JPH0699232B2 - Compound semiconductor single crystal manufacturing equipment - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an apparatus for producing a compound semiconductor single crystal having a high decomposition pressure at the melting point of GaAs or the like by the direct synthesis LEC method, and in particular, aims to automate the direct synthesis process. Related equipment.

[Technical background of the invention and its problems]

The direct synthesis LEC method is used as a method for producing a compound semiconductor single crystal having a high decomposition pressure at the melting point of GaAs or the like. This method is characterized in that a high-purity single crystal can be obtained and the raw material cost is low, and is widely used especially for the production of a GaAs single crystal, which has recently attracted attention as a substrate for ultra-high-speed ICs.

A conventional apparatus for producing a compound semiconductor single crystal using the direct synthesis LEC method will be described with reference to FIG. A crucible 2 is provided in the high-pressure vessel 1, and metal crucible, which is a raw material, is placed in the crucible 2.
3 and metal As 4 and B ₂ O ₃ which is a sealant are charged. After pressurizing the inside of the container 1 with an inert gas, the crucible 2 is heated by a heating element 6 that coaxially surrounds the crucible 2 to form a raw material melt and a liquid capsule layer covering the melt. The decomposition of the raw material melt at high temperature is suppressed by the liquid capsule layer and the pressurized inert gas. A single crystal is produced by bringing a seed crystal (not shown) into contact with the raw material melt through a liquid capsule and then pulling by rotation. This raw material synthesis process is roughly classified into (1) a step of melting the sealant and coating the raw material,
It consists of three steps: (2) reacting the Ga3 and As4 materials to synthesize a GaAs polycrystal, and (3) melting the synthesized GaAs. These steps are performed by adjusting the heating power of the heating element 6 while monitoring the output of the thermocouple 7 attached to the bottom of the crucible. Therefore, the heating power control unit 9 is independently provided with power control means such as a power detector 8, a power controller 41, a temperature controller 42, a manual power setting device 43, a changeover switch 44, and an SCR 45. Conventionally, the above operation was manually performed so that a predetermined heating pattern can be obtained empirically depending on the skill of the operator. For example, in the step (1), the power regulator 41 or the manual power setting device
By 43, heating power is slowly added in steps until it approaches the power at which the sealant melts. Similarly, in the step (2), the heating power is rapidly increased stepwise near the power at which GaAs melts. In the step (3), the temperature is changed to the temperature controller 42 by the changeover switch 44, and the temperature is slowly raised to the temperature at which GaAs melts.

However, since this conventional method relies on the experience of the operator, it has drawbacks such as poor reproducibility, increased fatigue of the operator, increased work time, and erroneous operation. In particular, if the amount of As scattered at the time of direct synthesis cannot be kept constant, it becomes difficult to control the composition of Ga / As in the obtained melt, and as a result, there arises a problem that the crystal characteristics deviate or vary. Further, the larger the size of the furnace, the longer the thermal time constant of the furnace, and therefore the time required for step (1) becomes longer. Even if the same furnace is used and the furnace conditions are changed, an appropriate heating pattern and heating power required therefor are set. However, there are drawbacks such as requiring 2-3 experiments.

On the other hand, if the step (1) is performed from the power control to the temperature control, the time can be shortened. However, the normal temperature controller 42 must set the control constants so that the control is optimal at the temperature when pulling the crystal (up to 1250 ° C), and the temperature at which the sealant melts (up to 600 ° C). In the following, the constants are inappropriate. As a result, hunting, overshoot, etc. occur and the temperature control accuracy is poor, and conversely, there is a drawback that reproducibility is reduced. Therefore, in step (1) and step (3), the constant is changed each time, or the temperature regulator 42 is individually set to two.
It is necessary to prepare a table, etc., and there is a problem that the operation and the apparatus are complicated and expensive.

Therefore, the conventional apparatus has a drawback that not only the direct synthesis process can be automated, but also the crystal production process from the start of heating to the crystal extraction cannot be fully automated.

[Object of the Invention]

In view of the above points, the present invention, in particular, the production of a single crystal capable of pulling a polycrystal of stable quality by automatically controlling the direct synthesis process to keep the amount of scattered raw materials constant and controlling the melt composition. The purpose is to provide a device.

[Outline of Invention]

The outline of the present invention will be described with reference to FIGS. 1 and 2. The body of the pulling furnace is well known, and the heating controller 9 is attached to it. This basic configuration is the same as that of the conventional FIG. As shown in FIG. 2, the heating control unit 9 stores heating patterns and control constant setting means 10 to 12 corresponding to each step, that is, melting of the sealant, synthesis of the polycrystal, and melting step of the polycrystal. Further, there is provided a switching means 14 for sequentially selecting these by the selection means 13 and supplying them to the electric power control means 15 or the temperature control means 16 so as to match the heating pattern. Then, the outputs of the thermocouple 7 and the power detector 8 are processed by the selecting means 13 and the switching means 14 in accordance with each step, and a control signal is supplied to the power setting means 17.

