JPH09165293A - Growing method for single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for growing a single crystal in a high yield by growing the single crystal having its diameter controlled at a constant value despite of having a long length. SOLUTION: This method for growing a single crystal is to set at least one of a time constant and a gain of the responding function of the diameter of the single crystal 21 to the temperature of a heater 13 reducing monotonously with the lapse of the growing time for the straight drum part of the single crystal 21. Since, even if the remaining amount of the molten liquid 14 is reduced or the relative position of the heater 13 with the molten liquid 14 is changed, the responding property of the diameter of the single crystal 21 to the temperature of the heater 13 does not become faster, it is possible to grow the single crystal 21 having its diameter controlled at a constant value despite of having a long length.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a single crystal by a pulling method using model predictive control.

[0002]

2. Description of the Related Art When a single crystal is grown by a pulling method, if the diameter of the single crystal cannot be controlled to a constant value, it is necessary to grow a single crystal with a larger diameter in consideration of the fluctuation range of the diameter. In addition, since the heat radiation from the single crystal becomes unstable and the proportion of the polycrystals that cannot be used as a product increases, the single crystal cannot be grown with a high yield.

Therefore, the response function of the diameter of the single crystal with respect to the temperature at which the raw material is heated to form the melt of the raw material is obtained in advance, and is obtained by the heating history during the actual growth of the single crystal and the weight method. A model in which the predicted value of the diameter of the single crystal after a lapse of a predetermined time from the diameter of the single crystal is obtained from the response function, and the heating temperature is controlled so that the predicted value matches the target value after the lapse of the predetermined time. A method using predictive control is known (for example, Japanese Patent Laid-Open No. 4-108687).

[0004]

However, in the actual growth of the single crystal, even if the model predictive control as described above is used, the predicted value obtained by the response function and The difference from the diameter of the grown single crystal was large.
Therefore, even if the heating temperature is controlled so that the predicted value and the target value match, the diameter of the actually grown single crystal deviates from the target value, and it is still difficult to grow the single crystal with a high yield. there were.

According to the inventor of the present application, such a difference between the predicted value and the target value is caused by a change in the growth environment due to the growth of the single crystal, such as a decrease in the remaining amount of the melt or a heating due to this decrease. It is considered that this is due to the change in the relative position between the means and the melt. This may be because the deviation between the predicted value and the target value becomes more remarkable when a large amount of melt is used to grow a long single crystal.

Therefore, an object of the present invention is to provide a method capable of growing a single crystal whose diameter is controlled to be a constant value even if it is long and growing the single crystal with a high yield. There is.

[0007]

A method for growing a single crystal according to claim 1 is to grow a single crystal by bringing a seed crystal into contact with a melt formed by heating a raw material and pulling the seed crystal from the melt. When growing, a response function of the diameter of the single crystal with respect to the heating temperature is obtained in advance, and the predicted value of the diameter after a lapse of a predetermined time from the heating history and the diameter during the growth is the response function. Obtained from, in the single crystal growth method of controlling the temperature of the heating so that this predicted value matches the target value of the diameter after the predetermined time has elapsed, the growth time of the straight body part of the single crystal elapses. It is characterized in that at least one of the time constant and the gain of the response function is monotonically decreased in accordance with.

The method for growing a single crystal according to claim 2 is the method according to claim 1.
In the method for growing a single crystal as described above, at least one of the time constant and the gain monotonically decreases as the remaining amount of the melt decreases.

The method for growing a single crystal according to claim 3 is the method according to claim 1.
In the method for growing a single crystal, the at least one of the time constant and the gain monotonically decreases as the relative position between the heating means and the melt changes.

The method for growing a single crystal according to claim 4 is the method according to claim 1.
1 to 3, at least one of the time constant and the gain is reduced in a linear function.

In the method for growing a single crystal according to the present invention, at least one of the time constant and the gain of the response function of the diameter of the single crystal with respect to the heating temperature is monotonic as the growing time of the straight body portion of the single crystal elapses. As the melt remains small, the responsiveness of the diameter of the single crystal to the heating temperature becomes faster even if the remaining amount of the melt decreases or the relative position between the heating means and the melt changes. There is no.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a target radius is 55 mm and a length is 200 mm so that a wafer having a diameter of 4 inches can be obtained.
A specific example of the present invention applied when a GaAs single crystal having a size of mm is grown by a liquid sealing pulling method which is a kind of pulling method will be described with reference to FIGS.

