 11 having a thickness of 30 mm and a thickness of 30 mm (weight of about 240 g). Next, the metallic raw material Ga12
In the process for synthesizing GaAs polycrystal 15 from Al and metal As13, the temperature was gradually increased in the furnace at a pressure of about 65 atm (Ar gas atmosphere) under the temperature distribution (the upper part of the crucible was higher than the lower part) as shown in Fig. 1. When the temperature of the filled GaAs crystal raw material 24 reaches approximately 850 ° C (estimated from the temperature measurement at the outer periphery of the crucible 1), the temperature is stopped and held for a certain period of time, and this process is completed. did. This temperature does not melt the solid GaAs crystals (single crystal and polycrystal), while it is sufficient to melt both Ga and As to form GaAs polycrystal. Next, these synthesized GaAs polycrystals 15 and filled GaAs crystal raw materials 24
The melting point of the seed crystal 2 is the melting point (1238 ° C) of the GaAs crystal at the upper end 2a of the seed crystal 2 under the temperature distribution shown in Fig. 1.
The temperature was raised until the temperature reached, and the temperature was maintained for a certain period of time to complete the melting process. Incidentally, the subsequent single crystallization process was carried out by a method substantially similar to the conventional crystal growth method by the vertical Bridgeman method.

The obtained crystal with a diameter of about 80 mm was a single crystal in the growth direction <100>, and dislocations distributed in the plane at a density of 5 × 10 ³ to 10 ⁴ g / cm ³ were observed, but the seed crystal part No high-density dislocation distributions or crystal boundaries originating from the crystal were found. On the other hand, regarding electrical characteristics, the specific resistance was 5 to 10 × 10 ⁷ Ω-cm, and stable semi-insulating property without thermal transformation was shown. Further, the weight reduction amount at the end of the single crystal growth with respect to the raw material filling is 12 g, and assuming that the entire weight reduction is the evaporation amount of As during the raw material synthesis, the initial melt composition of the crystal growth is As / ( Ga + A
s) = 0.503, and it can be inferred that the crystal grown from this melt is a semi-insulating crystal in which the residual shallow acceptor level is compensated by the deep donor level due to point defects.

(Embodiment 2) FIG. 4 is a schematic view showing a raw material charging method according to another embodiment of the present invention. The feature of this embodiment is that (i) the seed crystal 2 and the GaAs crystal raw material 24 use an integrated crystal ingot, and (ii) or one of the raw materials, metallic Ga, is initially filled with Ga to increase the packing density. For example, the material is heated and melted at a temperature equal to or higher than the melting point and filled as liquid Ga. Other filling methods and GaAs polycrystal synthesis, melting, and single crystal growth processes are the same as those described in the first embodiment.

The obtained results showed that the entire crystal was a single crystal as in the case of Example 1 and that the electrical characteristics were stable and showed a semi-insulating property.

This embodiment also has an advantage that the increased diameter portion of the crystal ingot, which cannot be usually processed into a wafer and used as the GaAs crystal raw material 24 to be filled in the upper portion of the seed crystal 2, can be effectively used.

FIG. 10 schematically shows the state in the crucible in the crystal growing state. In the figure, 2 is a seed crystal, 17 is a grown GaAs crystal, and 16 is a boundary between the seed crystal and the grown crystal. In the crystal of the conventional method, the surface of the seed crystal 2 is melted and touched by Ga melted at the time of raw material synthesis to cause shape irregularity, which causes defects to be introduced into the grown crystal. However, in the crystal according to the method of the present invention, since Ga is a capping layer and does not come into direct contact with the seed crystal 2, no shape irregularity occurs and a single crystal having no defects can be obtained.

