JP2009023870A - Method for manufacturing single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a single crystal deciding the optimum number of rotations of a crucible suitable for the diameter of the crucible. <P>SOLUTION: When a crucible 4 containing a raw material is rotated and heated from the outer periphery of the crucible 4 to melt the raw material and a single crystal 10 is grown at the lower part of a seed crystal 9 by bringing the seed crystal 9 into contact with the liquid surface of the raw material melt 3 at the center of the crucible 4 and then removing the seed crystal 9 away from the liquid surface, the number of rotations n (rpm) of the crucible 4 is controlled with respect to the radius r (m) of the crucible 4 to be n≥4.3e<SP>8.0r</SP>(wherein e is the base of natural logarithm). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a single crystal capable of determining an optimum number of crucible rotations suitable for the diameter of a crucible.

  In the single crystal manufacturing method such as GaAs single crystal manufacturing by the LEC method, while rotating the crucible containing the raw material, the crucible is heated from the outer peripheral side to melt the raw material, and the raw material melt is melted at the center of the crucible. After bringing the seed crystal into contact with the liquid surface, the seed crystal is separated from the liquid surface, whereby a single crystal is grown under the seed crystal.

JP-A-6-56582 JP 2004-10467 A JP 2004-10469 A JP-A-9-77590 JP 2002-20193 A JP-A-9-142997

  The prior art has a problem that the outer diameter of the crystal obtained by growth is unstable. If the crystal outer diameter deviates significantly from the predetermined value, a wafer of a predetermined size cannot be obtained from the crystal. In addition, polycrystallization occurs due to instability of the crystal outer diameter during crystal growth.

  Since the outer diameter of the crystal is unstable, the yield of obtaining a wafer from the crystal is about 75% in the prior art.

  The cause of the unstable crystal outer diameter is insufficient accuracy of outer diameter control, but there is a temperature gradient in the radial direction of the melt in the crucible. Since the crucible is rotated, the temperature distribution in the radial direction of the melt is a temperature distribution that rises from the center to the outer periphery of the crucible. This temperature rise is not uniform in the radial direction, the temperature gradient near the center is small, and the temperature gradient increases toward the outer periphery.

  When performing outer diameter control, it is important to manage the temperature gradient in the radial direction of the melt near the outer periphery. If the temperature gradient is small in the vicinity of the outer periphery, it is easily affected by disturbance factors, and the crystal outer diameter becomes unstable.

  By the way, the temperature gradient in the radial direction of the melt in the crucible tends to depend on the diameter of the crucible. Assuming that the number of revolutions of the crucible is constant, the knowledge that the temperature gradient in the radial direction of the melt is smaller as the diameter of the crucible is larger is obtained. On the other hand, it has been found that increasing the number of revolutions of the crucible can increase the temperature gradient in the radial direction of the melt.

  However, there are many unclear points about the optimum rotational speed of the crucible that matches the diameter of the crucible, and a technique for determining the optimal rotational speed has not been established.

  Accordingly, an object of the present invention is to provide a method for producing a single crystal that solves the above-described problems and can determine the optimum number of rotations of the crucible in accordance with the diameter of the crucible.

In order to achieve the above object, the present invention is to heat the crucible from the outer peripheral side while rotating the crucible containing the raw material, to melt the raw material, and to seed the liquid surface of the raw material melt at the center of the crucible. After contacting the crystal, when the single crystal is grown under the seed crystal by separating the seed crystal from the liquid surface, the crucible rotation speed n (rpm) is set to the radius r ( m) for n ≧ 4.3e ^8.0r (e is the base of natural logarithm)
It is what.

  Gallium arsenide single crystal may be grown using gallium and arsenic as the raw material.

  The present invention exhibits the following excellent effects.

