JPH1129399A - Method and apparatus for producing GaAs single crystal - Google Patents

Abstract

(57) Abstract: When selectively introducing a gas containing no CO and a gas containing CO into a pressure vessel by opening and closing a valve, the gas is caused by a high-speed rush of gas generated when the valve is opened. Variations in the calorific value of the heater are eliminated, and the carbon concentration in the GaAs single crystal is kept constant in the growth direction. When manufacturing a GaAs single crystal by a liquid sealing pulling method, valves provided in two gas introduction systems according to a concentration of carbon monoxide in an atmospheric gas in a pressure vessel are provided. 18 to control the opening and closing of the first gas cylinder 1
9, an Ar gas containing no CO gas is selectively introduced into the pressure vessel 9 from the second gas cylinder 20. Pressure vessel 9 into which this gas is introduced
When the gas is introduced into the pressure vessel 9, the gas is dispersed to reduce the flow velocity, thereby preventing high-speed intrusion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a GaAs single crystal, which is a compound semiconductor, by a liquid sealing and pulling method (hereinafter abbreviated as LEC method), and an apparatus therefor.

[0002]

2. Description of the Related Art GaAs single crystals are widely used as substrates for high-speed high-frequency devices such as magnetoelectric transducers, field-effect transistors (FETs), integrated circuits (ICs), and large-scale integrated circuits (LSIs). One of the methods for producing a single crystal of a substrate material used for these devices is the LEC method.

In the production of a GaAs single crystal by the LEC method, Ar or N ₂ gas is used as an inert gas, and the crystal is grown by heating after pressurization.
It is mixed as an impurity into the s crystal. The carbon mixed into the GaAs crystal becomes a shallow acceptor, and the electrical characteristics of the GaAs single crystal greatly change depending on the concentration. On the other hand, the electrical characteristics required for a GaAs wafer are GaAs
The wafer varies depending on the type of device used as the substrate. For this reason, it is desirable that the concentration of carbon contained in the GaAs single crystal has as small a variation as possible with respect to a desired carbon concentration and is uniform from the front end to the rear end of the crystal. There is also a need for a method of growing such a GaAs single crystal with good reproducibility.

[0004] Carbon mixed into the GaAs single crystal by the LEC method is supplied from carbon monoxide in an atmosphere gas during the crystal growth. Therefore, by controlling the concentration of carbon monoxide in the furnace during crystal growth, that is, in the pressure vessel 34, to a predetermined value,
A method has been used in which the concentration of carbon contained in a single crystal is adjusted to a desired value.

FIG. 4 shows a configuration of a conventional GaAs single crystal manufacturing apparatus using the above-described LEC method. A crucible 31 made of pBN (pyrolytic boron nitride) is rotatably supported by a crucible support shaft 32 in a pressure vessel 34, and the raw material Ga and As are contained in the crucible 31, and a liquid sealant is placed thereon. Then, the inside of the pressure vessel 34 is evacuated through an exhaust gas pipe 46 and a valve 47 by an exhaust device (not shown) provided outside, with B ₂ O ₃ having low reactivity with the raw material element. After the evacuation, a first gas cylinder (Ar gas cylinder) 44 and a valve 42 or a second
Ar gas as an inert gas or Ar gas mixed with CO gas is introduced at a predetermined pressure from a gas cylinder (Ar gas cylinder mixed with CO gas) 45 through a valve 43 and a gas introduction pipe 41.

[0006] Thereafter, the GaAs melt 30 is produced by heating with a heater 33 located on the outer periphery of the crucible 31. At this time, the GaAs melt 30 is melted B ₂ O
Coated with ₃ . Thereafter, the seed crystal 27 provided at the lower end of the crystal pulling shaft 26 is brought into contact with the liquid surface of the GaAs melt 30, and the seed crystal 27 is gradually pulled up and pulled up while controlling to a predetermined diameter. GaAs single crystal 28 is obtained. In addition, 35 to 40 are heat insulating materials.