(Effects of the Invention) As described above, the present invention provides a method of filling a crucible with a raw material, synthesizing and melting a raw material in a compound semiconductor crystal manufacturing method by a vertical Britzmann method using a seed crystal or a vertical temperature gradient solidification method. With significant improvements made to the process, etc., the seed crystal is filled in the lower part of the crystal shape defining container, and then the upper part of the seed crystal is composed of the same or close composition as the compound crystal to be grown. Synthesis and melting of raw material by filling a cap layer made of single crystal or polycrystal, and filling the upper part of the cap layer with a raw material made of two or more elements mixed in a necessary composition ratio. The deterioration of the seed crystal in the process is prevented, and this seed crystal enables the reproducible growth of a single crystal with few defects. Further, according to the present invention, since the raw material melt is produced by the direct synthesis method, the composition of the melt can be freely selected, and since no other crystal raw material synthesized by another process is used, It has many advantages in terms of crystal growth and crystal quality, such that impurities can be reduced in the liquid and further in the grown crystal.

Although the present invention has been described in detail so far with respect to GaAs crystal growth, the present invention is not applied only to GaAs crystals, and by appropriately selecting the temperature conditions in the furnace, atmospheric pressure conditions in the furnace, etc. It can also be applied to the growth of many other types of compound crystals and mixed crystals such as InP, GaP and InAs.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the vertical Bridgeman method or the vertical temperature gradient solidification method according to the present invention, FIG. 2 is a schematic diagram showing an embodiment of the present invention, and FIG. 3 is a raw material synthesis by the method of the present invention. FIG. 4 is a schematic diagram showing the latter state, FIG. 4 is a schematic diagram showing another embodiment of the present invention, FIGS. 5 and 6 are schematic diagrams showing a conventional raw material filling method, and FIG. Fig. 8 is a schematic diagram during the raw material synthesis by the method of Fig. 8, Fig. 8 is a schematic diagram showing the state after the raw material polycrystal synthesis by the conventional method, Fig. 9 is a schematic diagram during the conventional single crystal growth, and Fig. 10 is the present It is drawing explaining the effect of invention. 1 ... crucible 1a ... crucible protrusion 1b ... crucible constant diameter portion 1c ... crucible increased diameter portion 2 ... seed crystal 3 ... growing crystal 4 ... raw material melt 5 ... liquid sealant 6 ...... furnace temperature distribution curve 7 ...... crystal growth interface 8 ...... seed crystal upper portion 9 ...... for inserting a seed crystal projections 10 ...... GaAs polycrystal 11 ...... B ₂ O ₃ liquid made of Sealant 12 …… Metal Ga (raw material) 13 …… Metal As 14 …… Liquid Ga melt 15 …… Synthesized GaAs polycrystal 16 …… Interface 17 …… Growing single crystal 18 …… Constant-diameter part of grown single crystal 19 …… Crystal growth interface 20 …… Material GaAs melt 21 …… Type irregularity of seed crystal top 23 …… Defects introduced into seed crystal 24 …… Filled according to the present invention Cap layer of GaAs source 25 .. Defects in grown crystal inherited from seed crystal part

Claims (2)

[Claims] 1. A seed crystal is filled in a lower portion of a crystal shape defining container, and then a single crystal or a polycrystal having a composition similar to or close to that of a compound crystal to be grown is provided in an upper portion of the seed crystal. And a cap raw material consisting of two or more elements mixed in a necessary composition ratio on the upper part of the cap layer, and then in the container, two or more of the above two or more kinds. A step of synthesizing a desired compound polycrystal from an elemental raw material consisting of the element, then melting the synthesized compound polycrystal and the compound crystal of the cap layer, and then melting the melt. And a step of growing the seed crystal into a single crystal having a predetermined orientation and shape in the container, the method for growing a compound semiconductor single crystal. 2. A shape-defining container is composed of a protrusion having a smaller diameter than the lower portion, then a diameter-increasing portion and a constant-diameter portion having a large diameter and a substantially constant diameter. The upper portion of the seed crystal, that is, the lower portion of the increased diameter portion and / or the lower portion of the constant diameter portion, or both, is charged with a compound crystal raw material, and the upper portion of the compound crystal raw material is sequentially filled with an elemental raw material composed of two or more elements. The method for growing a compound semiconductor single crystal according to claim 1, which is characterized in that.