JPH0891990A - Production of semi-insulating gallium-arsenic single crystal - Google Patents

Abstract

PURPOSE: To obtain a semi-insulating GaAs single crystal, hardly changing the carbon concentration and good in uniformity even in the case of a crystal in a continuous length. CONSTITUTION: This method for producing a semi-insulating GaAs single crystal is to bring a seed crystal 2 into contact with a GaAs melt 5 placed in a crucible 7 and pull up the single crystal 3 in a pulling up furnace 20 in a prescribed atmosphere according to a liquid-encapsulated Czochralski method. The pulling up furnace 20 is equipped with a gas introduction port 12 for continuously introducing a gas at a prescribed flow rate into the furnace in the lower part of the pulling up furnace 20. Further, a discharge port 13 for continuously discharging the atmospheric gas in the furnace at the same flow rate as that of the introduced gas is installed in the upper part of the pulling up furnace 20. Mass flow controllers 14 are respectively provided in the introduction port 12 and the discharge port 13 to control the introduced gas and the discharge gas at the prescribed flow rates. Thereby, the carbon concentration in the resultant crystal is controlled constant without causing a disturbance in a redox reactional system.

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 semi-insulating GaAs single crystal, and more particularly to a method for controlling carbon which is a main impurity in a long crystal.

[0002]

2. Description of the Related Art When manufacturing an electronic device using a GaAs single crystal, a GaAs single crystal is sliced into a thin wafer and the surface thereof is polished to a mirror surface. G
The aAs substrate itself may be used as an electron channel layer, or a substance having another composition may be grown on the substrate to form a channel layer. In either case, a large number of very small elements are formed on the substrate, and the substrate characteristics affect the elements. Therefore, the uniformity of the characteristics of the entire substrate is important.

When the GaAs substrate itself is used as an electron channel layer, a method of implanting impurity ions serving as donors into the substrate and then activating it by heat treatment is generally used, and as a crystal, the concentration of carbon acting as an acceptor can be controlled. is important. On the other hand, when a substance having another composition is grown on the substrate to form a channel layer, it is necessary to suppress the current leakage on the substrate side, and it is important to control the carbon concentration that controls the resistance of the substrate. Thus, the carbon in the crystal plays an important role in all cases.

Generally, a semi-insulating GaAs single crystal is produced by a liquid sealing pulling method. At that time, it is well known that carbon is taken into the crystal from CO gas generated from graphite used as a member in the furnace (for example, PJ
Doering et.al., "Semi-insulating III-V Materials, 19
90 ", etc. That is, residual water in the furnace, oxygen reacts with graphite to generate CO gas, which reacts with boron trioxide as a sealant, and further reacts with melt to melt. Are incorporated into the crystal and are incorporated into the crystal as carbon when the crystal is solidified.

Further, as reported in the above document, it is well known that the CO gas concentration in the furnace and the carbon concentration in the crystal have a positive correlation. Ideally, the carbon concentration in the crystal should be constant. For that purpose, a method is generally used in which the concentration of CO contained in the atmosphere gas during crystal growth is kept constant.

However, the crystal does not directly react with the CO gas, but is taken into the crystal as carbon after undergoing an oxidation-reduction reaction between the CO gas, boron trioxide and the melt, so that the CO concentration and the carbon concentration are different from each other. Is relatively weak. As the growth time becomes longer, the effect of the redox reaction becomes stronger than the effect of the CO concentration. For this reason,
The method of keeping the CO concentration constant is restricted to the growth of relatively short crystals.

It is considered that a GaAs single crystal cannot be single-crystallized into a long crystal of 1 m class such as a Si crystal produced by a similar pulling method, and a relatively short crystal (20 ~ 25 cm) was produced. The growth time of such a short crystal is about one day, and the carbon concentration control method by the above-described method of keeping the CO concentration constant has been put to practical use.

[0008]

However, recently, it has become possible to grow a long GaAs single crystal as long as a Si crystal.
Since the growth time has also become long, 3 to 4 days, the conventional CO
There is a problem that cannot be controlled by the constant concentration method.

For example, for a short crystal of 25 cm, CO in the furnace
Almost no correlation is found between the concentration and the carbon concentration in the crystal. However, in the case of a long crystal of 50 cm or more, if the CO concentration is kept constant and grown, the concentration usually increases especially on the tail side,
The uniformity tends to deteriorate. Therefore, it has been desired to develop a new method capable of uniformly controlling the carbon concentration even in such a long crystal.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method for producing a semi-insulating GaAs single crystal having a long carbon with a small change in carbon concentration and good uniformity.

[0011]

Means for Solving the Problems Semi-insulating GaA of the present invention
The method for producing an s single crystal is the same as the method for growing a semi-insulating GaAs single crystal by the liquid encapsulation pulling method, in which a certain amount of an inert gas is continuously introduced into the furnace during crystal growth, and The carbon concentration in the crystal is controlled by continuously discharging the atmospheric gas in the same amount as the amount of the introduced gas.

