JPH0551296A - Method for producing compound semiconductor single crystal - Google Patents

Abstract

(57) [Summary] (Modified) [Constitution] In the method for growing a compound semiconductor single crystal by the LEC method, B ₂ O ₃ having a water content of 100 ppmw or less is used, and the atmosphere in the furnace after melting the compound semiconductor polycrystal is used. After the CO concentration in the gas is controlled to a constant concentration and left for a predetermined time or longer, the single crystal is grown while the CO concentration in the furnace atmosphere gas is continuously controlled to the same concentration. [Effect] The carbon concentration in the single crystal can be uniformly grown to an arbitrary value up to the tail only by the CO concentration in the furnace atmosphere gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a compound semiconductor single crystal by the LEC method.

[0002]

2. Description of the Related Art Carbon in a GaAs single crystal acts as a shallow acceptor and greatly affects the electrical characteristics of the crystal and its characteristics when a device is manufactured. For this reason, in particular, as a crystal for an IC substrate, a single crystal excellent in uniformity of carbon concentration is desired.

In the LEC method, which is industrially used as a method for producing a compound semiconductor single crystal, the CO concentration in the furnace gas is controlled in order to control the carbon concentration in the raw material melt, and thus the carbon concentration in the crystal. The method is known to be effective. Conventional methods for controlling the carbon concentration of a compound semiconductor single crystal by controlling the CO concentration in a gas and the like include JP-A-62-30700, JP-A-1-242488, JP-A-1-239089 and JP-A-1-313398. Has been reported. The method of (1) aims to reduce the carbon concentration of the crystal by making the CO or CO ₂ concentration below a certain level, and does not consider the uniformity within the crystal. The method of is a method of controlling the carbon concentration by keeping the CO concentration constant, but as described later,
Also in this case, crystals with good uniformity cannot be obtained. The method is that the carbon concentration in the crystal is 2 × 10 ¹⁵ cm ^{−3 to} 20 × 10 ¹⁵ cm ⁻³ in the head and 1/3 or more of the head concentration in the tail by controlling the carbon concentration. The uniformity is not good. Although these conventional methods can control the carbon concentration to some extent, they cannot provide sufficiently satisfactory crystals having excellent uniformity for IC substrates.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks, and an object thereof is to provide a technique for producing a compound semiconductor single crystal having a predetermined carbon concentration and excellent uniformity. ..

[0005]

[Means and Actions for Solving Problems] First, the present inventors investigated how the carbon concentration changes in a crystal when a GaAs single crystal is grown under the condition that the CO concentration is constant.

In the method for producing a compound semiconductor single crystal by the LEC method, a pressure control valve is provided in the middle of a gas introduction pipe connected to a high-pressure pulling furnace, and a valve is provided in the middle of the exhaust pipe. A CO gas detector was attached to the pulling furnace, and the crystal was pulled up while controlling the CO concentration in the pulling furnace to be constant within the range of 350 ppm ± 10 ppm based on the signal from the detector. Liquid sealant B ₂ O ₃ has a water concentration of 200 ppmw and 300 pp
The mw one was used.

As a result, the carbon concentration in the GaAs single crystal became as shown in FIG. As shown in FIG. 1, in all cases, the crystal tail was high and the uniformity was poor.

The present inventors have considered that the cause of the inconsistent carbon concentration despite the constant CO concentration is the change in the water concentration of B ₂ O ₃ .

In the LEC method, it has been previously known that the water concentration in the liquid sealant B ₂ O ₃ affects the carbon concentration of the crystal, and the B ₂ O ₃ water concentration at the time of charging and the carbon concentration of the crystal. For the relationship between ATHunter (Apply Phys Let.
44 (1), 1984). Generally, when B ₂ O ₃ having a low water concentration is used, the carbon concentration becomes high. Therefore, conventionally, B ₂ O ₃ having a water concentration of 100 ppmw or more has been used.

However, the change in the B ₂ O ₃ water concentration during crystal growth has not been investigated, and the authors investigated the B ₂ O ₃ water concentration after the growth, and as a result, as shown in FIG. It was found that the water content was much lower than the water content at the time of charging, and we thought that the carbon content would be higher on the tail side because of this.

As can be seen from FIG. 2, the B ₂ O ₃ water concentration is stable at about 100 ppmw or less. Therefore, as a means for improving the uniformity of the carbon concentration, B ₂ O having a low water concentration of 100 ppmw or less from the beginning. I decided to use ₃ . As a result, the water concentration of B ₂ O ₃ does not change during crystal growth,
Therefore, the carbon concentration of the crystal can be controlled only by the CO concentration in the furnace gas.

Further, the problem that the carbon concentration becomes high when B ₂ O ₃ having a low water content is used is that after melting the polycrystal, it is kept in a furnace atmosphere having a constant CO concentration for a predetermined time or more, specifically, GaAs. In this case, the carbon concentration could be set to a predetermined value which was not too high by allowing the single crystal to be pulled after standing for 10 hours or longer, preferably 15 hours or longer.

