JPH10297999A - Production of gallium-rsenic single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain large-diameter GaAs single crystal of high quality by providing a cooling process that increases the cooling rate of the GaAs single crystal, at the temperature of the GaAs single crystal becomes low, after the GaAs single crystal is formed. SOLUTION: A temperature gradient is formed between the high temperature zone and the low temperature zone and the GaAs starting melt 54 is moved from the high temperature zone to the low temperature zone, solidified to form GaAs single crystal. In this case, the temperature gradient is set <=50 deg.C/cm and the cooling rate of the GaAs single crystal is increased in the range the formula: dT/dt<=[820,000×exp -0.0039×(T+273.15)}]/D<2> , after the GaAs single crystal 56 is formed (D is the average diameter in cm in the case that the GaAs single crystal is assumed to be columnar, T is the surface temperature of the GaAs single crystal in deg.C and dT/dt gives the cooling rate of the surface temperature of the GaAs single crystal, when the surface temperature is at T deg.C, in deg.C/hour.

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 gallium arsenide (hereinafter referred to as "GaAs") single crystals.
In particular, it relates to a method for producing a large-diameter GaAs single crystal.

[0002]

2. Description of the Related Art GaAs, which is the most typical semiconductor as a group III-V compound semiconductor, has a higher mobility than Si which constitutes a semiconductor device which is widely used at present. Therefore, compound semiconductor devices made of GaAs are most expected as next-generation semiconductor devices that require high-speed operation and high-frequency operation. However, the performance of a GaAs semiconductor device greatly depends on the quality of a GaAs single crystal as a starting material, for example, crystal defects and purity. Therefore, GaA
In order for a semiconductor device consisting of
The production method of As single crystal becomes very important.

As a method of manufacturing a GaAs single crystal, for example, a liquid sealed Czochralski (LEC: Liquid Encapsu)
lation Czochralski method and vertical Bridgman (VB: V)
It is well known that there is a crystal growing method such as the ertical Bridgeman method. In order to make the GaAs single crystal have more excellent characteristics as a starting material, various improvement measures for these methods have been proposed as follows.

According to the LEC method, 141-1 of the 14th International Symposium on GaAs and Related Compounds
Page 44 (Proceedings of the 14th Int.Symp.GaAs and R
As disclosed in Elated Compounds, p141-p144), a GaAs single crystal having a diameter of 3 inches has been obtained by solving the heat transfer equation and designing the thermal history of the GaAs single crystal. At this time, the GaAs
It is understood that the single crystal is cooled at a substantially constant cooling rate of 20 to 30 ° C./hour. In addition, in the VB method, as disclosed in Japanese Patent Publication No. Hei 7-23275, the diameter of a point defect is 50 mm (approximately 50 mm) in order to prevent point defects from precipitating at dislocation sites and generating and growing new dislocations due to thermal stress. The cooling rate of the GaAs single crystal (2 inches) is kept almost constant in the range of 20 to 250 ° C./hour.

[0005]

However, the diameter of each of the GaAs single crystals obtained by the above-described method is 4 inches or less. This value of 4 inches is equivalent to 8 inches of Si that is currently used mainly for manufacturing semiconductor devices.
GaAs semiconductor devices are extremely disadvantageous for practical use of GaAs semiconductor devices from the viewpoint of manufacturing cost and mass production.

When the diameter of a GaAs single crystal is increased by the above-described method, a large temperature difference is likely to occur between the central portion and the peripheral portion of the large-diameter single crystal during cooling. As a result, the thermal stress based on the temperature difference becomes smaller due to the lower yield stress G
Crystal defects such as point defects and dislocations are liable to occur in non-negligible addition to aAs single crystal. Therefore, sufficient quality and the like of the GaAs single crystal having a large diameter have not yet been obtained.

