JP2004026584A - METHOD OF MANUFACTURING GaAs SINGLE CRYSTAL AND GaAs SINGLE CRYSTAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a GaAs single crystal by which the heat treating time is reduced and the productivity is improved, and a method of manufacturing a GaAs substrate. <P>SOLUTION: The GaAs single crystal obtained by growing a GaAs seed crystal by a vertical boat method is heat treated at ≥800°C to ≤1130°C for ≥10 min to <1,200 min. The GaAs substrate is obtained by slicing the GaAs single crystal. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a GaAs single crystal, a method for manufacturing a GaAs substrate, and a GaAs single crystal.
[0002]
[Prior art]
GaAs has advantages such as high electron mobility and the possibility of forming a heterojunction maintaining crystallinity with other mixed crystals. Therefore, GaAs is used for various semiconductor devices, and the demand for GaAs is increasing. Is going on. Since GaAs is a compound semiconductor and does not exist in nature, it is manufactured by preparing a seed crystal of GaAs, growing the seed crystal, and then performing a heat treatment. As a method of growing a GaAs seed crystal, there is a LEC method (Liquid Encapsulated Czochralski method).
[0003]
In the LEC method, a GaAs seed crystal is grown by rotating and pulling the GaAs seed crystal while rotating the GaAs seed crystal in a state where arsenic does not dissociate and evaporate from the GaAs source melt. Is what you get. This method has an advantage that the crystal can be highly purified, and a large-diameter crystal can be easily grown by increasing the size of the crucible in which the raw material melt is placed.
[0004]
Conventionally, a GaAs single crystal has been manufactured by growing a crystal by such an LEC method and then performing a heat treatment to make the specific resistance in the crystal uniform.
[0005]
[Problems to be solved by the invention]
However, the heat treatment in the above manufacturing process generally needs to be performed for several tens of hours, and has a problem that the heat treatment time is long and the productivity is low.
[0006]
The present invention has been made to solve the above problems, and has as its object to provide a method of manufacturing a GaAs single crystal and a method of manufacturing a GaAs substrate, which have a short heat treatment time and high productivity.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a GaAs single crystal according to the present invention comprises the steps of: growing a GaAs single crystal by growing a crystal on a GaAs seed crystal by a vertical boat method; Performing a heat treatment at a temperature below for at least 10 minutes and less than 1200 minutes.
[0008]
The reason why the heat treatment time is set to 10 minutes or more and less than 1200 minutes is that when heat treatment is performed on a GaAs single crystal at a predetermined temperature, the uniformity of the specific resistance required as a semiconductor material can be realized in the heat treatment time of 10 minutes or more. Further, when the heat treatment time is 1200 minutes or more, the uniformity of the specific resistance in the crystal becomes constant, so that there is no need to perform any further heat treatment.
[0009]
According to the manufacturing method of the present invention, a GaAs single crystal can be obtained in a short heat treatment time, so that a GaAs single crystal can be manufactured with high productivity. It is considered that the short-time heat treatment is sufficient because a GaAs single crystal having a low dislocation density can be obtained by growing a crystal by the vertical boat method.
[0010]
In another method for producing a GaAs single crystal of the present invention, a GaAs single crystal having a dislocation density of 1 × 10 ² cm ⁻² or more and 1 × 10 ⁴ cm ⁻² or less is formed at a temperature of 800 ° C. or more and 1130 ° C. or less for 10 minutes. The heat treatment is performed for less than 1200 minutes.
[0011]
The reason why the heat treatment time is set to 10 minutes or more and less than 1200 minutes is that when heat treatment is performed on a GaAs single crystal at a predetermined temperature, the uniformity of the specific resistance required as a semiconductor material can be realized in the heat treatment time of 10 minutes or more. Further, when the heat treatment time is 1200 minutes or more, the uniformity of the specific resistance in the crystal becomes constant, so that there is no need to perform any further heat treatment.
[0012]
According to the manufacturing method of the present invention, a GaAs single crystal can be obtained in a short heat treatment time, so that a GaAs single crystal can be manufactured with high productivity. It is considered that short-time heat treatment is sufficient because the dislocation density of the GaAs single crystal is low.
[0013]
The GaAs single crystal of the present invention is a GaAs single crystal manufactured by any one of the GaAs single crystal manufacturing methods described above, has a specific resistance of 1 × 10 ⁷ Ωcm or more, and has a standard of a specific resistance value in each part of the GaAs single crystal. The variation of the specific resistance obtained from (standard deviation) × 100 / (average value) based on the deviation and the average value is not more than 8%. The GaAs single crystal of the present invention has semi-insulating properties and a substantially uniform specific resistance in the crystal, and thus is useful as a semiconductor material.
