JPS6243959B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a - group compound semiconductor single crystal by a liquid seal pulling method.

Gallium arsenide (GaAs), gallium phosphide (GaP),
- Group compound semiconductors such as indium antimony (InSb) and indium phosphide (InP) have characteristics such as high electron mobility, easy emission and detection of light, and operation even at high temperatures. It is becoming widely used as a material for integrated circuits, solar cells, and photoelectronic devices. Among - group compound semiconductors, GaAs single crystal has an electron mobility 5 to 6 times higher than that of silicon single crystal, and GaAs concentrating circuits that operate at high speed or with low power consumption are being actively developed. Furthermore, InP single crystals exhibit high sensitivity in the low-loss band of optical fibers used in optical communications, and are attracting attention as a material for future optical communications.

As mentioned above, in order for GaAs single crystal to be used as a crystal substrate for integrated circuits, it must have high insulating properties, be a high-quality single crystal free of physical defects such as dislocation lattice defects, and be free of chemical defects. It is required that the wafers have good internal uniformity and that large circular wafers can be obtained. A method for manufacturing GaAs single crystals that satisfies these requirements is the high-pressure liquid seal pulling method. This high-pressure liquid sealing pulling method uses low-melting glass such as boron oxide (B ₂ O ₃ ) as a sealant and melts GaAs under high pressure.
A cylindrical GaAs single crystal is formed by bringing a seed crystal into contact with the melt and pulling it up while rotating, and controlling the crystal diameter during growth compensates for the time delay in response using the crystal's weight signal. A feedback control method with added phase compensation was used. In this case, phase compensation is a method in which the amount of change in diameter after a time delay is predicted from the amount of change in the current crystal diameter calculated from the change in the weight of the crystal, and control is performed based on the predicted amount of change in diameter. However, the weight signal contained many noise components, and the predicted diameter change itself was already unreliable. Conventionally, attempts have been made to solve the prediction uncertainty in this predictive control method by improving the basic temperature program using empirical methods, but the basic temperature program itself is not universal and changes each time a crystal is pulled. It has been difficult to control the crystal diameter with good reproducibility.

An object of the present invention is to provide a method for manufacturing a cylindrical - group compound semiconductor single crystal in which the crystal diameter during growth is as close to a set value as possible and the crystal diameter is less likely to fluctuate.

When forming a - group compound single crystal using the liquid seal pulling method, the crystal diameter can be controlled using the crystal weight signal, as shown in Figure 1A, after adjusting the heater temperature. There was a time delay of L before the effect appeared (Figure 1B). Therefore, even if the temperature correction value is calculated from the amount of change in crystal diameter (dD/dt) obtained from the current weight signal and the heating temperature of the heater is controlled, the effect on the crystal diameter will start to appear after L hours. Further, the change in the growth diameter can be clearly detected after a time constant of τ (L+τ), making it impossible to perform accurate control.

In this invention, the weight of the crystal during growth and the length of the crystal pulled up are continuously measured to memorize the change pattern of the crystal shape. Next, the crystal change pattern after a predetermined time is predicted from the crystal shape change pattern traced back to the same time as the predetermined time, and the predicted shape change pattern is compared with a preset shape change pattern to determine the temperature of the heater. Set the correction value and control the heating temperature of the heater.

To explain the present invention with reference to FIG. 2, the weight of the growing crystal 1 and the length of the crystal being pulled are measured by a weight sensor 2 and a position sensor 3, and the measured values are sent to an arithmetic circuit 4. The arithmetic circuit 4 determines the diameter of the crystal based on the input measurement value and stores the change pattern.

Figure 3 shows the amount of change in crystal diameter, and the crystal change pattern a after (L + τ) time is from the current time to (L + τ).
Prediction is made based on the change pattern up to the present from the change pattern going back in time (curve b). The predicted shape change pattern is compared with a preset shape change pattern c, and a correction value for the heating temperature of the heater is determined based on the difference d.

The response of crystal diameter to temperature is expressed by equation (1).

dD/dt=K・dT/dt(1-e ^-(tL) 〓)1(t
-L) (1) where D is the crystal diameter, T is the temperature, L is the time delay, t is the time, τ is the time constant, and 1(t-L) is the unit step function.

Using the change pattern of the crystal diameter from the crystal diameter a certain time back to the current crystal diameter, the current change in diameter dD/dt ₀ can be calculated by equation (1) by curve approximation using the least squares method. Seek more.

The predicted amount of change in diameter ΔD after (L+τ) time from the current amount of change in diameter is calculated using equation (2).