Accordingly, an object of the present invention is to provide a method for producing a large-diameter GaAs single crystal having high quality.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a temperature gradient formed between a high-temperature portion higher than the melting point of GaAs and a low-temperature portion lower than the melting point of GaAs. A method of manufacturing a GaAs single crystal by forming a GaAs single crystal by relatively moving and solidifying a GaAs raw material melt from a high temperature part to a low temperature part;
After the formation of the aAs single crystal, a cooling step of substantially increasing the cooling rate of the GaAs single crystal as the temperature of the GaAs single crystal is reduced is provided, the temperature gradient is set to 50 ° C./cm or less, and the cooling rate dT / Dt in the formula (1): dT / dt ≦ [820000 × exp ｛−0.0039 × (T + 273.1
5)｝] / D ² [where D represents the average diameter (cm) of the straight body portion when the GaAs single crystal is formed into a columnar shape, T represents the temperature (° C.) of the surface of the GaAs single crystal, And dT / dt is Ga in the cooling step.
Cooling rate (° C.) when the surface temperature of the As single crystal is T
/ Hour).].

As a result, the cooling rate of the high-temperature GaAs single crystal is reduced, and as a result, thermal stress that causes slippage in conjunction with more severe thermal vibration than that of the low-temperature GaAs single crystal can be suppressed. In addition, as a result of increasing the cooling rate in the low-temperature GaAs single crystal, the thermal stress increases as compared with the high-temperature GaAs single crystal. However, since thermal vibration is suppressed, slip can be prevented from occurring. Thus, by balancing thermal stress and thermal vibration, the tendency for crystal defects such as dislocations to be introduced or multiplied is reduced, and a high-quality GaAs single crystal can be obtained. This is particularly noticeable in a GaAs single crystal having a large shape in which a temperature distribution in the radial direction is easily formed during cooling.

In particular, the reason why the temperature gradient is set to 50 ° C./cm or less is to suppress the introduction of crystal defects and the formation of amorphous GaAs during the solidification of the GaAs raw material melt. In this way, the cooling rate can be quantified to precisely control the cooling step, and a GaAs single crystal of uniform quality can be manufactured.

Further, in the present invention, in order to suppress the precipitation of As as much as possible, the temperature of the low-temperature portion is set to 1000 ° C. or more, and the cooling rate in the cooling step is set to 900 ° C. ≦ T ≦ 1000 ° C.
In this case, the temperature is preferably set to 20 ° C./hour or more. This is because the present inventors have found that when the temperature of the GaAs single crystal surface is 900 to 1000 ° C., the precipitation of As becomes remarkable.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

FIG. 1 is a block diagram showing one embodiment of an apparatus useful for carrying out the method for producing a GaAs single crystal of the present invention. The illustrated device is a device used for the so-called vertical Bridgman method, and is an airtight container 10 provided with a temperature gradient.
A vertically elongated crucible 12 capable of containing a GaAs raw material melt therein.
Is to be solidified from the lower end to obtain a large-diameter GaAs single crystal.

More specifically, a crucible holder 14 is provided in an airtight container 10 of this apparatus made of quartz. The quartz crucible holder 14 has a so-called pBN
The crucible 12 made of (pyrotic BN) is accommodated. The lower end of the crucible 12 tapers downward so that a single crystal can easily grow in the crucible 12. The reason why the crucible 12 is pBN is that, in the case of a quartz crucible, there is a possibility that Si may be mixed into the GaAs raw material melt. A crucible shaft 18 is connected to a lower portion of the crucible holder 14 via a crucible driving mechanism 16, and can transmit rotation and vertical movement to the crucible 12. Around the crucible holder 14, heaters 20a-
20d can be arranged to heat the crucible 12. A plurality of thermocouples 22a are provided in the peripheral wall of the crucible holder 14.
To 22e, the crucible holder 14 and the GaAs
This makes it possible to measure the temperature distribution of the crucible that is in thermal equilibrium with the surface of the single crystal straight body.

In such an apparatus, the temperature distribution of the crucible 12 and the movement of the crucible holder 14 are controlled by the control device 30. The control device 30 mainly includes a CPU 32. The CPU 32 includes thermocouples 22a to 22a.
A temperature reading means 34 for reading a signal from e is connected via an input interface 36, and can transmit a reading signal to the CPU 32 of the control device 30.
Further, input means 38 such as a keyboard is connected to the CPU 32 via an input interface 36. When input of initial data (for example, the temperature of the high-temperature portion and the low-temperature portion, the temperature gradient, the cooling rate, and the like) on the temperature distribution and the like of the crucible 12 is performed from the input unit 38, the input unit 38 Can be transmitted to the CPU 32. Further, a storage means 42 is connected to the CPU 32 via an input / output interface 40. The storage unit 42 exchanges data with the CPU 32, thereby storing, for example, the thermocouples 22a to 22a.
The temperature distribution or the like of the crucible 12 is obtained based on the read signal from 2e, or the temperature distribution is compared with the initial data.