The control of the carbon monoxide concentration CO is performed as follows. The atmosphere gas in the pressure vessel 34 is led to a CO concentration measuring device 49 outside the furnace through a gas pipe 48, and the CO gas concentration in the pressure vessel 34 is monitored by the CO concentration measuring device 49.
In the case where the CO gas concentration in the gas container 4 is high, an inert gas (Ar gas) containing no CO gas is supplied from the first gas cylinder 44 through the valve 42 and the gas introduction pipe 41 to the pressure vessel 34.
The gas concentration in the pressure vessel 34 is reduced by introducing the gas into the pressure vessel 34 and discharging the gas in the pressure vessel 34 through the exhaust gas pipe 46 and the valve 47. When the CO gas concentration in the pressure vessel 34 is lower than a predetermined value, a second gas cylinder (an Ar gas cylinder containing CO gas) is used.
45 through a valve 43 and a gas introduction pipe 41,
Inert gas mixed with O gas (Ar gas mixed with CO gas)
Is introduced into the pressure vessel 34, and the gas in the pressure vessel 34 is discharged through the exhaust gas pipe 46 and the valve 47 to increase the CO gas concentration in the pressure vessel 34.

[0008]

In the single crystal pulling apparatus used in the conventional manufacturing method, when gas is introduced into the pressure vessel 34, the terminal opening of the gas introduction pipe 41 from the gas cylinders 44 and 45 is connected to the pressure vessel 34. The valve 42 or 43, which had been closed until then, is instantaneously opened according to the concentration of carbon monoxide in the pressure vessel, and the high-pressure gas from the gas cylinder 44 or 45 is opened. At high speed into the pressure vessel 34.

However, when the gas enters the pressure vessel at a high speed, the atmosphere in the pressure vessel is disturbed, the calorific value of the heater 33 greatly changes, and the temperature of the GaAs melt 30 greatly fluctuates. there were.

When a large change in the calorific value of the heater occurs,
The control of the diameter of the GaAs single crystal is disturbed, and it becomes difficult to grow the GaAs single crystal with good reproducibility. Further, when the temperature of the GaAs melt fluctuates, the amount of CO gas mixed from the atmospheric gas into the raw material melt changes, making it difficult to keep the carbon concentration in the GaAs single crystal constant in the growth direction.
This leads to uneven electrical properties of the wafer.

In order to prevent the gas from entering the pressure vessel at a high speed, the on-off valve is not turned on / off.
Although it is conceivable to control the gas introduction amount by changing the opening of the flow control valve, it cannot be adopted because the responsiveness is deteriorated.

Therefore, an object of the present invention is to solve the above-mentioned problems, eliminate large fluctuations in the calorific value of the heater during gas introduction, and prevent large temperature fluctuations in the GaAs melt, thereby improving the reproducibility of the GaAs single crystal. Well grown, GaAs
An object of the present invention is to provide a method and an apparatus for manufacturing a GaAs single crystal capable of keeping the carbon concentration in the single crystal constant in the growth direction.

[0013]

Means for Solving the Problems In order to achieve the above object, the present invention is configured as follows.

The method for producing a GaAs single crystal of the present invention
In producing an aAs single crystal by the liquid sealing pulling method, the valves provided in the two gas introduction systems are controlled to open and close according to the concentration of carbon monoxide in the atmospheric gas in the pressure vessel, and the two gas introduction systems are used. Manufacture of a GaAs single crystal in which the concentration of carbon contained in a GaAs single crystal is controlled by selectively introducing an inert gas containing no carbon monoxide gas and an inert gas mixed with carbon monoxide gas into a pressure vessel. In the method, when the inert gas not containing the carbon monoxide gas and the inert gas mixed with the carbon monoxide gas are introduced into the pressure vessel, the flow rate of the gas is reduced.

