JPS5935879B2 - Method for manufacturing compound semiconductor single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to the production of semiconductor single crystals of ■-V group compounds such as GaP, GaAs, and InP, which have high melting pressures, by controlling them into a predetermined shape and by a liquid capsule pulling method. It's about how to do it.

Technical Background of the Invention and Its Problems GaP single crystal, which is a compound semiconductor single crystal containing volatile substances, is an important material as a substrate for visible light emitting diodes, and is usually produced under high pressure by the liquid encapsulation method (LEC method). It is made.

In this method, the surface of a raw material melt of a compound is covered with an inert liquid such as B2O3, and then a single crystal is pulled while pressurizing the surface with an inert gas higher than the decomposition pressure of the compound. Controlling the crystal diameter is also an important issue in the LEC method, but the factors that vary the diameter are more complex than those for silicon and oxide crystals that are pulled using the regular Czyochoralski method.
The problem is that diameter control is extremely difficult. Optical methods and gravimetric methods are commonly used to detect diameters, and are applied to silicon and oxide single crystals. In addition to the LEC method, an X-ray method has also been proposed. The diameter deviation detected by these methods is usually fed back to the heating power of the crucible, and the melt temperature is adjusted to control the diameter. Incidentally, in recent years, there has been a demand for large-diameter, high-quality single crystals of 2.5 inches to 3 inches or more for ■-V group compound semiconductor single crystals. It has become necessary to manufacture single crystals by making them as loose as possible.

However, as the temperature gradient is made gentler, the crystal growth becomes irregular, the crystal diameter does not change uniformly, and polycrystals and twins are more likely to occur, leading to deterioration in crystal shape and quality.

Therefore, under a low temperature gradient, it is difficult to obtain high-quality single crystals with a good yield using the conventional method of controlling the diameter using only temperature, which has the drawback of not being able to meet the above requirements. Purpose of the Invention The present invention has been made in view of the above points, and
The object of the present invention is to provide a method for manufacturing a high-quality single crystal with a controlled diameter by eliminating the above-mentioned drawbacks when manufacturing a compound semiconductor single crystal by the EC method.

Summary of the Invention As a result of various investigations into the causes of the above-mentioned problems, the present inventor found that when pulling a single crystal under a low temperature gradient, the thermal environment inside the crucible changes significantly as the melt decreases, and the temperature gradient I thought that this was because it became too loose.

Further research revealed that there is a strong correlation between the rotational speed of the crystal, the irregular diameter change of the crystal, and the temperature gradient.

FIG. 1 shows this situation, where 1 is a pulled single crystal, arrow A indicates the crystal rotation direction, and arrow B indicates the crucible rotation direction. FIG. 1b shows a state in which the single crystal rotation is proper. Now, assuming that the case where the crucible rotation direction and the crystal rotation direction are the same is considered to be a positive direction, when the rotation speed of the crystal increases in the positive direction, the diameter of crystal 1 becomes thicker as shown in Figure 1 c, and conversely increases in the negative direction. When this happens, the diameter of the crystal 1 becomes thinner as shown in FIG. 1a. FIG. 2 shows its response characteristics.
Based on this, when the diameter deviation was fed back to the crystal rotation speed, irregular diameter changes, polycrystals, and twin crystals in the GaP crystal were significantly reduced, and stable diameter control was achieved even under low temperature gradients. It turned out to be quite effective. Therefore, the single crystal manufacturing method of the present invention includes a detection circuit that detects the diameter deviation of the pulled crystal from a predetermined value, and an arithmetic circuit that calculates the crystal rotation speed from the diameter deviation using a predetermined formula. The present invention is characterized in that it is equipped with a rotation speed control circuit for controlling the crystal rotation speed, and pulls a single crystal by feeding back the diameter deviation to the rotation speed of the seed crystal.

Examples of the invention An embodiment of the present invention will be described below based on the drawings.

