JPH10287500A - Heat treatment of semi-insulating gallium arsenic single crystal and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide both a method for heat-treating a semi-insulating GaAs single crystal having an increased number of wafers to be heat-treated per unit time and an apparatus therefor. SOLUTION: Semi-insulating GaAs single crystal wafers 3 are sandwiched between wafers 2 made of graphite composed of a substance having a higher thermal conductivity than that of the GaAs and housed in an ampul 1 to thereby adjacently arrange the wafers 3. As a result, the space efficiency of the wafer annealing can be enhanced. That is, the same heating efficiency just as that in the case of sandwiching thin planer heaters between the wafers 3 can be obtained by sandwiching the wafers 3 between the wafers 2, made of the graphite and having a high thermal conductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semi-insulating GaAs.
The present invention relates to a single crystal heat treatment method and apparatus.

[0002]

2. Description of the Related Art Semi-insulating GaAs single crystals are widely used as substrate materials for high-speed high-frequency devices such as FETs (field-effect transistors) and LSIs (large-scale integrated circuits) and magneto-electric conversion devices such as Hall devices. I have. A pulling method (LEC method) using a liquid sealant (B ₂ O ₃ ) as a method for producing a semi-insulating GaAs single crystal used for these devices.
Is generally known. Large diameter as an advantage of the pulling method,
It is possible to increase the length and obtain a high-purity crystal, but the disadvantages are that the electrical characteristics are not uniform due to the difference in composition in the crystal pulling axis direction and the difference in the thermal history of the crystal during crystal growth. To invite.

[0005] In a semi-insulating GaAs single crystal, a crystal defect called “EL ₂ ” is formed in which excessively incorporated boron atoms behave as an electrically deep level donor. This EL ₂ is important for maintaining semi-insulating properties. In the semi-insulating GaAs single crystal manufactured by the pulling method, the distribution of EL ₂ is non-uniform, and the distribution of electric characteristics is non-uniform. Since EL ₂ can be produced and disappeared by changing the temperature, heat treatment is performed, and the electrical characteristics are made uniform by making the EL ₂ distribution uniform.

As a heat treatment method, there are a method of heat treating a single crystal block and a method of heat treating a single crystal wafer.

A method of heat-treating a single crystal block is to insert a single crystal block and a small amount of As into a quartz ampoule, evacuate the inside of the quartz ampule, make a sealed cut, apply heat from the outside to bring the single crystal to 1000 ° C. Temperature, and after holding at that temperature for several hours to several tens of hours, cooling down at a certain gradient or holding at a temperature exceeding 1000 ° C. for several hours to several tens of hours, then lowering and raising the temperature in several steps It is generally known that the holding is repeated (ingot annealing). This ingot annealing has good space efficiency in the furnace.

On the other hand, a method of heat treating a single crystal wafer is as follows.
Although the same heat treatment as that of the single crystal block is performed (wafer annealing), the holding time can be shortened because the heat capacity is small. In addition, the temperature followability is good, and the thermal distortion at the time of temperature rise and fall is alleviated by warping and bending due to the thin shape of the wafer, and there is no fear of cracks or crystal defects in the ingot (this warping or bending is caused by the wafer. Can be removed by polishing).

[0007]

However, in the above-mentioned conventional technique, when a single crystal block is subjected to heat treatment,
The high-temperature holding time required to improve the electrical uniformity is generally 10 hours or more because it is necessary to uniformly heat the single-crystal block to the center, and the time required for heating, cooling, and repetition thereof is required. It lasts more than two full days. In addition, there is a restriction on the thermal conductivity of the crystal (smaller than metal, carbon, etc.), so that even if the rate of temperature rise and fall is increased, the temperature followability of the crystal is poor. Further, since the heat capacity is larger than that of the wafer state, the temperature followability is inferior to that of the wafer. Increasing the rate of temperature rise and fall in the state of the crystal causes cracks in the crystal and induces crystal defects such as slip dislocations in the crystal when the thermal strain induced by the temperature rise and temperature decrease is relaxed. I will.

On the other hand, when the single crystal wafer is heat-treated, the heat capacity is smaller than when the single crystal block is heat-treated, so that the high temperature holding time can be about 1/3 and the same uniformity can be obtained. The number of heat treatments is extremely smaller than the number of wafers that could be obtained from a single crystal block, resulting in poor space efficiency. Conversely, if the distance between wafers is reduced to increase the number of heat-treated wafers, there is a problem that a heat treatment time equivalent to that of a single crystal block is required.

It is an object of the present invention to solve the above-mentioned problems and to provide a method and an apparatus for heat treating a semi-insulating GaAs single crystal in which the number of heat treatments per unit time of a wafer is increased.

[0010]

According to the present invention, there is provided a method for heat-treating a semi-insulating GaAs single crystal according to the present invention, which comprises heat-treating a semi-insulating GaAs single crystal wafer. It is sandwiched between substances having higher thermal conductivity.

An apparatus for heat-treating a semi-insulating GaAs single crystal wafer according to the present invention is an apparatus for heat-treating a semi-insulating GaAs single crystal wafer, which is arranged so as to sandwich each wafer and has a higher thermal conductivity than GaAs. And an ampoule accommodating the thermally conductive wafer and the semi-insulating GaAs single crystal wafer.

According to the present invention, the space efficiency of wafer annealing can be increased by arranging the semi-insulating GaAs single crystal wafers close to each other.