Further, in the GaAs single crystal manufacturing apparatus of the present invention, a GaAs melt and a liquid sealant covering the upper surface of the melt are accommodated in a pressure vessel pressurized with an inert gas, and heated by a heater. An apparatus for manufacturing a GaAs single crystal by installing a crucible and bringing up a GaAs single crystal seed crystal while rotating the seed crystal while contacting the upper surface of the GaAs melt,
A carbon monoxide concentration measuring means for measuring the concentration of carbon monoxide in the pressure vessel; and introducing an inert gas containing no carbon monoxide gas and an inert gas containing carbon monoxide gas.
In order to selectively introduce into the pressure vessel an inert gas not containing carbon monoxide gas and an inert gas mixed with carbon monoxide gas, which are provided in two gas introduction systems and two gas introduction systems, respectively. An on-off valve that is controlled to open and close according to the measurement result of the carbon monoxide concentration measuring means, and a carbon monoxide gas that is provided at a gas inlet of a pressure vessel to which two gas introduction systems are connected and is introduced into the pressure vessel. A speed reducing means for reducing the flow rate of the inert gas containing no gas and the inert gas mixed with the carbon monoxide gas.

The carbon concentration represented by the number of carbon atoms substituted for As lattice points in the grown GaAs single crystal is, for example, 1 × 10
^{When the} resistivity is suppressed to the range of ^{15 to} 5 × 10 ¹⁶ / cm ³ , the specific resistance becomes 10
It is known that a semi-insulating property of ¹⁷ Ω-cm or more is secured. Therefore, the control of the concentration of carbon monoxide in the atmospheric gas in the pressure vessel is controlled such that the carbon concentration in the grown GaAs single crystal is obtained as a desired value in this range. For example, when it is desired to obtain 2 × 10 ¹⁵ / cm ³ as a desired value of the carbon concentration in the GaAs single crystal, the concentration of carbon monoxide in the atmosphere gas in the pressure vessel is set to a predetermined value of 500 ppm.
Is controlled so that

With respect to the desired value of the carbon concentration as described above, L
In order to reproducibly grow a GaAs single crystal having a small carbon concentration variation from the front end to the rear end of the GaAs single crystal grown by the EC method, two gases are introduced according to the concentration of carbon monoxide in the atmosphere gas in the pressure vessel. A valve provided in the system is controlled to open and close, and an inert gas containing no carbon monoxide gas and an inert gas mixed with carbon monoxide gas are selectively introduced into the pressure vessel from the two gas introduction systems.

Since the introduction of the inert gas into the pressure vessel is performed by opening and closing control of the valve, that is, on / off control, when the valve is opened, the gas enters the pressure vessel at a high speed. . When the gas enters the pressure vessel at a high speed, the atmosphere in the pressure vessel is disturbed, the calorific value of the heater changes greatly, and a large temperature fluctuation occurs in the GaAs melt.

The present invention reduces the flow rate of the gas introduced into the pressure vessel and disturbs the atmosphere in the pressure vessel in order to eliminate such a change in the calorific value of the heater and the fluctuation in the temperature of the GaAs melt. It is to suppress.

The deceleration means for reducing the gas flow velocity is, for example, fitting a cap made of a porous substance such as graphite into a gas inlet in a pressure vessel and dispersing the gas through the pores of the porous substance. This can be achieved by adopting a configuration.

When the flow rate of the gas introduced into the pressure vessel is reduced at the gas introduction port by passing through a speed reducing means such as a graphite cap as described above, gas intrusion is reduced, and the atmosphere in the pressure vessel is reduced. It is suppressed from being disturbed,
The phenomenon that the heating value of the heater greatly changes is eliminated, and Ga
No large temperature fluctuation occurs in the As melt. Therefore, G
An aAs single crystal can be grown with good reproducibility, and the carbon concentration in the GaAs single crystal can be kept constant at a desired value in the growth direction.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a structure of a single crystal pulling apparatus as a crystal growth furnace used for carrying out the present invention.

As shown in FIG. 1, pBN is
The crucible 6 is rotatably supported and installed by a crucible support shaft 7, a heater 8 is arranged around the crucible 6, and further, heat insulating materials 10 to 12 are arranged around the outside.
Insulating materials 13 to 15 are also arranged between the pressure vessel 9 and the bottom.