FIG. 3 is an example of a GaP single crystal manufacturing apparatus equipped with the functions according to the present invention. In the figure, 11 is a GaP melt, 12 is a liquid capsule, 13 is a seed crystal, 14 is a GaP crystal, 15 is a crucible, 16 is a heating heater, IT is a crystal rotation axis, 18
19 is a crystal rotation motor, 19 is a crystal weight detector, 20 is a crystal rotation speed control circuit, 21 is a crystal rotation speed calculation circuit, 22 is a crystal diameter deviation detection circuit, and 23 is a heating device. Inner diameter 10
After charging 900 y of GaP raw material and 200 y of liquid capsule (B2O3) into crucible 15 of 0 Murei φ, pressurizing with nitrogen gas (~ 60 k9/Cd) and melting, the initial temperature gradient at the solid-liquid interface was set to 80 y. C/CTrL, the crystal rotation speed was set to 3 rpm, the crucible rotation speed was set to 20 rpm, and the pulling speed was set to 12 mwL/h to start crystal pulling. After the crystal reached a predetermined diameter, the deviation determined by the crystal weight detector 19 and the crystal diameter deviation detection circuit 22 was input to the crystal rotation speed calculation circuit 21, and the crystal rotation speed Rs was calculated by the following formula. The rotation speed thus obtained was input to the crystal rotation speed control circuit 20, and the rotation speed of the crystal rotation motor 18 was changed to feed back the diameter deviation to the crystal rotation speed while continuing crystal pulling. The crystal did not have small diameter variations such as irregular protrusions, the crystal surface was smooth, and the diameter variation was ±1n or less.

When the crystal was pulled five times in succession, no occurrence of polycrystals or twins was observed, and the crystal could be pulled with a yield of almost 100%. Here, diameter control is also performed at the same time by changing the heating power using a normal method. On the other hand, when we pulled the crystal by keeping the rotational speed constant and controlling the diameter using only the temperature, the crystal was good from the shoulder to the first half, but in the second half, the diameter changed at small intervals and the crystal was pulled. There were horn-like protrusions on some parts.

At this time, the diameter change was as much as ±3 mm, and good results could not be obtained. According to the method described above, a GaP single crystal could be produced stably and with good reproducibility even under a low temperature gradient.

Note that the calculation of the crystal rotation speed Rs using the above equation (1) may be performed using a computer, a calculator, or any other calculation method.

Also, the formula used to calculate the crystal rotation speed Rs is not necessarily (
1) It is not limited to the formula, and other control formulas or experimental formulas may also be used. The method of the present invention also applies to other single crystals to which the liquid capsule pulling method can be applied, such as Ga
It can be similarly applied to As, Inp, GaSb, etc., and the effects obtained are also great.

Effects of the Invention As explained above, according to the present invention, the following effects can be obtained in the liquid capsule pulling method.

(1) By using this method in combination with a diameter control method that changes the heating power, highly accurate diameter control can be performed stably and with good reproducibility even under low temperature gradients. (2
) The improved diameter accuracy increases the yield of wafers from raw materials, which is about 10% or more better than conventional methods.

(3) Almost no polycrystals or twins are observed, and the crystal production yield is improved by about 20% compared to conventional methods.

(4) Productivity is improved by industrially applying the present invention.

The present invention is particularly effective in producing high-quality single crystals with controlled diameters under low temperature gradients.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the correlation between changes in crystal rotation speed and crystal shape, FIG. 2 is a diagram also showing the response characteristics of diameter deviation due to changes in crystal rotation speed, and FIG. FIG. 2 is a configuration diagram for explaining an example. 11...GaP melt, 12...Liquid capsule, 13...Seed crystal, 14...G
aP crystal, 15... Crucible, 16...
Heater, 17...Crystal rotation axis, 18...
... Crystal rotation motor, 19 ... Crystal weight detector, 20 ... Connection rotation speed control circuit, 21 ...
. . . Crystal rotation speed calculation circuit, 22 . . . Crystal diameter deviation detection circuit, 23 . . . Heating device.

Claims (1)

[Claims] 1. When manufacturing a compound semiconductor single crystal by the liquid capsule method, a detection circuit that detects a diameter deviation from a predetermined value of a pulled single crystal, and a detection circuit that detects a diameter deviation from a predetermined value of the pulled single crystal, and a It is characterized by comprising an arithmetic circuit that calculates the rotation speed and a control circuit that controls the crystal rotation speed, and pulls the single crystal in a predetermined shape by controlling the rotation speed of the pulled single crystal according to the diameter deviation. A method for manufacturing a compound semiconductor single crystal. 2. The method for manufacturing a compound semiconductor single crystal according to claim 1, wherein the detection circuit determines the diameter deviation based on a weight change of the pulled single crystal. 3 The arithmetic circuit calculates the crystal rotation speed Rs based on the following formula.
A method for manufacturing a compound semiconductor single crystal according to claim 1, which requires the following. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ However, Rso: Preset rotation speed K: Feedback gain ΔD_i: Diameter deviation Δt: Unit time 4 The temperature gradient inside the crucible for pulling the single crystal is 2
．． 2. The method for producing a compound semiconductor single crystal according to claim 1, wherein the temperature gradient is low enough to obtain a large-diameter, high-quality single crystal of 5 to 3 inches or more.