JPS6126596A - Method and deivce for pulling up crystal - Google Patents

Abstract

PURPOSE:To make stable growth of single crystal possible, by melting undoped crystal while rotating it, regulating an amount of pulled crystal and an amount of molten undoped crystal in such a way that they are always the same amount. CONSTITUTION:A crystal pulling furnace has the layshafts 11 and 12 for setting a vertically movable undoped crystal at a position eccentric from the central shaft 8 for pulling up crystal which has the same shaft as the center of a double crucible, and is in a layer between the outer periphery of the inner crucible 31 and the outer crucible 32. Crystal is pulled up by the central shaft 8 while measuring weight of pulled crystal by the metering mechanism 13, and weight of the pillar-shaped undoped crystal 10 attached to the tips of the layshafts 11 and 12 is measured by the metering mechanisms 14 and 15. While the layshafts 11 and 12 are being rotated, the lowering speed is controlled by a computer in such a way that an amount of pulled crystal from the signal from the metering mechanisms 14 and 15 and an amount of the newly dissolved undoped crystal 10 are always equal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for pulling crystals of compound semiconductors, etc., and an apparatus therefor. The method and apparatus of the present invention provide Ga m θ(In
, Si, Or etc. doped crystals and undoped crystals.
It is advantageously used in the production of compound semiconductors such as crystals), nP, and GaP. These compound semiconductors are widely used as IC substrates, optoelectronic substrates, and the like.

(Prior Art) The outline of the conventional crystal pulling method and its apparatus is as shown in FIG. 5, an example of which is shown in FIG. The surface of the cell is covered with a BtOa melt 5, and a seed crystal 6 attached to a pulling shaft 8 is immersed in the surface of the melt 4 to allow it to spread, and then the seed crystal 6 is pulled up and a single crystal 7 (e.g. GaAe etc.). Note that 1 is the furnace heater, and 2 is the susceptor (carbon).

9 is a crucible support shaft (lower shaft).

However, when growing crystals using this method, it is not possible to replenish raw materials to the melting hole, so 1) changes in the melt height change the state of convection in the melt and also change the thermal conditions. 2) When the melt contains a dopant whose distribution coefficient is not 1, the dopant concentration changes as the crystal grows.

Therefore, as shown in Fig. 4, a method of adding an appropriate amount of undoped crystal to impurities with a distribution coefficient k (1) has been considered. In Fig. 5, 7 is a growing single crystal, and 10 is a growing single crystal. The crystal being added, 4 is the raw material melt, and 3 is the melting point. However, even with this method, it is difficult to delicately control the amount of the melt, and the undoped crystal 10 that is being melted is growing. There was a drawback in that it was not possible to prevent disturbance from being applied to the single crystal 7.

That is, the lower part of FIG. 5 shows the temperature distribution on the solid-liquid interface in the radial direction of the crucible in this case, but as shown, the temperature distribution is asymmetric, and the growing single crystal 7 and
A sufficient temperature gradient cannot be established between the added crystal 10 and the single crystal 7 and the added crystal 10 may become stuck together. This is because there is no cover between the growing crystal 7 and the melting added crystal 10.

Also, as shown in Figure 5 CO), only the part of the undoped crystal 10 facing the wall of the crucible 5 melts when the crucible is opened as shown by the arrow from 4, so its cross-sectional area changes. Resulting in. In the figure, 4 is the melt and 5 is the rain.

Therefore, the amount of undoped crystal being melted cannot be controlled by the amount of descent of the vertically movable shaft to which the undoped crystal is attached.

[Problems to be solved by the present invention]

An object of the present invention is to solve the problems caused by the conventional methods as described above and to provide a stable crystal pulling method and apparatus.

[Means to solve problems]

As a means of solving the above-mentioned problems, the present invention, in crystal pulling, melts a crystal material in a concentrically arranged double crucible communicating at the bottom, and melts the crystal material in the double crucible. While pulling the crystal, the undoped crystal is rotated and melted in the annular part formed by the outer and inner melt of the double melt, and the amount of crystal pulled is equal to the amount of crystal pulled up. The present invention provides a crystal pulling method and an apparatus thereof, characterized in that the amount of undoped crystal melted is always adjusted to be the same amount.

The crystal pulling method and apparatus thereof of the present invention will be explained below with reference to the drawings. In the method of the present invention, a double crucible as illustrated in FIG. 1 is used. In FIG. 1, 51 is an inner crucible, and 32 is an outer crucible. The crucibles 32 are in communication with each other, and the inner crucible 31 and the outer crucible 32 are fixed concentrically. 4 is the raw material melt, 5 is the horse, 7 is the single crystal, a, b, c is the length and diameter of each part).

Now, the pulling furnace used in the method of the present invention is located at a position eccentric from the crystal pulling central axis 8 whose axis is the same as the center of the outer double crucible, and whose axis is the same as the center of the outer double crucible, as shown in FIG. The undoped crystal mount has a vertically movable countershaft 11, 12 in the layer between the outer periphery of the crucible 31 and the outer crucible 320. The central shaft 8 is equipped with a measuring mechanism (such as a load cell) 15 and a rotating lifting mechanism 14, and also has sub-shafts 11 and 12.
Similarly, it is equipped with measuring mechanisms (load cells, etc.) 14 and 15 and rotary lifting and lowering mechanisms 17 and 18, respectively. Measuring mechanism 13
The weight measurement signals from ~15 are input to the computer mechanism, and the computer uses this signal to control the multi-rotation lifting mechanism 1.
6 to 18 can be controlled.