The control of the direct synthesis process is performed as follows. That is, in step I shown in FIG. 2, the encapsulant is heated slowly and kept at a sufficient temperature until it is completely melted near the softening point. This heating pattern is set appropriately from the sublimation rate of As and the softening rate of the sealant. The heating temperature control constant is set to an appropriate value so that hunting during temperature rise and overshoot during switching from temperature rise to temperature hold do not occur. This can be determined by the Ziegler-Nichols method or the like from the thermal characteristics of the furnace in step I. The end of step I is judged from the holding temperature and holding time, and the process proceeds to step II. In step II, As is melted and Ga
Is reacted with to synthesize a polycrystal of GaAs. This synthesis reaction is an exothermic reaction, and the heating pattern is to rapidly heat the As to suppress the scattering of As and complete the reaction at once. Therefore, heating is performed by electric power control, and after the temperature reaches a steady state, step II is terminated and the process proceeds to step III. In step III, the synthesized polycrystal is slowly heated and melted. Here, heating is performed again by temperature control, but since the furnace pressure and temperature are considerably different from those in step I, the control constant is also set to an appropriate value corresponding thereto.

〔The invention's effect〕

 According to the present invention, the following effects can be obtained.

(1) The synthesis can be automatically performed directly without relying on the conventional manual operation by the skilled worker.

(2) The amount of As scattered can be constantly suppressed, and a melt having a predetermined composition can be obtained with good reproducibility.

(3) Since a single crystal with stable characteristics can be obtained and the reproducibility is good, the loss of the crystal raw material is reduced by about 10% as compared with the conventional one, and the crystal production yield is improved.

(4) The direct synthesis can be fully automated by incorporating the function of controlling the gas pressure in the furnace during the direct synthesis.

(5) Single crystal production can be automated by combining with a diameter control device.

(6) Productivity is improved by applying it industrially.

Example of Invention

FIG. 3 is a diagram showing a device configuration of an embodiment of the present invention in which a microcomputer is used as a control unit. In the figure, 1
Is a high pressure vessel, 2 is a crucible, 3 is Ca, 4 is As, 5 is B ₂ O ₃ ,
Reference numeral 6 is a heating element, 7 is a thermocouple, and 31 is an SCR device for supplying electric power to the heating element 6. The above-mentioned crystal pulling apparatus main body and its auxiliary equipment are conventionally known.

The outputs of the thermocouple 7 and the power detector 8 are selected by the scanner 21, converted into a digital signal by the A / D converter 22, and latched in the input port 23. The data of the input port 23 is taken into the microcomputer 24 controlled by the timer 28. The timer 28 is provided to operate the microcomputer 24 at a constant cycle. The microcomputer 24 is basically a CPU 25,
It is composed of RAM 26 and ROM 27. At the cycle set by the timer 28, the CPU 25 collects temperature and power data from the input port 23 according to the program of the ROM 27, performs arithmetic processing while exchanging data with the RAM 26, and sets control signal data for heating power. Is output to the output port 29. The data of the output port 29 is converted to an analog signal by the D / A converter 30 and then SCR
Given to device 31.

The control flow by the microcomputer is shown in FIG. 4, and the operation of the direct synthesis control will be described with reference to this and FIG. When the program starts, first step P1
In step P2, the FLAG determination is made, and since F = 1, the process branches to step P3. In step P3, the sealing agent melting heating pattern and the temperature control constant are initialized. Next, the temperature control loop consisting of steps P4 to P5 is executed at regular intervals, and is repeated until it is determined that the sealant has melted. That is, in step P4, the temperature target value is calculated as a function of time according to the set pattern. In step P5, the measured value of the crucible bottom temperature is captured. In step P6, the difference between the target temperature value and the measured value is detected, and the correction amount of the heating power is calculated and output so that the difference becomes zero. The correction amount can be calculated by a known PID control formula, but in this case, it is desirable to use the velocity type PID control formula. In step P7, melting of the sealant is determined. And if it is determined that it has melted, step
The process proceeds to P8, the mode is updated to F = 2, and the process returns to step P2.

In the next cycle, step P2 is F = 2, so step P9
And the polycrystal synthesis heating pattern and power control constants are reinitialized. Next, the power control loop including steps P10 to P13 is executed at a constant cycle and is repeated until the synthesis is completed. In step P10, the power target value is calculated as a function of time according to the set pattern. Step P1
At 1, the difference between the target value and the measured value of the electric power is detected, and the heating electric power is set so that the difference becomes zero. After it is determined in step P13 that the synthesis is completed, the process proceeds to step P14, the mode is updated to F = 3, and the process returns to step P2.

Since F = 3 in step P2, the process goes to step P15, and the polycrystalline melting heating pattern and the control constant are initialized again. Next, a temperature control loop consisting of steps P16 to P19 is executed in a constant cycle and repeated until the synthetic polycrystal melts. The operations of steps P16 to P19 are the same as steps P4 to P7, and thus the description thereof is omitted. When it is determined in step P19 that the polycrystal has melted, a series of operations ends, and the direct synthesis is completed.