The CPU 32 has an output interface 44
Are connected to the heater controller 46 and the crucible drive mechanism controller 48 through the controller, and can transmit a control signal based on the initial data and the obtained temperature distribution to them. Then, the heaters 20a to 20a
20d and the crucible drive mechanism 16 are controlled, and the crucible 12
And the movement of the crucible holder 14 can be appropriately adjusted. When manufacturing the GaAs single crystal, display means 50 such as a display may be connected to the CPU 12 via the output interface 44 so that the temperature distribution of the crucible 12 can be observed in real time.

Next, the G of the present invention according to this device is
A method for producing an aAs single crystal will be described.

First, GaAs synthesized in advance is placed in a crucible.
After the s-polycrystal and B ₂ O ₃ are added as a starting material and a liquid sealing material, required initial data is input by input means. At this time, a temperature distribution having a low-temperature portion lower than the melting point of GaAs and a high-temperature portion higher than the melting point of GaAs through a temperature gradient is determined by the heaters 20a to 20d.
2 are formed on the lower side and the upper side, respectively.

Next, the crucible, which is moving the crucible holder 14 upward, is heated to 600 ° C. to melt B ₂ O ₃ . The melted B ₂ O ₃ serves as the liquid sealing material 52 to cover the GaAs polycrystal. Further, the crucible 12 is heated to a predetermined temperature to melt the GaAs polycrystal.

When the GaAs polycrystal is completely melted and the GaAs
After the raw material melt 54 has been formed, the crucible holder 14 is gradually moved downward as shown by the arrow in FIG. 1 and finally GaAs at the temperature of the low temperature portion (hereinafter, referred to as “solidification end temperature”).
The s raw material melt 54 is solidified, and a GaAs single crystal 56 is grown. The GaAs raw material melt 54 is completely solidified to form GaAs.
After the formation of the single crystal 56, the GaAs single crystal 56 is cooled. In the present embodiment, as the temperature of the GaAs single crystal decreases, the cooling rate of the GaAs single crystal is substantially increased.

Although the conventional cooling is performed at a substantially constant cooling rate as described above, the high-temperature Ga
Since each atom of the As single crystal is thermally excited and vibrates violently as compared with a low-temperature GaAs single crystal, slip which causes generation or growth of crystal defects such as dislocations is likely to occur due to slight stress. That is, the stress existing in the high-temperature GaAs single crystal tends to greatly affect the occurrence of slip. This tendency is due to the fact that the temperature distribution in the radial direction is easily formed during cooling, and large-diameter GaAs where large thermal stress is generated.
Appears remarkably in s single crystal. On the other hand, in a low-temperature GaAs single crystal, as compared with a high-temperature GaAs single crystal, slippage is less likely to occur due to the difference in thermal vibration of each atom, so that the influence of stress is reduced. Therefore, a temperature distribution having a larger temperature change in the radial direction than that of the high-temperature GaAs single crystal can be formed in the low-temperature GaAs single crystal. That is,
The cooling rate can be increased. Therefore, in the present embodiment, as the temperature of the GaAs single crystal decreases, the GaAs
The cooling rate of the s single crystal is substantially increased to balance thermal vibration and thermal stress. Further, by increasing the cooling rate, the cooling time can be shortened, so that the production throughput can be improved.