The interior of the pressure vessel 9 is connected to an exhaust device (not shown) provided outside through an exhaust gas pipe 21 and a valve 22. Further, it is connected to a first gas cylinder 19 which is an Ar gas cylinder through a gas introduction pipe 16 and a valve 17, and is connected to a gas introduction pipe 16.
And a valve 18 connected to a second gas cylinder 20 which is an Ar gas cylinder containing CO gas. This second
5% CO gas in argon gas
Contains mixed gas. The inside of the pressure vessel 9 is connected to a CO concentration measuring device 24 outside the furnace through a gas pipe 23.

A pipe from the gas introduction pipe 16 to the first gas cylinder 19 constitutes a first gas introduction system 51, and a pipe from the gas introduction pipe 16 to the second gas cylinder 20 is a second gas introduction system. 52.

Here, in the conventional configuration in which the terminal opening of the gas introduction pipe 16 from the gas cylinders 19 and 20 is directly opened and communicated with the pressure vessel 9, Ar gas or mixed gas from the gas cylinders 19 and 20 is supplied to the pressure vessel. 9 is introduced directly into the heater 8 when the gas is introduced due to the introduction of the gas.
Of the GaAs melt 5 greatly fluctuates and the temperature of the GaAs melt 5 fluctuates greatly.

In order to avoid such inconvenience, the single crystal pulling apparatus shown in FIG.
A graphite cap 25 is attached to an inlet through which a gas is introduced at a connection portion between the pressure vessel 9 and the gas introduction port 9 a in the pressure vessel 9. In this embodiment,
The gas inlet 9a is provided at the lower part of the outer peripheral portion of the pressure vessel 9. A cap 25 made of graphite covers the gas inlet 9a from the inside of the pressure vessel 9 so as to cover the pressure vessel 9.
Is provided between the inner side surface of the heat sink and the heat insulating material 13. Graphite is a porous substance and has air permeability. By attaching the graphite cap 25 to the gas introduction inlet, the flow rate of the gas introduced into the pressure vessel 9 is reduced.

(Example) Ten GaAs single crystals were grown in the following manner using the single crystal pulling apparatus having the above structure.

The raw material Ga and As are accommodated in the crucible 6 and B ₂ O having low reactivity with the raw material element is formed thereon as a liquid sealant.
₃ covered with, after evacuating the pressure vessel 9 via the exhaust gas gas pipe 21 and the valve 22 by the exhaust apparatus provided outside, inside the pressure vessel 9, the first from the gas cylinder 19 valve 17 and the gas introduction pipe 16 Ar gas, which is an inert gas, is introduced at a predetermined pressure of 20 kg / cm ² .
Thereafter, the GaAs melt 5 is produced by heating with a heater 8 located at the outer peripheral portion of the crucible 6. At this time, the GaAs melt 5 is covered with molten B ₂ O _{3 as the} liquid sealant 4.

As described above, under a pressure of 20 kg / cm ₂ , the crucible 6 is filled with the GaAs melt 5 having an excess composition of As.
After producing 0 kg, the CO gas concentration in the space where the crystal is pulled up is set to a predetermined value of 50 by opening and closing the valves 17 and 18.
It was adjusted to 0 ppm. That is, the atmospheric gas in the pressure vessel 9 is passed through the gas pipe 23 and the CO concentration
4 and the pressure vessel 9 is measured by the CO concentration measuring device 24.
Monitor the concentration of CO gas in
If the CO gas concentration in the pressure vessel 9 is higher than
An inert gas (Ar gas) containing no O gas is introduced from the first gas cylinder 19 into the pressure vessel 9 through the valve 17 and the gas introduction pipe 16, and the gas in the pressure vessel 9 is discharged into the exhaust gas pipe 21. And, by discharging through the valve 22, the CO gas concentration in the pressure vessel 9 was reduced.

When the CO gas concentration in the pressure vessel 9 is lower than a predetermined value of 500 ppm, the second gas cylinder 20 passes through the valve 18 and the gas introduction pipe 16
An inert gas mixed with CO gas (Ar gas mixed with 5% of CO gas) is introduced into the pressure vessel 9 and the pressure vessel 9
The CO gas concentration in the pressure vessel 9 was increased by discharging the gas inside through the exhaust gas pipe 21 and the valve 22.