[0012]

When the correlation between the CO concentration in the furnace and the carbon concentration in the crystal is classified according to the crystal part (seed side, middle side, tail side), the CO concentration and the carbon concentration are relatively high at each part. It turns out that a strong correlation is seen. Therefore, if the CO concentration is controlled according to each part, the carbon concentration should be controlled to be constant.

However, as described above, the carbon concentration in the crystal is not limited to the CO gas concentration, but also the growth time, the redox reaction constant in boron trioxide, the reaction temperature, the redox reaction constant in the melt, Since it is a correlation system with various factors such as reaction temperature, it is extremely difficult and unrealistic to control the CO concentration under conditions suitable for each site.

Then, what was invented as a realistic and simple method is the method of the present invention for replacing a certain amount of gas in the furnace. That is, a certain amount of gas is continuously introduced into the furnace during crystal growth, and the atmospheric gas in the furnace is continuously discharged in the same amount as the amount of introduced gas. This is a method of controlling the carbon concentration in the crystal by gradually lowering the CO concentration.

According to this method, the CO concentration at the site can be adjusted to an appropriate CO concentration as it grows toward the tail side in a stable state without disturbing the redox reaction system, and as a result, the carbon concentration in the crystal can be increased. It can be controlled uniformly.

The gas introduced into the furnace may be a gas containing a halogen compound of Ga or As, an organometallic compound, or a hydride, but an inert gas such as Ar or N ₂ is preferable. This is not only because an inert gas is generally used for GaAs crystal growth, but also because it does not disturb the redox reaction system. The amount of introduced gas and the amount of discharged gas are preferably controlled by the flow rate per unit time.
Although a simple flow meter or constant flow valve can be used to control the flow rate of the introduced gas and the exhaust gas, a mass flow controller should be used to prevent disturbance to the redox reaction system. preferable.

[0017]

EXAMPLE FIG. 1 is a schematic view of an internal structure example of a pulling furnace 20 by a liquid sealing pulling method for carrying out a method of manufacturing a semi-insulating GaAs single crystal.

Reference numeral 11 denotes a stainless steel inner wall of the pulling furnace 20. The PBN crucible 7 has a crucible shaft 8 in the center of the pulling furnace 20.
It is rotatably supported by. A heater 6 is provided on the outer circumference of the crucible 7, and the heater 6 is divided into upper, middle, and lower three parts, and an appropriate solid-liquid interface shape can be controlled by changing the output balance of each heater. A graphite heat insulating member 9 is provided in a cylindrical shape on the outer circumference of the heater 6 to keep the hot zone warm. A graphite upper heat insulating member 10 is further extended above the graphite heat insulating member 9 in order to keep the crystal temperature at an appropriate temperature.

A GaAs raw material and a block of boron trioxide which is a sealant are put in the crucible 7, which are heated and melted by the heater 6 to melt the GaAs melt 5 and a liquid state which covers the surface of the GaAs melt 5. Boron trioxide 4 is obtained. To produce a single crystal, the seed crystal 2 attached to the lower end of the pulling shaft 1 is brought into contact with the GaAs melt 5 to pull up the GaAs single crystal 3.

Below the pulling furnace 20, the pulling furnace 2 is provided.
A gas inlet 12 for introducing a gas, for example, an inert gas such as Ar or N ₂ is provided in 0, and the gas inlet 12 is
A simple flow meter, constant flow valve, or mass flow controller 14 is provided to continuously introduce a fixed amount of gas into the furnace during crystal growth. In addition, a gas discharge port 13 for discharging the atmospheric gas in the furnace is provided in the upper part of the pulling furnace 20,
The gas outlet 13 is provided with a simple flow meter, a constant flow valve, or a mass flow controller 14 in order to continuously discharge the atmospheric gas in the furnace in the same amount as the introduced gas amount. The fixed amount, which is the amount of introduced gas and the amount of discharged gas controlled by the mass flow controller 14 and the like,
It is controlled by the amount per unit time.

As described above, when a certain amount of gas is continuously introduced into the furnace during crystal growth and the atmospheric gas in the furnace is continuously discharged in the same amount as the introduced gas, the furnace grows as the crystal grows. The CO concentration in the inside gradually decreases, and moreover, as the CO grows toward the tail side in a stable state without disturbing the redox reaction system, the appropriate CO concentration can be obtained in that portion. Therefore, even with a long GaAs crystal, the carbon concentration in the crystal can be controlled to be constant.

Next, a specific example of the method for producing the above-mentioned GaAs single crystal will be described.

Example 1 A GaAs single crystal was prepared using a pulling furnace having a pressure resistance of 100 atm. The capacity in the furnace is about 10
It is 0 liter. The members in the furnace are made of high-purity graphite. PBN crucible with a diameter of 28 cm, 6N grade high purity Ga135000g and As15000g
Is charged with boron trioxide 30 as a sealing agent.
00g was charged. This was set in a pulling furnace and directly synthesized, and then GaAs with a diameter of 80 mm was drawn by the pulling method.
A single crystal was grown to 800 mm. Atmosphere gas is Ar 20
Atm.