[0014]
A method of manufacturing a GaAs substrate according to the present invention includes a step of obtaining an ingot of a GaAs single crystal by any one of the above-described methods of manufacturing a GaAs single crystal, and a step of obtaining a GaAs substrate by slicing the ingot. Since the GaAs single crystal manufacturing method can manufacture a GaAs single crystal ingot with high productivity, a high-quality GaAs substrate having substantially uniform specific resistance can be provided at low cost.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a GaAs single crystal manufacturing method and a GaAs substrate manufacturing method according to the present invention will be described in detail with reference to the accompanying drawings. The same elements will be denoted by the same reference symbols, without redundant description.
[0016]
The method for manufacturing a GaAs single crystal of the present embodiment includes the steps of (1) obtaining a GaAs single crystal by growing a crystal on a GaAs seed crystal by a vertical boat method, and then (2) subjecting the GaAs single crystal to 800 ° C. or higher and 1130 ° C. The GaAs single crystal is manufactured by performing a heat treatment at the following temperature for 10 minutes or more and less than 1200 minutes.
[0017]
First, a step of growing a crystal on a seed crystal by the vertical boat method will be described with reference to FIG. The vertical boat method (Vertical Boat method) is a method in which a GaAs seed crystal 10 is attached to the tip of a vertically placed crucible 6 made of pBN or the like, a GaAs raw material is put into the crucible 6, and the GaAs raw material is melted. This is a method of obtaining a GaAs single crystal 12 by solidifying a GaAs raw material melt 14 in order from the crystal 10 side. The vertical boat method includes a vertical Bridgman method and a vertical gradient freeze method.
[0018]
In the vertical Bridgman method, the crucible 6 and the heater 4 surrounding it are moved relatively vertically. The heater 4 has a temperature gradient and maintains a constant temperature distribution such that the temperature gradually decreases vertically downward. After the seed crystal 10 is attached to the lower end of the inside of the crucible 6, a GaAs raw material is put into the crucible 6, and the GaAs raw material is melted. The crucible 6 is sealed with a liquid sealant 16 made of B ₂ O ₃ or the like in order to suppress the dissociation of arsenic from the melted GaAs raw material melt 14. By gradually moving the crucible 6 vertically downward with respect to the heater 4, the temperature of the lower portion of the GaAs raw material melt 14 becomes lower than the freezing point, so that the GaAs raw material melt 14 maintains crystallinity with respect to the seed crystal 10. While gradually solidifying. Thereby, the GaAs single crystal 12 can be obtained.
[0019]
On the other hand, in the vertical gradient freeze method, the relative positional relationship between the heater 4 and the crucible 6 is maintained. After the seed crystal 10 is attached to the lower end of the crucible 6, the GaAs material is put into the crucible 6, melted, and the crucible 6 is sealed with the liquid sealant 16, as in the case of the vertical Bridgman method. . While maintaining the relative positional relationship between the heater 4 and the crucible 6, the temperature of the heater 4 is lowered under programmed optimal conditions, whereby the GaAs raw material melt 14 is gradually solidified. Thereby, the GaAs single crystal 12 can be obtained. Hereinafter, the vertical Bridgman method and the vertical gradient freeze method are collectively referred to as a VB method.
[0020]
According to the VB method, the symmetry of the temperature distribution during the crystal growth can be maintained, and the crystal can be grown under a very gentle temperature gradient. Therefore, the dislocation density is 1 × 10 ² cm. A GaAs single crystal 12 of not less than ^{−2 and not} more than 1 × 10 ⁴ cm ⁻² can be obtained.
[0021]
Next, a step of performing a heat treatment on the GaAs single crystal 14 in a heating furnace at a temperature of 800 ° C. or more and 1130 ° C. or less for 10 minutes or more and less than 1200 minutes will be described. First, the reason for performing the heat treatment at a temperature of 800 ° C. or more and 1130 ° C. or less will be described. As a characteristic of the semiconductor material, it is desired that the semiconductor material has a semi-insulating property and a specific resistance in the semiconductor material is uniform. The GaAs single crystal 14 has a semi-insulating property, but has a disadvantage that the resistivity distribution is non-uniform.