While controlling the CO gas concentration in the pressure vessel 9 as described above, the seed crystal 2 provided at the lower end of the crystal pulling shaft 1 is controlled.
Was brought into contact with the GaAs melt 5 and the seed crystal 2 was gradually pulled up and pulled up while controlling to a predetermined diameter to obtain a GaAs single crystal 3.

At this time, the pressure in the space in which the GaAs single crystal is pulled up and the pressure in the heating space in which the heater 8 is installed are set to 20 kg / cm ² , respectively, and the carbon concentration in the GaAs crystal is set to a desired value of 2.0 × 10 2. Seed crystal 2 aiming at ¹⁵ / cm ³
Was applied to the GaAs melt 5 and the diameter was 110 mm and the length was 350
A GaAs single crystal 3 of mm was grown. Thus, Ga
Ten As single crystals 3 were pulled up.

Table 1 shows the results of the growth of a total of ten GaAs single crystals pulled up by the method of Example 1. In the case of the method of Example 1, single crystals were all grown, and generation of polycrystals was not observed.

[0036]

[Table 1]

Comparative Example A GaAs single crystal was grown using a conventional single crystal pulling apparatus shown in FIG.

In the second gas cylinder 45, C is added to Ar gas.
A gas containing 5% of O gas is contained. 20kg / cm ²
After preparing 20 kg of the GaAs melt 30 such that the As composition becomes excessive in the crucible 31 made of pBN under the above pressure, the valves 42 and 43 are opened and closed, and the first gas cylinder 44 from the first gas cylinder 44 is placed in the pressure vessel 34. A single Ar gas and an Ar gas containing a carbon monoxide gas from the second gas cylinder 45 are selectively introduced so that the concentration of the carbon monoxide gas in the pressure vessel 34 becomes a predetermined value of 500 ppm. .

Thereafter, as in the first embodiment, the pressure in the space in which the GaAs single crystal is pulled up and the pressure in the heating space in which the heater 33 is installed are each set to 20 kg / cm ² , and the carbon concentration of the GaAs single crystal is set to the desired value of 2 kg / cm 2. Aiming at 0.010 ¹⁵ / cm ³ , the seed crystal 27 was applied to the GaAs melt 30,
A GaAs single crystal 28 having a diameter of 110 mm and a length of 350 mm was grown. Thus, ten GaAs single crystals 28 were pulled up.

Table 2 shows the results of the growth of a total of 10 single crystals pulled up by the method of the comparative example.

[0041]

[Table 2]

(Comparison between Example and Comparative Example) According to the manufacturing method of the comparative example, as shown in Table 2, only 5 out of 10 lines are single crystals and the other 5 lines are polycrystals. Was. The position where the polycrystal was generated was not constant, and the shape of the crystal was disturbed.

On the other hand, in the case of the manufacturing method of the above embodiment,
As already mentioned in Table 1 above, all the ten grown crystals were all single crystals. Therefore, the manufacturing method of the example is superior to the manufacturing method of the comparative example in that it is an excellent GaAs that can stably grow a single crystal having no disorder in crystal shape.
It can be seen that this is a method for producing a single crystal.

Next, in order to measure the carbon concentration distribution in the grown GaAs single crystal, crystals were randomly selected one by one from the GaAs single crystals grown by the manufacturing method of the above embodiment and the comparative example. A sample having a thickness of 5 mm was taken from each position of every 20 mm from the front end (seed) to the rear end (tail) of each crystal, and both surfaces of each sample were polished to a mirror surface. Thereafter, the carbon concentration in the GaAs single crystal of each sample was measured by an infrared absorption method.
The distribution of the carbon concentration in the As single crystal was examined.

The results are shown in FIG. 2 and FIG. In the GaAs single crystal grown by the method of the comparative example (FIG. 3), each time gas enters, the effect appears as a large change in the carbon concentration, whereas the GaAs single crystal grown by the method of the example ( In the case of FIG. 2), since the gas intrusion is reduced, the deviation of the carbon concentration in the GaAs single crystal from the desired value (2 × 10 ¹⁵ / cm ³ ) is small.