The CO concentration in the furnace at the start of growth is 5000 ppm
Met. From the start of growth, 0.5 liter / minute of Ar gas was introduced into the furnace, and at the same time, the furnace gas was discharged at the same flow rate. CO concentration in the furnace is about 3500ppm at the middle of growth
On the tail side immediately before the end of growth, it was about 2000 ppm. A 35 atm withstand pressure mass flow controller was used to control the flow rate of gas introduction and discharge.

The carbon concentration was measured at each of the seed, middle and tail portions of the obtained crystal, and was found to be 1 × 10.
It was confirmed that the uniformity was as high as ¹⁵ cm ^-3 .

(Example 2) In the same furnace as in Example 1, raw materials,
The growth conditions were the same, and the gas flow rates of introduction and discharge were controlled using a simple glass tube type flow meter.

The CO concentration in the furnace at the start of growth is 5000 ppm
Met. From the start of growth, 0.5 liter / minute of Ar gas was introduced into the furnace, and at the same time, the furnace gas was discharged at the same flow rate. The CO concentration in the furnace was about 3500 ppm at the intermediate point and about 2000 ppm on the tail side immediately before the growth was completed.

The carbon concentration of each of the seed, middle and tail portions of the obtained crystal was measured and found to be 1 ×, respectively.
10 ¹⁵ cm ^-3 , 0.95 x 10 ¹⁵ cm ^-3 , 0.95 x 10 ¹⁵
The result was cm ⁻³ , and although it did not reach the level of Example 1, satisfactory results were obtained. The reason why it was not possible to obtain such high uniformity as at the level of Example 1 is probably because the control accuracy of the flow meter was poor.

(Comparative Example 1) In the same furnace as in Example 1, raw materials,
By making the growth conditions the same and appropriately changing the gas flow rates of introduction and discharge, the CO concentration in the furnace was controlled to be constant at about 5000 ppm, and crystals of the same length were grown.

When the carbon concentration was measured at each of the seed, middle and tail portions of the obtained crystal, it was 1 × 1 each.
It was recognized that the ^values gradually increased to 0 ¹⁵ cm ⁻³ , 1.5 × 10 ¹⁵ cm ⁻³ , and 2 × 10 ¹⁵ cm ⁻³ .

(Comparative Example 2) In the same furnace as in Example 1, raw materials,
While keeping the growth conditions the same, and appropriately changing the gas flow rates of introduction and discharge, the CO concentration in the furnace was adjusted to about 5000, 3500, and 2000 pp at the seed, middle, and tail portions, respectively.
The crystal having the same length was grown by controlling so as to be m.

The carbon concentration of each of the seed, middle and tail sites of the obtained crystal was measured and found to be 1 × 1.
The uniformity was 0 ¹⁵ cm ⁻³ , 1.2 × 10 ¹⁵ cm ⁻³ , 1.1 × 10 ¹⁵ cm ^−3, and the uniformity as in Example 1 was not obtained. It is presumed that the redox reaction system is not as stable as in the examples.

(Other Embodiments) In the above embodiments, the semi-insulating GaAs single crystal is described, but the present invention is not limited to this. For example, it can be applied to the control of the in-furnace gas in other crystals, InP, GaP, etc., created by the liquid sealing pulling method.

This embodiment has the following advantages because a long GaAs single crystal having a practically high degree of uniformity can be manufactured.

(1) Since a crystal capable of obtaining a larger number of wafers can be formed with one labor of charging the raw material, there is an economical effect.

(2) The impurities in the crystal have a concentration distribution that correlates with the solidification rate due to the segregation phenomenon. When viewed in the crystal length direction, the longer the crystal, the smaller the change in concentration per unit length. The uniformity will be good. Therefore, it is possible to manufacture a wafer having a small difference in characteristics between the individual wafers. For this reason, a wafer having a target specification range can be manufactured with good controllability, which is highly economical.

[0037]

According to the present invention, a certain amount of gas is introduced into the furnace and the same amount of atmospheric gas is discharged to control the carbon concentration in the crystal. A single crystal with a small change in carbon concentration and good uniformity can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing the inside of a pulling furnace for carrying out a method for producing a GaAs single crystal of the present invention.

[Explanation of symbols]

 3 GaAs single crystal 5 GaAs melt 7 PBN crucible 12 gas inlet 13 gas outlet 14 mass flow controller 20 pulling furnace

Claims (3)

[Claims] 1. A method for producing a semi-insulating GaAs single crystal by a liquid-sealing pull-up method, wherein a certain amount of gas is continuously introduced into a furnace during crystal growth, and the atmosphere gas in the furnace is introduced as described above. A semi-insulating GaAs characterized by controlling the carbon concentration in the crystal by continuously discharging the same amount as the gas amount.
Method for producing single crystal. 2. The semi-insulating G according to claim 1, wherein the introduced gas is an inert gas such as Ar or N _2.
Method for producing aAs single crystal. 3. The method for producing a semi-insulating GaAs single crystal according to claim 1, wherein a mass flow controller is used to control the flow rates of the introduced gas and the exhaust gas.