  (1) The optimum number of crucible rotations suitable for the diameter of the crucible can be determined.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows an LEC GaAs single crystal manufacturing apparatus as an embodiment of the single crystal manufacturing method of the present invention. As shown in the figure, an LEC GaAs single crystal manufacturing apparatus 1 includes a chamber 2 as a furnace body, a PBN crucible (hereinafter simply referred to as a container for containing Ga and As as raw materials, and a GaAs melt 3 as a melt thereof. 4), a crucible shaft 5 that supports and rotates the crucible 4, and a side carbon heater 6 and a lower carbon heater 7 disposed around the crucible 4 in order to heat the crucible 4 from the outer peripheral side and the bottom side. In addition to the raw material, it is put into the crucible 4, boron trioxide 8 which is an As volatilization preventive agent, and the central part of the crucible 4 from above, while holding the seed crystal 9 which is the base of the crystal, and opposite to the crucible 4 The pulling shaft 11 that pulls up the GaAs single crystal 10 that is a crystal grown from the seed crystal 9, and the weight of the GaAs single crystal 10 is attached to the pulling shaft 11. And a load cell 12 to a constant.

  A method of manufacturing the GaAs single crystal 10 using the LEC GaAs single crystal manufacturing apparatus 1 shown in FIG. 1 will be described. First, Ga, As, and boron trioxide 8 are charged into the crucible 4, and the crucible 4 is supported by the crucible shaft 5 in the chamber 2. The seed crystal 9 is held at the lower end of the pulling shaft 11. The seed crystal 9 generally has a (100) plane that is in contact with the GaAs melt 3.

  Thereafter, the chamber 2 is evacuated and then filled with an inert gas. By energizing the side carbon heater 6 and the lower carbon heater 7 to raise the temperature in the chamber 2, Ga and As are synthesized to produce GaAs. Thereafter, GaAs is melted by further raising the temperature.

  Next, the pull-up shaft 11 and the crucible shaft 5 are rotated so that the rotation directions of the pull-up shaft 11 and the crucible shaft 5 are reversed. Here, when the crucible 4 is rotated by the crucible shaft 5, the temperature distribution in the radial direction of the GaAs melt 3 in the crucible 4 becomes a temperature distribution in which the temperature gradually increases from the center to the outer periphery of the crucible 4. .

  In this state, the pulling shaft 11 is lowered to bring the seed crystal 9 into contact with the GaAs melt 3. Next, while gradually lowering the set temperature of the side carbon heater 6 and the lower carbon heater 7, the pulling shaft 11 is raised at a constant speed, and the seed crystal 9 is separated from the liquid surface. A crystal shoulder is formed while gradually increasing the crystal diameter. When the target crystal outer diameter is reached, the GaAs single crystal 10 is grown by continuing to raise the pull-up shaft 11 while controlling the outer diameter in order to keep the outer diameter constant.

  In the conventional outer diameter control, the outer diameter of the GaAs single crystal 10 is calculated from the increase per unit time of the weight of the GaAs single crystal 10 measured by the load cell 12 and the rising distance per unit time of the pulling shaft 11. Is calculated. The outer diameter control is performed by feeding back the difference between the calculated outer diameter and the target outer diameter to the set temperature of the side carbon heater 6 and the lower carbon heater 7.

  At this time, in order to stabilize the crystal outer diameter, it is important to optimize the temperature gradient in the radial direction of the melt. Although it has been known that the temperature gradient is related to the crucible diameter and the crucible rotation speed, as described above, the optimum crucible rotation speed suitable for the crucible diameter is unknown. However, a technique for determining the optimum rotational speed has not been established.

Therefore, the present inventor conducted an experiment to investigate the number of rotations of the crucible where the outer diameter of the crystal is stabilized, using crucibles of various diameters in order to clarify this. As a result, the relationship between the crucible rotation speed n (rpm) and the crucible radius r (m) is
n ≧ 4.3e ^8.0r (e is the base of natural logarithm)
It was found that the outer diameter of the crystal is stable when satisfying

  Hereinafter, the progress and results of the above-described experiment will be described using the example of the present invention.

  Using the LEC method GaAs single crystal manufacturing apparatus 1 shown in FIG. 1, a GaAs single crystal 10 having a size of φ0.15 m was manufactured under various conditions.

