JPH1121193A - Production of compound semiconductor single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a compd. semiconductor single crystal capable of yielding a high-quality single crystal without lowering the growth rate of the crystal. SOLUTION: This process consists in growing the single crystal of the compd. semiconductor by enclosing a crucible 1 contg. at least a compd. semiconductor raw material (GaAs polycrystal) into a hermetic vessel 4, then installing this hermetic vessel into a heating furnace 5 of a vertical type and heating and melting the raw material by a heat source (heater), then slowly cooling and solidifying the raw material melt under a prescribed temp. gradient. In such a case, the temp. difference between the max. temp. of the raw material melt and the m. p. of the compd. semiconductor is kept at <=10 to >=4 deg.C, the temp. gradient near the solid-liquid boundary between the single crystal and the raw material melt at <=4 to >=1 deg.C and the crystal growth rate at >=3 to <=50 m/h.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a compound semiconductor single crystal, and more particularly to a vertical gradient freezing (VGF) for growing a single crystal in a vertical direction by cooling a raw material melt of a compound semiconductor such as GaAs. The present invention relates to a technique that is useful when applied to a method or a vertical Bridgman (VB) method.

[0002]

2. Description of the Related Art For example, a GaAs-FET (Field Effect)
A substrate formed of a semi-insulating GaAs single crystal is used for manufacturing a GaAs-based compound semiconductor device such as a transistor or a GaAs-IC.

Conventionally, such a semi-insulating GaAs crystal has been industrially manufactured by a horizontal Bridgman (HB) method or a liquid-sealed Czochralski (LEC) method.

[0004] The LEC method has a remarkable effect on the purification of crystals, has the advantage that a semi-insulating GaAs single crystal can be obtained stably, and has the advantage of obtaining a large-diameter circular wafer. There is a merit that can be done.

[0005] However, the LEC method has a disadvantage that the temperature gradient in the crystal growth direction during crystal growth is large, so that the density of dislocations which causes the deterioration of the electrical characteristics when an FET or IC is manufactured is high. is there.

[0006] On the other hand, the HB method has an advantage that a crystal having a low dislocation density can be obtained due to a small temperature gradient during crystal growth, but the HB method has a large diameter in order to solidify a raw material melt in a crucible (boat). However, there is a disadvantage that only a wafer having a shape depending on the crucible shape (kamaboko shape) can be obtained.

Therefore, a vertical gradient freezing (VGF) method or a vertical Bridgman (VB) method has been developed as a crystal production method which compensates for the disadvantages of the HB method and the LEC method and makes use of the respective advantages. According to these manufacturing methods, a circular wafer can be obtained by using a bottomed cylindrical crucible, and the temperature gradient in the crystal growth direction is small, so that the dislocation density can be easily reduced.

Further, if a liquid sealant (B ₂ O ₃ ) is used, the incorporation of Si from a quartz ampule can be prevented, and a single crystal of an undoped semi-insulating compound semiconductor such as GaAs can be grown. It is possible.

[0009]

However, since the VGF method and the VB method can grow crystals with a smaller temperature gradient than the LEC method, as described above, the crystal defect density is low and the quality is high. On the other hand, there is an advantage that the substrate can be obtained, but on the other hand, the growth rate of the crystal is lower than that of the LEC method, and the growth time is longer.

When the crystal growth rate is increased by the VGF method or the VB method in order to reduce the growth time, the amount of latent heat of solidification per unit time increases, so that the solid side easily becomes a concave solid-liquid interface due to the influence. The defect density around the crystal increases,
There is a disadvantage that polycrystals are easily generated therefrom.

The crystal growth rate can be increased by increasing the temperature gradient. However, in that case, the crystal defect density increases, and the temperature fluctuation due to the convection of the melt accompanying the increase in the temperature gradient increases. For this reason, there is an inconvenience that the crystal is easily polycrystallized.

For this reason, in the conventional VGF method and VB method,
A method of decreasing the growth rate without increasing the temperature gradient is generally adopted, and there is a problem that the productivity of crystals per furnace is lower than that of the LEC method.

The present invention provides a method of manufacturing a compound semiconductor single crystal which can solve the above-mentioned disadvantages of the VGF method and the VB method and can obtain a high-quality single crystal without slowing down the crystal growth rate. The purpose is to do.