ΔD=dD/dt ₀ (L+τ) ...(2) Temperature change value based on predicted diameter change amount ΔD
dT is calculated using equation (3).

dT=1/KΔD−ΔT (3) The heating temperature of the heater is corrected using the temperature correction value obtained in this way, but in this invention, the above temperature correction value is given to the heater at once. Instead of rapidly correcting the heating temperature, the heating temperature is gradually corrected so that the entire amount is output after a predicted predetermined time. When the correction time is (L+τ), the rate of change in temperature dT/dt per unit time is as shown in equation (4).

dT/dt=1/L+τ(1/KΔD−ΔT)...
(4) Figure 4A shows the case where the crystal diameter is controlled by applying the previous temperature correction value to the heater all at once, and the heating temperature of the heater is immediately increased to reach t ₀ + from t ₀
If (L + τ) is maintained, it will be delayed by l time,
Crystal diameter decreases rapidly. However, as shown in Figure 4B, the temperature correction value is given from t ₀ and t ₀ + (L+
If it is given so that it reaches its maximum value after τ) time, the change in crystal diameter will be smooth and slight.

In this invention, as described above, the heating temperature of the heater is adjusted by the arithmetic circuit 4 so that it becomes the temperature correction value after a predetermined time, and is sent to the heater temperature adjustment circuit 5.
The heating temperature of the heater is controlled over a period of (L+τ) to reach a temperature corresponding to the slow correction value.

Examples of - group compounds to which the method of the present invention is applied include GaAs, GaP, InSb, and InP.

As described above, this invention predicts the change pattern of the crystal shape after a predetermined period of time based on the change pattern traced back to that time, and compares this predicted pattern with a preset shape change pattern to determine the temperature correction value. Since the heating temperature of the heater is slowly controlled so that the heating temperature of the heater reaches the corrected value after a predetermined time, it is much more accurate than the conventional predicted value based on the amount of crystal change at that time, and the crystal diameter Since the change in is small and is carried out gradually, even if erroneous control occurs due to an error in prediction, it is easy to correct it, and the stability of control is increased.

Next, embodiments of this invention will be described.

Example: 500 g of Ga and 550 g of As were placed in a circular Vairolitec boron nitride crucible with an inner diameter of 100 mm and a depth of 130 mm.
Furthermore, 150g of B ₂ O ₃ as a liquid sealant was placed on top of it, the crucible was placed in a high-pressure container, and argon gas was injected to create a pressure of 20 atm, and the crucible was then heated to 1260°C to remove raw material elements, codes, etc. The agent is completely melted and at the top.
When the B ₂ O ₃ melt layer and the GaAs melt layer are formed at the bottom, the seed crystal is slowly lowered, and when it comes into contact with the GaAs melt layer, it is heated 10 times for 1 minute, and the crucible is moved in the opposite direction 20 times for 1 minute. The seed crystal was pulled up at a speed of 9 mm/hour while rotating at a constant rate. The predetermined time used for prediction and temperature correction was 30 minutes, which corresponded to (L+τ) time under these conditions.

The weight and length of the grown crystal are measured by a weight sensor and a position sensor and sent to a calculation circuit, and the calculation circuit records the crystal shape change pattern 30 minutes ahead.
Predict the crystal shape change pattern for 30 minutes, compare it with the preset shape change pattern, and slowly adjust the detected temperature correction value so that the entire temperature correction value is output after 30 minutes. Changed.

After about 8 hours of pulling the crystal under these conditions, the crystal was 50 mm in diameter, 100 mm in length, and weighed about 900 g.
A cylindrical GaAs single crystal was obtained, and the crystal diameter variation was within ±1%.

As a result of putting 570 g of As in excess of 500 g of Ga in the crucible and growing the crystal under the same conditions, the diameter variation of the formed single crystal was within the range of 50 mm ± 0.5 mm. 5 single crystals were created under the same conditions, but the diameter variation was ±1% in all cases.
It was within

[Brief explanation of the drawing]

Figure 1 is a graph showing the time delay in the change in crystal diameter when the temperature of the heater is increased, Figure 2 is an explanatory diagram for implementing the method of the present invention, and Figure 3 is a graph showing the amount of change in crystal diameter. The graph shown in FIG. 4 is a graph showing the relationship between the heating state of the heater and the state of change in crystal diameter. 1...Growing crystal, 2...Weight sensor, 3...
Position sensor, 4... Arithmetic circuit, 5... Heater temperature adjustment circuit, 6... Heater.

Claims (1)

[Claims] 1. Detect the crystal weight and crystal pulling length during growth, memorize the change pattern of the crystal shape, and record the change pattern after a predetermined time from the current time of the crystal shape by the same amount of time as the above change pattern from the current time. The predicted shape change pattern is compared with a preset shape change pattern to set a temperature correction value for the heater that heats the crystal raw material melt, and the temperature correction value is gradually applied to the heater. 1. A method for producing a - group compound semiconductor single crystal, characterized in that crystal growth is performed by slowly controlling the heating temperature of a heater.