Next, more specifically, the case of pulling up a GaAs single crystal by direct synthesis will be described. A total of 3 kg of Ga and As used as raw materials in a PBN crucible with a diameter of 150 mm (charge composition ratio Ga / As = 0.9
5) and 600 g of B ₂ O ₃ as a sealant are placed in the furnace and A
After pressurizing to ~ 35 atm with r gas, the program was run and heating was started according to the steps shown in FIG. In Step I, the melting temperature of B ₂ O ₃ could be judged by slowly raising the temperature to near the softening point of B ₂ O ₃ (about 13 mV by the electromotive force of the thermocouple) in about 90 minutes and holding it for about 30 minutes. Next, proceed to process II, where 2 at approximately 1.5 kW / min
Polycrystalline synthesis was determined by increasing the power to 5 kW. At this time, the pressure in the furnace had risen to about 70 atm.
Further, in Step III, the melting of the GaAs polycrystal was judged by raising the temperature to about 26.5 mV in about 30 minutes, and a series of control operations was completed. After that, seeding was performed by setting the pressure to 20 atm, and about 2.7 kg of <100> GaAs single crystal was manufactured. The amount of As scattered at the time of synthesis after completion of pulling was calculated to be -40 g. When the specific resistance of the obtained single crystal was measured, it was 5 × 10 ⁷ Ω · cm or more from the head to the tail, and heat treatment (850 ° C., 15 minutes, As pressure)
Even after 4 Torr), it was a stable single crystal with a quality of 2 × 10 ⁷ Ω · cm or more without thermal denaturation.

Next, after changing the feed composition ratio (Ga / As) of the raw material from 0.89 to 1.03 and pulling up the single crystal by direct synthesis, the initial composition ratio of the melt was estimated from the amount of As scattered during synthesis and When the relationship was determined, the results shown in FIG. 5 were obtained. From this, it was found that the composition ratio of the charged material and the composition ratio of the initial melt have a substantially linear relationship and have reproducibility.

As described above, according to the present embodiment, not only automatic direct synthesis can be performed without relying on the skill of the operator, but also control of the initial melt composition ratio, which is difficult manually, can be easily performed with good reproducibility. High quality crystals with stable electrical characteristics can be obtained with good yield.

In the present invention, the control unit may be configured by an individual circuit,
The use of a microcomputer allows higher precision and easier implementation.

Further, the present invention is applicable to other III-V group single crystals such as InP and GaP and Z.
It is also applicable to the case where a II-IV group single crystal such as nS or ZzSe is produced by a direct synthesis method.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of the present invention, FIG. 2 is a diagram showing an example of a direct synthesis process, FIG. 3 is a diagram showing a configuration of an embodiment of the present invention, and FIG. FIG. 5 is a flow chart for explaining the control operation, FIG. 5 is a diagram showing an example of the effect of the present invention, and FIG. 6 is a diagram showing the configuration of a conventional device. DESCRIPTION OF SYMBOLS 1 ... High-pressure container, 2 ... Crucible, 3 ... Ga, 4 ... As, 5 ... Sealing agent, 6 ... Heating element, 7 ... Thermocouple, 8 ... Power detector, 9 ... Heating power control section, 10 ... Sealing Agent melting pattern and control constant setting means, 11 ... Polycrystal synthesis pattern and control constant setting means, 12 ... Polycrystal melting pattern and control constant setting means, 13
... selecting means, 14 ... switching means, 15 ... power control means, 16 ... temperature control means, 17 ... power setting means, 21 ... scanner, 22 ... A /
D converter, 23 ... Input port, 24 ... Microcomputer, 25 ... CPU, 26 ... RAM, 27 ... ROM, 28 ... Timer, 29 ... Output port, 30 ... D / A converter, 31
… SCR device.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazutaka Terashima 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research Institute, Inc. (72) Inventor Masayuki Watanabe Komukai-Toshiba, Kawasaki-shi, Kanagawa Town No. 1 Incorporated Toshiba Research Institute (72) Inventor Tetsuro Saito No. 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa (56) Incorporated company Toshiba Tamagawa Plant (JP) 60-27694 A) JP 56-125296 (JP, A) JP 60-264390 (JP, A) JP 59-57986 (JP, A) Actual development JP 56-98869 (JP, U) JP 51 -5993 (JP, B2) JP-B-52-30154 (JP, B2)

Claims (1)

[Claims] 1. An apparatus for pulling a compound semiconductor single crystal by a direct synthesis LEC method, comprising: (a) means for detecting the temperature of the bottom of a crucible containing a raw material and a sealant; and (b) a heating element. Means for detecting the electric power supplied, (c) Means for setting the electric power supplied to the heating element, (d) Means for controlling the temperature of the bottom of the crucible, (e) Controlling the electric power supplied to the heating element Means, (f) means for setting a sealant melting heating pattern for melting the sealant and a heating temperature control constant, (g) a polycrystal synthesis heating pattern for melting the raw material and synthesizing a polycrystal Means for setting a heating power control constant, (h) means for setting a polycrystal melting heating pattern for melting a synthesized polycrystal and a heating temperature control constant, and (i) heating patterns of (f) to (h) above And control constants are sequentially selected to set the heating pattern. An apparatus for producing a compound semiconductor single crystal, comprising: switching means for supplying the electric power control means or the temperature control means so as to coincide with each other.