[0014]

In order to achieve the above-mentioned object, a method for producing a compound semiconductor single crystal according to the present invention is characterized in that a crucible containing at least a compound semiconductor material is sealed in an airtight container. In a method of growing a compound semiconductor single crystal by leaving the container in a vertical heating furnace, heating and melting the raw material by a heat source, and gradually cooling and solidifying the raw material melt under a predetermined temperature gradient, The temperature difference between the maximum temperature of the raw material melt and the melting point of the compound semiconductor is 10 ° C or less, 4 ° C or more, and the temperature gradient near the solid-liquid interface between the single crystal and the raw material melt is 4 ° C / cm or less, 1 ° C / cm or more. The crystal growth rate is set to 3 mm / h or more and 50 mm / h or less.

In the following, the present inventors outline the contents of the study and the progress of the research leading up to the present invention.

As described above, the advantages and disadvantages of the VGF method and the VB method are all caused by growing a crystal with a small temperature gradient. Since the latent heat of solidification generated when the melt solidifies is proportional to the crystal growth rate, it has been a general method to reduce the crystal growth rate with a small temperature gradient.

However, since the latent heat of solidification indicates the energy difference due to the phase transition between the liquid and the solid under the thermal equilibrium state at the melting point, the state of the system is considered to be different from the actual crystal growth. .

Therefore, the inventors have considered that even if the latent heat of solidification obtained by a general method of measuring latent heat of solidification is used as a guide, the latent heat of solidification cannot be directly applied to crystal growth.

In recent years, it has been reported that, in the growth of a Si single crystal, the melt density near the melting point changes more than the temperature-dependent change that has been considered so far. On the other hand, in II-IV group compounds such as CdTe and ZnSe, there is a report that a temperature difference between the temperature of the melt and the melting point affects the structure of the melt.

Although the details of these theoretical factors have not been elucidated yet, it can be sufficiently estimated that such a change in the melt structure also affects the conventional latent heat of solidification. The present inventors focused on the melt temperature during crystal growth and tried the following experiment.

That is, in growing a GaAs single crystal having a diameter of 3 inches and a length of 150 mm by the VGF method, the temperature gradient in the vicinity of the solid-liquid interface was set at 4 ° C./cm. If high, the other is 10 ° C
The difference in crystal quality related to the growth rate of the crystal when the height was increased was examined.

As a result, when the growth rate of the crystal is 3 mm / h or more, when the maximum temperature of the melt is higher than the melting point by about 30 ° C., the dislocation density at the crystal periphery increases from the middle of the grown crystal. Then, polycrystals were generated. On the other hand, if the temperature difference is 10
At about 4 ° C., even at 4 mm / h, the entire crystal region was a single crystal, and no increase in dislocation density was observed.

In the calculation based on the latent heat of solidification, when the crystal growth rate is about 3 mm / h, a temperature gradient of 5 ° C./cm or more is required to sufficiently dissipate the generated latent heat of solidification. However, according to the results of this experiment, it was found that even at 4 ° C./cm, latent heat of solidification could be sufficiently dissipated.

As described above, in this experiment, in growing a GaAs single crystal, the temperature gradient near the solid-liquid interface was 4 ° C./cm.
The temperature difference between the maximum temperature and the melting point of the melt was set to about 10 ° C., and the growth rate was set to 3 mm / h. However, according to the gist of the present invention, a single crystal of a compound semiconductor other than the above was formed even under other conditions. What can be grown is well speculative.

The present invention has been made by finding a condition under which a compound semiconductor single crystal can be grown without reducing the crystal growth rate even with a small temperature gradient, which has been impossible by a calculation based on general latent heat of solidification. Therefore, high productivity can be exhibited even in the VGF method or the like.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a schematic diagram showing an outline of a single crystal growth furnace by the VGF method for realizing the method of manufacturing a compound semiconductor single crystal according to the present invention.

In the method of manufacturing a compound semiconductor single crystal according to the present invention, as shown in FIG. 1, a seed crystal mounting portion (shown in FIG. 1) provided at the bottom center of a pBN crucible 1 having a diameter of 3 inches and a thickness of 1 mm, for example. A seed crystal (in this embodiment, GaAs)
Then, about 4.5 kg of GaAs polycrystal 2 as a compound semiconductor raw material and about 40 g of B ₂ O ₃ (water content: 90 ppm) as a sealant 3 are put into the crucible 1.

Subsequently, 3 g of As is put as a vapor pressure control element in a vapor pressure control section (reservoir) 4b of a quartz ampoule 4a as an airtight container 4, and the crucible 1 is placed in a susceptor (shown in the drawing) in the quartz ampule 4a. (Not shown)
The inside of the quartz ampule 4a is evacuated to vacuum and sealed with a cap.

The vacuum-sealed hermetic container 4 is placed in a vertical heating furnace 5 having, for example, a 13-stage heater as a heat source.