  The procedure of the trial production is the same under all conditions. First, Ga, As, and boron trioxide 8 are introduced into the crucible 4 and the crucible 4 is set in the chamber 2. A seed crystal 9 is attached to the lower end of the pull-up shaft 11, and the surface of the seed crystal 9 in contact with the GaAs melt 3 is defined as a (100) plane. Thereafter, the inside of the chamber 2 is evacuated, filled with an inert gas, the side carbon heater 6 and the lower carbon heater 7 are energized to raise the temperature in the chamber 2, and GaAs is produced by synthesizing Ga and As. Then, the temperature is further raised to melt GaAs.

  Next, the pull-up shaft 11 and the crucible shaft 5 are rotated in opposite directions. In this state, the pull-up shaft 11 is lowered to bring the seed crystal 9 into contact with the GaAs melt 3, and then the pull-up shaft 11 is moved while gradually lowering the set temperatures of the side carbon heater 6 and the lower carbon heater 7. The GaAs single crystal 10 is grown at a rate of 10 mm / h.

There are three types of conditions for the radius of the crucible 4: 4, 7, 9 (× 2.54 × 10 ⁻² ) m. The set weight of Ga, As, and boron trioxide 8 at that time is such that the thickness (from the liquid surface to the bottom) of the GaAs melt 3 after the synthesis of Ga and As is 100 mm, and the thickness of boron trioxide 8 is 15 mm. Adjust as follows.

  With respect to the three types of crucibles 4, as a condition for the rotational speed of the crucible 4, the trial production was repeated by increasing the rotational speed from 0 rpm by 1 rpm.

  For the GaAs single crystal 10 prototyped under each condition as described above, the number of wafers acquired was investigated and the yield was determined. The result is shown in FIG. As shown in the figure, it was found that, in all three types of crucibles 4, increasing the number of rotations of the crucible 4 improves the wafer acquisition yield. Furthermore, for each type of crucible 4, it was found that the wafer acquisition yield was stabilized at about 85% when a certain number of rotations was exceeded.

In response to this result, several types of crucibles 4 with a radius of 4 to 9 (× 2.54 × 10 ⁻² ) m were manufactured, and the same trial production was performed. The wafer acquisition yield exceeded about 85%. The number of rotations of the crucible 4 at that time was investigated. The result is shown in FIG. As shown in the figure, the number of rotations of the crucible 4 when the wafer acquisition yield exceeds about 85% is related to the diameter of the crucible 4.

When the approximate curve was calculated from the data of FIG.
n = 4.3e ^8.0r
It became. From this,
n ≧ 4.3e ^8.0r
When the above relationship is satisfied, it can be concluded that wafer acquisition is possible with a stable yield. This factor seems to be due to the stabilization of the crystal outer diameter when the crystal is grown under the condition where the above relationship is satisfied.

  In the above embodiment, the LEC GaAs single crystal is manufactured. However, the present invention can also be applied to the LEC single crystal manufacturing using other raw materials and the CZ method.

  The present invention can improve profitability by improving the wafer acquisition yield by stabilizing the crystal outer diameter.

It is a block diagram of the LEC method GaAs single-crystal manufacturing apparatus which shows one Embodiment of this invention. It is a crucible rotation speed vs. wafer acquisition yield characteristic graph using a crucible diameter as a parameter. It is a graph showing the crucible rotation speed at which the wafer acquisition yield is about 85% or more with respect to the crucible diameter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 LEC method GaAs single crystal manufacturing apparatus 2 Chamber 3 GaAs melt 4 Crucible 5 Crucible shaft 6 Side carbon heater 7 Lower carbon heater 8 Boron trioxide 9 Seed crystal 10 GaAs single crystal 11 Pull up shaft 12 Load cell

Claims (2)

While rotating the crucible containing the raw material, the crucible is heated from the outer peripheral side to melt the raw material, and the seed crystal is brought into contact with the liquid surface of the raw material melt at the center of the crucible. When the single crystal is grown under the seed crystal by being separated from the liquid surface, the crucible rotation speed n (rpm) is set to the crucible radius r (m).
n ≧ 4.3e ^8.0r (e is the base of natural logarithm)
A method for producing a single crystal, comprising:   2. The method for producing a single crystal according to claim 1, wherein gallium and arsenic are used as the raw material to grow a gallium arsenide single crystal.

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