In this specific example, as shown in FIG.
PBN located in 1 and having a diameter of 300 mm
In a crucible 12 made of (pyrolytic boron nitride), 15 kg of high-purity GaAs used as a raw material and 2.5 k of B ₂ O _{3 used as a} sealant.
g, and the air in the growth furnace 11 is exhausted by a vacuum pump, and then the pressure in the growth furnace 11 is adjusted to 20 atm with Ar gas.

Then, power is supplied to the heater 13 to heat the crucible 12 to melt GaAs and B ₂ O ₃ in the crucible 12 to form a GaAs melt 14 and melt B ₂ O _3. A melt of B ₂ O ₃ (not shown) is formed on the melt 14 of GaAs, and the melt of GaAs 14 is sealed in the crucible 12 with the melt of B ₂ O ₃ .

After that, while controlling the electric power supplied to the heater 13 so that the growth furnace 11 has a temperature distribution in which the solid-liquid interface shape between the growing crystal and the melt 14 becomes convex downward, The seed crystal 15 is brought into contact with the melt 14, the crystal pulling shaft 16 suspending the seed crystal 15 is rotated clockwise at 6 revolutions / minute, and the crucible shaft 17 supporting the crucible 12 is rotated. The crystal orientation is <100> by pulling the seed crystal 15 upward at a speed of 6 to 10 mm / hour while rotating the steel in the counterclockwise direction at 20 to 30 rotations / minute.
A single crystal 21 of GaAs is obtained.

Until the single crystal 21 reaches the target radius, that is, while the shoulder portion of the single crystal 21 is grown, the single crystal 21
The temperature of the heater 13 is manually controlled according to the actual shape of the single crystal 21, and after the single crystal 21 reaches the target radius, that is, after the straight body portion of the single crystal 21 is grown, the single crystal 21 remains at the target radius. In order to grow the seeds, the temperature of the heater 13 was automatically controlled as follows.

That is, first, as shown in FIG. 2 (a), by heating the heater 13 at a temperature set in steps,
It is assumed that the radius of the single crystal 21 responds stepwise as shown in FIG. Then, the radius y _{M at} time t + j
(T + j) was modeled as a variation from the radius y _M (t) at time t, and the response function of the following equation was adopted.

[0018]

[Equation 1]

The second term in this equation is the contribution due to future heating, and the third term is the contribution due to past heating, that is, the heating history. In this specific example, M = 3, s
= 100, j = 10 to 14, but since the sampling interval, that is, the time for one section is set to 2 minutes, M = 6 minutes,
It becomes s = 200 minutes and j = 20 to 28 minutes.

On the other hand, the weight increase amount dW of the single crystal 21 per unit time obtained by the weight measuring device 22 and the growth length L of the single crystal 21 per unit time obtained from the pulling rate by the crystal pulling shaft 16. And the density ρ of the single crystal 21,
The arithmetic circuit 23 calculates the radius r of the single crystal 21 by the following conversion formula. dW = πr ² Lρ

Since the radius r of the single crystal 21 thus obtained corresponds to y _M (t) in the above-mentioned response function, the arithmetic circuit 23 uses this response function to calculate t + 10.
Predicted values at t + 14 y _M (t + 10) to y _M (t
+14), and these predicted values and t + 10 to t + 14
Heater 1 that minimizes the sum of squares of the difference from the target value at
The temperatures Δu (t + 0) to Δu (t + 2) of 3 are obtained.

The heater control device 24 is connected to the arithmetic circuit 2
3 to the temperature of the heater 13 Δu (t + 0) to Δu (t +
2) and input the temperature of the heater 13 to these temperatures Δu
Control from (t + 0) to Δu (t + 2). Such control of the temperature of the heater 13 is performed every section, that is, every two minutes.

By the way, in this example, as is clear from the expression of the time constant T in the above-mentioned response function, this time constant T decreases linearly as the remaining amount of the melt 14 decreases. ing. Therefore, as the remaining amount of the melt 14 decreases, the melt 1
Despite the decrease in the heat capacity of No. 4, the responsiveness of the diameter of the single crystal 21 to the temperature of the heater 13 does not increase.
As a result, as shown in FIG. 3, a GaAs single crystal 21 having a radius deviation of 4 mm or less and a length of 250 mm could be grown.