Then, the upper end of the seed crystal and the GaAs polycrystal (raw material) 2 are heated from 1238 ° C. to 1248 by the heater for heating the crystal growing portion and the heater for heating the seed crystal portion in the heating furnace 5.
The crucible 1 is heated to a temperature of ° C. to melt the raw material 2 and the sealing agent 3.

Since the melting point of GaAs is 1238 ° C., the temperature difference between the maximum temperature (1248 ° C.) of the raw material melt made of the GaAs polycrystal 2 and the melting point of GaAs is 10 ° C.
C. or less.

Further, in the heating furnace 5, the vapor pressure control section 4b is heated to 615 ° C. by a heater for heating the vapor pressure control section.

Next, the set temperature of the heating furnace 5 is continuously lowered so that the crystal growth rate is 3 mm / h and the temperature gradient near the solid-liquid interface is 4 ° C./cm, and crystal growth is started. During that time, the output of the heater is controlled so that the temperature of the vapor pressure control unit 4b becomes constant.

As a result of operating the single crystal growth furnace by the VGF method as in the above embodiment, all of the raw material melt was solidified at about 70 hours after the start of crystal growth.

Thereafter, the entire heating furnace 5 is cooled at a temperature decreasing rate of 100 ° C./hour, and when the temperature is cooled to near room temperature, the airtight container 4 is taken out of the heating furnace 5 and the airtight container 4 is broken to take out a crystal.

The crystal 6 obtained by the above method is a GaAs single crystal having a diameter of about 3 inches and a total length of about 150 mm. When its crystallinity was examined, no twin or polycrystal was generated.

When the dislocation density was examined by cutting this single crystal ingot, the dislocation density was 2000 cm -2 or less in any region of the crystal.

Then, GaAs is formed under the same conditions as in the above embodiment.
When single crystal growth of s was performed ten times, eight times became a single crystal, and the dislocation density was 2000 cm -2 or less.

As described above, according to this embodiment, it is possible to grow a single crystal without slowing down the crystal growth rate even with a relatively small temperature gradient, and to improve the productivity of the GaAs single crystal. Can contribute.

In the above embodiment, the case where the manufacturing method according to the present invention is applied to growing GaAs as a compound semiconductor has been described. However, the present invention is not limited to this.
Since the method according to the present invention is presumed to be effective also for single crystal growth of other compound semiconductors, GaAs
The present invention is also applicable to a case where a compound semiconductor having a zinc blende structure such as InP or GaP other than the above is manufactured by the VGF method or the like.

[0043]

According to the present invention, a crucible containing at least a compound semiconductor material is sealed in an airtight container, and then the airtight container is placed in a vertical heating furnace, and the material is heated and melted by a heat source. Then, in a method of growing a compound semiconductor single crystal by gradually cooling and solidifying the raw material melt under a predetermined temperature gradient, a temperature difference between the maximum temperature of the raw material melt and the melting point of the compound semiconductor is set to 10 ° C. In the following, the temperature gradient in the vicinity of the solid-liquid interface between the single crystal and the raw material melt is 4 ° C./cm
By setting the crystal growth rate to 1 ° C./cm or more and the crystal growth rate to 3 mm / h or more and 50 mm / h or less, it becomes possible to grow a compound semiconductor single crystal without slowing down the crystal growth rate even with a small temperature gradient. The method also has an excellent effect that high productivity can be exhibited.

[Brief description of the drawings]

FIG. 1 shows a method for manufacturing GaAs by VGF method according to the present invention.
It is a schematic diagram of a crystal growth furnace used when applying to manufacture of an s single crystal.

[Explanation of symbols]

1 crucible 2 compound semiconductor material (GaAs polycrystal) 3 sealant (B ₂ O ₃₎ 4 airtight container 5 heating furnace (heater)

Claims (2)

[Claims] 1. A crucible containing at least a compound semiconductor raw material is sealed in an airtight container, and the airtight container is placed in a vertical heating furnace, and the raw material is heated and melted by a heat source. In a method of growing a compound semiconductor single crystal by gradually cooling and solidifying under a predetermined temperature gradient, a temperature difference between the maximum temperature of the raw material melt and the melting point of the compound semiconductor is 10 ° C. or less, 4 ° C. or more, The temperature gradient near the solid-liquid interface between the single crystal and the raw material melt should be 4 ° C / cm or less, 1 ° C / c
m or more, the crystal growth rate is 3 mm / h or more, 50 mm / h
A method for producing a compound semiconductor single crystal, characterized by the following. 2. The method according to claim 1, wherein the compound semiconductor is GaAs or In.
The method for producing a compound semiconductor single crystal according to claim 1, wherein the compound semiconductor is P or GaP.