Next, the GaAs single crystal is formed into a columnar shape having an average diameter of the straight body of Dcm, and the cooling rate of the GaAs single crystal is set at a cooling rate dT on the surface of the straight body having a temperature of T ° C. / Dt (° C./hour) will be considered quantitatively, such as the cooling rate. Since the GaAs single crystal is cylindrical,
Since the temperature distribution in the radial direction of the GaAs single crystal during cooling can be considered to be axially symmetric, the temperature distribution may be approximated by a quadratic function. From the above assumption, GaAs
The stress distribution inside the single crystal can be calculated, and
From this stress distribution, the shear stress distribution in the sliding direction is obtained, and the maximum value σmax can be obtained. When the dislocation moves (when the dislocation density increases), the maximum value σmax
Exceeds the critical shear stress value σcrs at a certain temperature. Here, σcrs is a value known from various documents (for example, Bourret's critical shear stress value). From the above considerations, the average diameter of the straight body of the GaAs single crystal is Dcm
, The cooling rate dT / dt for cooling the surface temperature of the straight body from the temperature T ° C. to the room temperature is expressed by the following equation (1): dT / dt ≦ [820000 × exp ｛−0.0039 × (T + 273.1)
5) The present inventor has found that if Δ] / D ² , generation of crystal defects such as dislocations can be suppressed. The temperature gradient is 50
C / cm or less. If the temperature gradient is larger than 50 ° C./cm, not only crystal defects are likely to be introduced during the solidification of the GaAs raw material melt described later, but also amorphous GaAs tends to be formed. Such quantification enables precise control of the cooling rate and the like, so that a GaAs single crystal of uniform quality can be obtained.

In particular, the present inventors have revealed that when the temperature of a GaAs single crystal is 900 to 1000 ° C., the precipitation of As inside the crystal becomes remarkable. Therefore, in the present embodiment, in order to minimize the precipitation of As, the crystallization solidification temperature is set to at least 1000 ° C.
It is preferable that the lower limit of the cooling rate at 000 ° C. is 20 ° C./hour or more.

As described above, as a result of changing the cooling rate during the production of the GaAs single crystal in accordance with the temperature of the GaAs single crystal, the introduction of crystal defects and the precipitation of As are suppressed, and the quality of GaAs of a certain level or higher is suppressed. A single crystal can be obtained. This manufacturing method is extremely advantageous when manufacturing a large-diameter GaAs single crystal in which the temperature change in the radial direction is remarkable, leading to mass production of GaAs semiconductor devices and reduction in manufacturing cost.

Next, according to Examples and Comparative Examples,
Although the present invention will be described in detail, it goes without saying that the present invention is not limited thereto.

[0026]

EXAMPLE 1 A GaAs single crystal having an average diameter of a straight body of 152 mm (about 6 inches) was produced by the above-described vertical Bridgman method. First, 10 kg and 300 g of commercially available GaAs polycrystal having a purity of Six Nine and B ₂ O ₃ were prepared,
Put them in a crucible. Next, the temperature of the high temperature part and the solidification end temperature (that is, the temperature of the low temperature part) are each set to 1
245 ° C and 1100 ° C. Further, a temperature gradient of 5 ° C./cm was provided between the high temperature part and the low temperature part.

In such a state, the crucible is moved to the high-temperature portion side to convert the GaAs polycrystal into a GaAs raw material melt. G
After the aAs was completely melted, the crucible was moved to the low temperature part side to solidify the GaAs. After the GaAs was completely solidified at the solidification end temperature, the solidified GaAs was cooled according to a cooling rate dT / dt shown in Table 1 below. The cooling rate dT / dt satisfies the expression (1). The average dislocation density of the GaAs single crystal thus obtained was 3000 cm ^{-2 at the} straight body.
In addition, as a result of measuring the amount of As deposited on the surface of the mirror-polished wafer cut out of this single crystal, the scattering cross section was 0.0
Light scatterer concentrations greater than 6 μm ² were also 500 / wafer.

[0028]

[Table 1]

[0029] Comparative Example 1 except that the temperature gradient is different from example 1 in that a first embodiment of greater than 52 ° C. / cm is, Ga in the same manner as in Example 1
As single crystals were produced. The average dislocation density of the GaAs single crystal obtained at this time was 8000 cm ^-2 . Therefore, it was confirmed that the generation of crystal defects such as dislocations would not be suppressed unless the conditions of the temperature gradient of the present invention were satisfied.

Comparative Example 2 to Comparative Example 5 As shown in Table 1, a part of the cooling rate dT / dt from 1100 ° C. to room temperature exceeds the upper limit of the above-mentioned equation (1). A GaAs single crystal was manufactured in the same manner as in Example 1 except that Example 1 was different from Example 1. At this time, G
Only the average dislocation density of the aAs single crystal was larger than that of Example 1. Therefore, it was confirmed that the generation of crystal defects such as dislocations would not be suppressed unless the cooling rate condition of the present invention was satisfied.