[0046]

According to the method of the present invention, the flow rate of the gas introduced into the pressure vessel is reduced by opening the valve so that the atmosphere in the pressure vessel is not disturbed. Therefore, a large temperature fluctuation does not occur in the GaAs melt. Therefore, compared to the conventional method in which the gas flow rate at the time of introduction is not reduced, a single crystal having no disorder in the crystal shape is stabilized, and a crystal having a small carbon concentration with respect to a desired carbon concentration is stabilized. Can be manufactured. As a result, GaAs single crystals having more uniform electric characteristics can be produced at lower cost, and the manufacturing cost of an element using these as a substrate can be reduced.

According to the apparatus of the present invention, the above-mentioned effect can be appropriately obtained by the structure in which the gas introduction port of the pressure vessel is provided with the speed reducing means for reducing the gas flow rate.

In particular, when the speed-reducing means is constituted by a cap made of a porous substance, it can be realized by a simple structure in which the porous cap is fitted to the gas inlet of the pressure vessel.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a single crystal pulling apparatus used in a manufacturing method of an embodiment.

FIG. 2 is a view showing a carbon concentration distribution in a growth direction of a GaAs single crystal grown by a manufacturing method of an embodiment to obtain a crystal having a carbon concentration of 2.0 × 10 ¹⁵ / cm ³ .

FIG. 3 is a diagram showing a carbon concentration distribution in a growth direction of a GaAs single crystal grown by a conventional manufacturing method to obtain a crystal having a carbon concentration of 2.0 × 10 ¹⁵ / cm ³ .

FIG. 4 is a diagram showing a configuration of a single crystal pulling apparatus used in a manufacturing method of a comparative example.

[Explanation of symbols]

Reference Signs List 1 crystal pulling shaft 2 seed crystal 3 GaAs single crystal 4 liquid sealant 5 GaAs melt 6 crucible made of pBN 8 heater 9 pressure vessel 9a gas inlet 16 gas introduction pipe 17, 18 valve 19 first gas cylinder (Ar gas cylinder) ) 20 second gas cylinder (Ar gas cylinder mixed with CO gas) 24 CO concentration measuring device

Claims (3)

[Claims] In producing a GaAs single crystal by a liquid sealing pulling method, valves provided in two gas introduction systems are controlled to open and close according to the concentration of carbon monoxide in an atmospheric gas in a pressure vessel. By selectively introducing an inert gas containing no carbon monoxide gas and an inert gas containing carbon monoxide gas into the pressure vessel from two gas introduction systems, the carbon concentration contained in the GaAs single crystal is controlled. In the method for producing a GaAs single crystal, when introducing the inert gas containing no carbon monoxide gas and the inert gas mixed with carbon monoxide gas into the pressure vessel, the flow rate of the gas is reduced. A method for producing a GaAs single crystal, comprising: 2. A pressure vessel pressurized with an inert gas contains Ga.
A crucible containing the As melt and a liquid sealant covering the upper surface of the melt is placed by heating with a heater, and the GaAs single crystal is brought into contact with the upper surface of the GaAs melt and pulled up while rotating. In an apparatus for producing a single crystal, a carbon monoxide concentration measuring means for measuring a carbon monoxide concentration in a pressure vessel, and an inert gas containing no carbon monoxide gas and an inert gas mixed with carbon monoxide gas are used. Two gas introduction systems for guiding each gas, and an inert gas containing no carbon monoxide gas and an inert gas mixed with carbon monoxide gas, which are provided in each of the two gas introduction systems, are selectively introduced into the pressure vessel. In order to achieve this, an opening / closing valve that is controlled to open and close according to the measurement result of the carbon monoxide concentration measuring means, and a gas introduction port of a pressure vessel to which two gas introduction systems are connected, are introduced into the pressure vessel. Apparatus for producing a GaAs single crystal and a decelerating means for decelerating the flow rate of the entrained inert gas of the inert gas and carbon monoxide gas containing no carbon monoxide gas. 3. The apparatus for producing a GaAs single crystal according to claim 2, wherein said deceleration means is constituted by a cap made of a porous substance fitted to a gas inlet of a pressure vessel.