On the other hand, even if the response function of the above-mentioned form is used, if the time constant T therein is a constant value of, for example, 15 as in the conventional example, as shown in FIG. It was possible to grow only a single crystal with a large variation.

In the above specific example, the coefficient for the remaining amount of melt in the time constant T is set to 1. However, if this coefficient is large and the degree of decrease of the time constant T is large, the heater 1
The control of the diameter of the single crystal 21 is delayed with respect to the control of the temperature of 3,
On the contrary, if this coefficient is small and the degree of decrease of the time constant T is small, the control of the diameter of the single crystal 21 is too fast with respect to the control of the temperature of the heater 13, and in any case, fluctuations from the target diameter will occur. Grows larger.

Note that this coefficient is determined by the arrangement of the heater 13, the size of the heater 13, the size of the growing furnace 11, etc.
It is a value depending on the characteristics of 1 and the single crystal 21 to be grown.

Further, in the above-mentioned specific example, the automatic control of the temperature of the heater 13 is started from the time when the straight body portion of the single crystal 21 is grown, but the straight body portion is heated to 100 after the straight body portion is grown.
You may start the automatic control of the temperature of the heater 13 until it grows up to about mm.

Further, in the above-mentioned specific example, as is clear from the expression of the time constant T in the response function, only the remaining amount of the melt 14 is taken into consideration in determining the time constant T, but the single crystal Considering the change in the relative position between the heater 13 and the melt 14 due to the growth of 21, the controllability of the diameter of the single crystal 21 is expected to be further improved.

Further, in the above-described specific example, the time constant T in the response function is made small as a linear function, but it is sufficient that the time constant T is made monotonically small, and it becomes not necessarily a linear function. You don't have to be. Further, in the above specific example,
Although the time constant T in the response function is made smaller with the growth of the single crystal 21, the gain K in the response function may be made smaller, or both the time constant T and the gain K may be made smaller. .

Further, although the present invention is applied to the growth of a GaAs single crystal by the liquid sealing pulling method in the above-mentioned specific example, the present invention is also applied to the growth of an element single crystal which is not sealed by a liquid. Of course it can be applied.

[0031]

In the method for growing a single crystal according to the present invention, even if the remaining amount of the melt is reduced or the relative position between the heating means and the melt is changed, the single crystal can be grown with respect to the heating temperature. Since the responsiveness of the diameter does not increase, it is possible to grow a single crystal in which the diameter is controlled to a constant value even with a long length, and the single crystal can be grown with a high yield.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus for practicing one embodiment of the present invention.

FIG. 2 is a graph showing a response function used in a specific example.

FIG. 3 is a side view of a single crystal grown in a specific example.

FIG. 4 is a side view of a single crystal grown in a conventional example of the present invention.

[Explanation of symbols]

 13 heater 14 melt 15 seed crystal 21 single crystal 22 weight measuring device 23 arithmetic circuit 24 heater control device

Claims (4)

[Claims] 1. When growing a single crystal by bringing a seed crystal into contact with a melt formed by heating a raw material and pulling the seed crystal out of the melt, the diameter of the single crystal with respect to the heating temperature is controlled. The response function is obtained in advance, the predicted value of the diameter after a predetermined time has elapsed from the heating history and the diameter during the growth is obtained from the response function, and the predicted value is the diameter after the predetermined time has elapsed. In the single crystal growth method of controlling the heating temperature so as to match the target value, at least one of the time constant or the gain of the response function as the growth time of the straight body portion of the single crystal elapses. A method for growing a single crystal, which is characterized by being monotonically small. 2. The method for growing a single crystal according to claim 1, wherein at least one of the time constant and the gain monotonically decreases as the remaining amount of the melt decreases. 3. The method according to claim 1, wherein at least one of the time constant and the gain monotonically decreases as the relative position between the heating means and the melt changes. Single crystal growth method. 4. The method for growing a single crystal according to claim 1, wherein at least one of the time constant and the gain is reduced in a linear function.