REFERENCE EXAMPLE 1 Except that the solidification end temperature is 950 ° C. lower than that of Example 1, the solidification end temperature is the same as that of Example 1 except that Ga is
As single crystals were produced. The GaAs thus obtained
The average dislocation density and the light scattering substance concentration of the s single crystal were 4000
cm ^-2 and 3000-5000 / wafer. From this result, when the solidification end temperature is set to less than about 1000 ° C., A
It was confirmed that the precipitation of s was not suppressed.

Reference Example 2 A GaAs single crystal was produced by the same method as in Example 1 except that the cooling rate dT / dt at 1000 to 900 ° C. was 17 ° C./hour lower than that in Example 1. did. The average dislocation density and light scattering material concentration of the GaAs single crystal thus obtained were 3000 cm ^-2 and 5,000 to 5,000.
8000 / wafer. Therefore, 1000-9
It was confirmed that when the cooling rate dT / dt at 00 ° C was less than 20 ° C / hour, the precipitation of As was not suppressed.

Although the method for producing a GaAs single crystal of the present invention has been described according to the preferred embodiments and examples, the present invention is not limited to these. V as above
In addition to controlling the cooling rate and the like by the method B, for example, a gradient freeze (GF: Gradient Freeze) method and the like can form the above-described temperature gradient and measure the temperature. Can be. Therefore, a GaAs single crystal having the quality as described in the embodiment can be obtained.

[0034]

According to the method for manufacturing a GaAs single crystal of the present invention, after the GaAs single crystal is formed, the cooling rate of the GaAs single crystal is substantially increased within a predetermined range as the temperature of the GaAs single crystal decreases. As a result, it is possible to balance thermal stress and thermal vibration acting on the GaAs single crystal, and to suppress the occurrence of crystal defects and the like. Therefore,
A high quality GaAs single crystal can be obtained. Such a method is extremely advantageous when manufacturing large-diameter GaAs in which the temperature change in the radial direction is remarkable, and therefore leads to mass production of GaAs semiconductor devices and reduction in manufacturing cost.

In particular, in the cooling step of a GaAs single crystal solidified at a specific temperature, if the cooling rate at a specific temperature is set to a specific value or more, the precipitation of As can be suppressed, so that a GaAs single crystal having improved quality can be obtained. Crystals can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an apparatus useful for carrying out a method for producing a GaAs single crystal of the present invention.

[Explanation of symbols]

10 airtight container, 12 crucible, 14 crucible holder,
16: crucible drive mechanism, 18: crucible shaft, 20a-d ...
Heaters, 22a-e ... thermocouples, 30 ... control devices, 32 ...
CPU, 34: temperature reading means, 38: input means, 4
2 ... storage means, 46 ... heater controller, 48 ... crucible drive mechanism controller, 50 ... display means, 52 ... liquid sealing material, 54 ... GaAs raw material melt, 56 ... GaAs single crystal.

Claims (2)

[Claims] 1. A temperature gradient is formed between a high temperature part higher than the melting point of gallium arsenide and a low temperature part lower than the melting point of gallium arsenide, and a gallium arsenide raw material melt is relatively moved from the high temperature part to the low temperature part. By moving to and solidifying,
In the method for producing a gallium arsenide single crystal for forming a gallium arsenide single crystal, the cooling rate of the gallium arsenide single crystal is substantially increased as the temperature of the gallium arsenide single crystal decreases after the formation of the gallium arsenide single crystal. A cooling step, wherein the temperature gradient is set to 50 ° C./cm or less, and the cooling rate is set by the following formula (1): dT / dt ≦ [820000 × exp ｛−0.0039 × (T + 273.1)
5)｝] / D ² [where D represents the average diameter (cm) of the straight body portion when the gallium arsenide single crystal is formed into a columnar shape, and T represents the temperature (° C.) of the surface of the gallium arsenide single crystal. ) And dT / dt
Represents a cooling rate (° C./hour) when the temperature of the surface of the gallium arsenide single crystal is T in the cooling step]. Method. 2. The temperature of the low-temperature section is set to 1000 ° C. or higher, and the cooling rate in the cooling step is set to 900 ° C. ≦ T ≦ 100.
2. The method for producing a gallium arsenide single crystal according to claim 1, wherein the temperature is set to 20 ° C./hour or more at 0 ° C.