That is, the present invention provides a method for growing a compound semiconductor single crystal by the LEC method, wherein the water content is 100%.
Using B ₂ O ₃ with a low water content of ppmw or less, controlling the CO concentration in the furnace atmosphere gas after melting the compound semiconductor polycrystal to a certain concentration and leaving it for a predetermined time or more, and then the furnace atmosphere gas A method for producing a compound semiconductor single crystal, which comprises growing a compound semiconductor single crystal while controlling the CO concentration therein to a constant concentration.

[0014]

EXAMPLE FIG. 4 shows an example of a single crystal growth apparatus used in the method of the present invention. In the crystal growth apparatus of this embodiment, a crucible 2 is rotatably supported by a support shaft 3 in a closed high-pressure pulling furnace 1, and a carbon heater 4 is provided around the crucible 2.
Are arranged. A heat shield 5 also made of carbon is arranged outside the heater 4, and
A pulling shaft 6 having a seed crystal at the lower end from above the crucible 2
Is hanging. Further, a gas introduction pipe 11 for introducing an inert gas and the like and an exhaust pipe 12 for exhausting the gas in the furnace are connected to the side wall of the pulling furnace 1, and the inside of the furnace is provided in the middle of the gas introduction pipe 11. The pressure regulating valve 13 and the exhaust pipe 12
A valve 14 is provided midway.

A CO gas concentration detector 16 is connected to the exhaust pipe 12, and a control device 17 controls the valve 14 based on an output signal of the detector 16. An inert gas cylinder and a CO or CO ₂ or oxygen cylinder are connected to the starting end of the gas introduction pipe 11 and are switchable.

First, 7N (9
7N (99.
99999%) high purity As and 6 inch diameter pBN
Put it in a crucible, put B ₂ O ₃ as a sealant on it,
It was set in the high-pressure pulling furnace. B ₂ O ₃ has a water concentration of 50 pp
The mw one was used. After the inside of the high-pressure pulling furnace was replaced with Ar gas, a pressure of 30 kg / cm ² was applied, the temperature was raised to about 500 ° C., B ₂ O ₃ was melted, and the temperature was raised to 600-700 ° C. Crystals were synthesized. 1400 in the furnace as it is
After further raising the temperature to 0 ° C. to melt the GaAs polycrystal, set the secondary pressure of the furnace pressure control valve 13 of the gas introduction pipe 11 to 20 kg / cm ² , and open the valve 14 of the exhaust pipe 12. The pressure inside the high-pressure pulling furnace is gradually reduced to 20 kg / cm ² , the valve 15 is opened, the CO gas concentration is measured by the detector 16, and the CO gas concentration is controlled to a constant value. A seed crystal was added to the melt in the crucible while keeping the gas concentration constant and GaAs was added.
Single crystal pulled up.

CO concentrations of 100 ppm, 300 ppm, and 6 respectively
Fig. 3 shows the carbon concentration of the crystal when controlled to be constant at 00 ppm.
Shown in. As shown in FIG. 3, it was possible to obtain a constant single crystal up to the tail at an arbitrary carbon concentration depending on the CO concentration. The carbon concentration was analyzed by the IR absorption method, and the conversion factor was 9.2 × 10 ¹⁵ cm ⁻¹ .

[0018]

As described above, in the method for producing a compound semiconductor single crystal by the LEC method, 100 ppmw
The following low B ₂ O ₃ concentration was used to control the CO concentration in the furnace atmosphere gas after melting the compound semiconductor polycrystal to a constant concentration and leave it for a predetermined time or longer, and then in the furnace atmosphere gas By growing a compound semiconductor single crystal while controlling the CO concentration in the same manner to a constant concentration, the carbon concentration of the crystal is controlled only by the CO concentration in the gas without being affected by the change in the water concentration of B ₂ O _3. I was able to.

[Brief description of drawings]

FIG. 1 shows variations in carbon concentration in the growth axis direction of a GaAs single crystal grown by a conventional method.

FIG. 2 shows changes in water concentration of B ₂ O ₃ during crystal growth.

FIG. 3 shows variations in carbon concentration in the growth axis direction of a GaAs single crystal grown by the method of the present invention.

FIG. 4 is a single crystal pulling apparatus to which the method of the present invention is applied.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Soichiro Otani 3-17-35, Niizonan, Toda City, Saitama Prefecture Japan Mining Co., Ltd.

Claims (1)

[Claims] 1. A method for growing a compound semiconductor single crystal by the LEC method, wherein B ₂ O ₃ having a low water content of 100 ppmw or less is used, and CO in the atmosphere gas in the furnace after melting the compound semiconductor polycrystal is used. A compound semiconductor single crystal characterized by growing a compound semiconductor single crystal while controlling the CO concentration in a furnace atmosphere gas to a constant concentration after controlling the concentration to be a constant concentration for a predetermined time or more. Production method.