[0022]
Therefore, by performing a heat treatment on the GaAs single crystal 14 at a temperature of 800 ° C. or more and 1130 ° C. or less, a semi-insulating property having a specific resistance of 1 × 10 ⁷ Ωcm or more is realized and the specific resistance is made uniform. One of the factors governing the specific resistance is a defect called EL2, which is electrically active and determines the electrical characteristics of the crystal. In order to realize the semi-insulating property with a specific resistance of 1 × 10 ⁷ Ωcm or more, the concentration of EL2 needs to be 1 × 10 ¹⁶ cm ⁻³ or more. Further, in order to make the specific resistance uniform, it is necessary that the concentration distribution of EL2 is uniform.
[0023]
FIG. 2 shows the dependence of the EL2 concentration on the heat treatment temperature. The vertical axis of the graph is the EL2 concentration, and the horizontal axis is the heat treatment temperature. This graph shows that the concentration of EL2 is 1 × 10 ¹⁶ cm ⁻³ or more when the heat treatment temperature is 750 ° C. or more and 1130 ° C. or less. When heat treatment is performed at a temperature higher than 1130 ° C., EL2 is decomposed and the EL2 concentration does not become 1 × 10 ¹⁶ cm ⁻³ or more. Therefore, it is possible to realize semi-insulating properties with a specific resistance of 1 × 10 ⁷ Ωcm or more. Can not. Here, if the heat treatment is performed at a temperature lower than 800 ° C., the EL2 concentration distribution in the crystal is not uniform, so that the specific resistance cannot be made uniform. Therefore, in order to realize the semi-insulating property in which the specific resistance is 1 × 10 ⁷ Ωcm or more and to make the specific resistance uniform, it is preferable to perform the heat treatment at a temperature of 800 ° C. or more and 1130 ° C. or less. .
[0024]
Next, the reason why the heat treatment time is from 10 minutes to 1200 minutes will be described in Examples.
[0025]
(Example)
The present inventors have proposed a GaAs single crystal (hereinafter, referred to as “VB crystal”) grown by the VB method and a GaAs single crystal (hereinafter, referred to as “LEC crystal”) grown by the conventionally used LEC method. For ()), the heat treatment time required to obtain a crystal having desired characteristics was compared by the following experiment.
[0026]
FIG. 3 shows a state at the time of heat treatment in the example. First, an LEC crystal ingot and a VB crystal ingot each having a diameter of 3 inches and a carbon content of 1.0 to 1.3 × 10 ¹⁵ cm were prepared using the VB method and the LEC method. From these crystal ingots, a VB crystal block 20 and a LEC crystal block 22 having a diameter of 3 inches and a thickness of 20 mm were cut out. After washing these crystal blocks, one VB crystal block 20 and one LEC crystal block 22 were sealed in the same quartz ampule 26. At this time, in order to heat-treat the VB crystal block 20 and the LEC crystal block 22 under the same conditions, as shown in FIG. 3, the VB crystal block 20 and the LEC crystal block 22 were arranged close to each other. In addition, in order to prevent arsenic from dissociating from the crystal block during the heat treatment, an appropriate amount of metal arsenic 24 was sealed in the quartz ampule 26 together with the crystal block. Several similar quartz ampules 26 were prepared.
[0027]
The quartz ampule 26 was heated at 925 ° C. by the heater 28, and the heat treatment time was different for each quartz ampule 26.
[0028]
After the heat treatment, a thin disk having a diameter of about 3 inches and a thickness of about 700 μm was cut out from each crystal block, and one side was polished. Except for 5 mm at both ends of the thin disk, on a line passing through the center of the thin disk and parallel to the orientation flat, the specific resistance at each part was measured by the three-terminal guard method at intervals of 100 μm. From the average and standard deviation of the measured resistivity,
(Standard deviation) x 100 / (average value) [%]
The variation of the specific resistance was obtained by the following. Further, a chip was cut out from the thin disk, an electrode was formed on the polished surface, and the specific resistance was measured by a van der Pauw method.
[0029]
4 and 5 show the results of the example. FIG. 4 shows the dependence of the specific resistance on the heat treatment time. The vertical axis of the graph is the specific resistance, and the horizontal axis is the heat treatment time. It can be seen that the semi-insulating property of 1 × 10 ⁷ Ωcm or more is maintained before the heat treatment and after the heat treatment for each heat treatment time. Further, the value of the specific resistance fluctuates until after 1200 minutes in the LEC crystal, whereas it reaches a steady value after 10 minutes in the VB crystal.