However, simply bringing the wafers close to each other blocks the radiant heat. Considering the ingot shape, which is extremely close, the heat capacity becomes large, and the temperature rise and fall are restricted. Further, when the wafer is warped or bent, the wafers come into contact with each other to cause cracks or distortion.

In view of the above, according to the present invention, each wafer is sandwiched between materials having higher thermal conductivity than GaAs (the wafer does not contact the material having high thermal conductivity, but the contact is not limited). In addition, the space efficiency of wafer annealing can be improved. By sandwiching each wafer with a substance having a higher thermal conductivity than GaAs, the same heating efficiency can be obtained as if a thin surface heater is sandwiched between the wafers.

Here, the thermal conductivity of GaAs varies depending on the temperature. For example, at 1100 ° C., about 10 W / mK
It is. That is, when heat treatment is performed at 1100 ° C., Ga
A substance having a higher thermal conductivity than As has a thermal conductivity of 10 W / mK.
Substances exceeding the target. For example, graphite is 11
A thermal conductivity of about 60 W / mK at 00 ° C. is a preferable substance.

[0016]

Embodiments of the present invention will be described below in detail.

The heat treatment method for a semi-insulating GaAs single crystal according to the present invention is a method for heat-treating a wafer of a semi-insulating GaAs single crystal, wherein each wafer is sandwiched between substances having higher thermal conductivity than GaAs. By sandwiching each wafer with a substance having a higher thermal conductivity than GaAs, the wafers are arranged close to each other, so that the space efficiency of wafer annealing can be increased, and the number of heat treatments per unit time of the wafer can be increased. Can be.

[0018]

EXAMPLE A semi-insulating GaAs single crystal having a weight of 11,000 g, an outer diameter of 76 mm, and a length of about 320 mm was produced by a pulling method using 6000 g of Ga, 6500 g of As, and 1200 g of a liquid sealant (B ₂ O ₃ ). Both ends are cut and cylindrically ground to an outer diameter of 76 mm.
aAs cylinder was prepared and cut to a thickness of 0.7 mm.
00 sheets were prepared, washed and etched.

On the other hand, a graphite wafer having an outer diameter of 76 mm and a thickness of 1 mm was cleaned.

FIG. 1 is a longitudinal sectional view of an ampule used in an apparatus to which the method for heat treating a semi-insulating GaAs single crystal of the present invention is applied.

Referring to FIG. 1, a graphite wafer 2 and a GaAs wafer 3 as heat conductive wafers are alternately inserted into a cleaned and dried quartz ampoule 1 so that the As pressure in the ampoule 1 is reduced. The amount of As4 to be compensated is charged and vacuum sealing is performed. This ampoule 1 at 1100 ° C
For 7 hours, 500 ° C. for 7 hours, and 750 ° C. for 7 hours.

As a comparative example, 60 GaAs wafers manufactured according to the same specifications as those of the embodiment were arranged at intervals of 5 mm so that the entire length was the same as that of the embodiment, and heat treatment was performed under the same conditions as the embodiment.

(Comparative Example 1) Sixty GaAs wafers manufactured with the same specifications as those of the example were arranged at intervals of 5 mm, and the heat treatment was performed under the same conditions as those of the example so that the total length was the same as that of the example.

(Comparative Example 2) A GaAs cylinder having an outer diameter of φ76 mm and a length of 250 mm manufactured in the same specification as the example was inserted into a quartz ampoule as in the example, and after vacuum sealing, heat treatment was performed under the same conditions as in the example. went. Thereafter, the wafer was cut into a thickness of 0.7 mm to produce 200 wafers.

As for the GaAs wafers for evaluation, the positions in the quartz ampules of the wafers of Example 1 and Comparative Example 1 were sampled one by one from the left end, the center, and the right end. From Comparative Example 2, the GaAs cylinders in the quartz ampules were sampled. The center of the wafer was cut from the left, center and right ends. The EL ₂ concentration of each wafer was measured by an infrared absorption method as uniformity evaluation, also,
The specific resistance was measured by the Pau method. Table 1 shows each measurement result.

[0026]

[Table 1]

Table 1 shows that there is no difference between the example and the comparative example 1 and that the uniformity is improved as compared with the comparative example 2.

As described above, according to the present invention, (1) the number of heat-treated semi-insulating GaAs wafers can be increased.

(2) Semi-insulating GaAs with uniform electric characteristics
A wafer can be obtained.

[0030]

In summary, according to the present invention, the following excellent effects are exhibited.

By sandwiching each wafer with a substance having higher thermal conductivity than GaAs, it is possible to provide a method and apparatus for heat treating a semi-insulating GaAs single crystal in which the number of heat treatments per unit time of the wafer is increased.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an ampule used in an apparatus to which a heat treatment method for a semi-insulating GaAs single crystal of the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ampoule 2 Graphite wafer 3 Semi-insulating GaAs single crystal wafer 4 As

Claims (2)

[Claims] 1. A method of heat-treating a semi-insulating GaAs single crystal wafer, wherein each wafer is sandwiched between substances having higher thermal conductivity than GaAs. 2. An apparatus for heat-treating a semi-insulating GaAs single crystal wafer, comprising:
a thermally conductive wafer made of a substance having a higher thermal conductivity than aAs, and an ampoule accommodating the thermally conductive wafer and the semi-insulating GaAs single crystal wafer. Crystal heat treatment equipment.