[0030]
FIG. 5 shows the dependence of the variation of the specific resistance on the heat treatment time. The vertical axis of the graph is the variation of the specific resistance, and the horizontal axis is the heat treatment time. Unless the LEC crystal is subjected to the heat treatment for 1200 minutes or more, the variation of the specific resistance does not become 8% or less, while the variation of the specific resistance of the VB crystal becomes 8% or less after the heat treatment time of 10 minutes. In the case of the VB crystal, when the heat treatment time is 1200 minutes or more, the variation in the specific resistance becomes a constant value. Therefore, a heat treatment time of less than 1200 minutes is sufficient. Therefore, in the case of a VB crystal, it is preferable to perform heat treatment for 10 minutes or more and less than 1200 minutes.
[0031]
In the case of a VB crystal, the value of the specific resistance is stabilized in a short heat treatment time and the specific resistance can be made uniform because the VB crystal has a lower dislocation density than the LEC crystal. it is conceivable that. Since EL2 is fixed to the dislocation, the concentration of EL2 increases around the dislocation. Therefore, when the dislocation density is low, the localization of EL2 around the dislocation is weakened, and it is considered that the variation in specific resistance is small. Therefore, it is considered that the heat treatment required for uniformizing the specific resistance is sufficient in a short time.
[0032]
The GaAs single crystal manufactured by the GaAs single crystal manufacturing method of the present embodiment has a carbon concentration of 1 × 10 ¹⁵ cm ⁻³ or more, a specific resistance of 1 × 10 ⁷ Ωcm or more, and a variation in specific resistance. 8% or less. Carbon is inevitably contained in the GaAs single crystal manufacturing process. Further, a GaAs substrate can be obtained by slicing the GaAs single crystal ingot. Since the GaAs single crystal ingot can be manufactured with high productivity by the GaAs single crystal manufacturing method, a GaAs substrate can be provided at low cost.
[0033]
As described above, the present invention has been specifically described based on the embodiments. However, the present invention is not limited to the above embodiments. For example, GaAs may be grown by a GaAs crystal growth method other than the VB method, which can obtain a GaAs single crystal 12 having a dislocation density of 1 × 10 ⁴ cm ⁻² or less.
[0034]
【The invention's effect】
As described above, according to the GaAs single crystal manufacturing method and the GaAs substrate manufacturing method of the present invention, the heat treatment time required to obtain a GaAs single crystal can be shortened, so that productivity can be improved. In addition, since a GaAs single crystal ingot can be manufactured with high productivity, a GaAs substrate can be provided at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus for growing a seed crystal by a VB method.
FIG. 2 is a diagram showing the heat treatment temperature dependence of the concentration of EL2.
FIG. 3 is a diagram showing a state at the time of heat treatment in an example.
FIG. 4 is a diagram showing the dependence of the specific resistance of a GaAs single crystal on the heat treatment time.
FIG. 5 is a diagram showing the heat treatment time dependency of the variation in the specific resistance of a GaAs single crystal.
[Explanation of symbols]
4, 28: heater, 6: crucible, 10: GaAs seed crystal, 12: GaAs single crystal, 14: GaAs raw material melt.

Claims (4)

Obtaining a GaAs single crystal by growing a crystal on a GaAs seed crystal by a vertical boat method;
Performing a heat treatment on the GaAs single crystal at a temperature of 800 ° C. or more and 1130 ° C. or less for 10 minutes or more and less than 1200 minutes;
A method for producing a GaAs single crystal, comprising: A GaAs single crystal having a dislocation density of 1 × 10 ² cm ⁻² or more and 1 × 10 ⁴ cm ⁻² or less,
A method for producing a GaAs single crystal, comprising performing heat treatment at a temperature of 800 ° C. or more and 1130 ° C. or less for 10 minutes or more and less than 1200 minutes. A GaAs single crystal produced by the GaAs single crystal production method according to claim 1 or 2,
The specific resistance is 1 × 10 ⁷ Ωcm or more;
GaAs wherein the variation of the specific resistance obtained from (standard deviation) × 100 / (average value) based on the standard deviation and the average value of the specific resistance values at a plurality of locations of the GaAs single crystal is 8% or less. Single crystal. Obtaining a GaAs single crystal ingot by the GaAs single crystal manufacturing method according to claim 1 or 2;
Obtaining a GaAs substrate by slicing the ingot;
A method of manufacturing a GaAs substrate, comprising:

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