In the method of the present invention, the crystal is pulled by the central shaft 8 while the weight of the pulled crystal is measured by the measuring mechanism 1S, and the weight of the columnar undoped crystal 10 attached to the tip of the rotating sub-shaft 11. This is done while measuring with the weighing mechanism 14.15. The countershaft 11°12 rotates while the measuring mechanism 14.1
The rate of descent is controlled by the computer so that the amount of undoped crystal 10 to be newly melted is always equal to the amount of undoped crystal 10 that is pulled up according to the signal from 5. In addition, the first
Numbers common to the figures refer to the same parts; 9 is the bottom axis of the collar, 1 is
9 means the furnace body.

The advantages of the method of the invention are as follows.

■ As shown in FIG. 5 (5), in the method of the present invention, the minor axis supporting the undoped crystal 10 rotates, so the undoped crystal 10 melts symmetrically and stably, so that the cross-sectional area does not change as in the conventional method. There is no. Note that the reference numbers in the figure have the same meanings as in the case (in FIG. 6).

■ Since both the center axis and sub-axis are equipped with measuring mechanisms, the amount of pulled crystal and the amount of melted undoped crystal can be measured accurately. Based on this, the moving speed of each axis can be accurately and precisely controlled, so that the melting rate is always high. The amount of raw material melt inside can be kept constant. Alternatively, the concentration of a certain impurity in the melt can be made constant, and the amount of the melt can be kept almost constant.

■ By using a double layer to separate the pulled crystal from the undoped crystal, the temperature distribution is symmetrical and crystal growth is not disturbed by the undoped crystal.

Here, a method for keeping the amount of melt constant will be explained.

For example, the velocity V of the minor axis with the undoped crystal is determined so that the following equation (1) holds for the increment (÷) of the weight (W) of the crystal per unit time. However, due to the influence of buoyancy etc. , the true weight increase is determined by removing it by computer calculation etc.

W ''' p, Sv ae++ (1) at Here, P8 is the specific gravity of the undoped crystal, and S is its cross-sectional area.

Furthermore, when you want to maintain a constant concentration of a certain impurity (for example, In) in the melt, the distribution coefficient is 1. The concentration in the melt is C1. The amount of melt w4. The weight of the undoped crystal is "sub", then "Pub=ρ8SvIdt W aw = −at at W Therefore, ρB Sv = (1k) a, ” '
” (3) Here, since k(1), the amount of melted liquid is twice as small as normal.

Therefore, V may be determined so that equation (3) holds true.

The inner crucible of the double crucible used in the crystal pulling method of the present invention has a diameter that is 30 to 100 inches larger than the crystal diameter, and the outer crucible has a diameter that is 30 to 60 inches larger than the inner crucible. Use one with .

Materials for double ruriho include quartz, boron nitride,
Any of those commonly used for crystals such as silicon nitride and aluminide may be used.

In addition, although the case in which the pulling furnace has two subshafts is illustrated in the above explanation, it is not limited to this, and the O subshaft may have either one or two or more. are, for example, load cells, strain gauges, etc.

(Example) In a quartz crucible (outer crucible) with 100 inte φal as shown in Fig. 1, a quartz crucible with 6 inteφ(b) (
A double layered Ruriho with an inner crucible fused together was used. The inner tube communicates with the outer tube through a 4-inch φ (C) hole near its bottom. A GaAs crystal was pulled up using the double rutsuho. The configuration of the pulling furnace used was that shown in Figure 2.

G&AI! 4ky and In6 Of 'eThe double crucible was charged inside, and %016001F was put into the inner crucible and %011200f was put into the outer crucible. GaA3 and I
The melt volume of n was about 1 inch and the layer was about 1 inch thick. GaAs undoped polycrystals with a diameter of 1.5 inches and a length of about 30 crn are attached to two sub-shafts separated by about 113 cm from the central axis. At n, Oll was controlled by computer.

As a result, a 6-inch crystal of approximately 4k17 (GaAs, engineering
Dawg). The crystal dislocation density from the front to the back of this crystal was all 1000/1 or less.

〔Effect of the invention〕

In general pulling, the melt depth changes as the crystal grows, which greatly affects the crystal properties (dislocation density, etc.). The thermal environment at the solid-liquid interface changes significantly. (1c
If the tn solid-liquid interface is different, in the case of a 6-inch crucible, 10°/
cm - 50°/ctn The temperature gradient in the axial direction changes) Furthermore, when the melt depth changes, the convection in the melt also changes significantly.

In the present invention, this does not occur and a crystal with uniform properties from the front to the back can be obtained.

In addition, when doping with impurities, if the solidification rate is
As shown in the following equation (4), Os = ko@ (1-
x)k-s ``''(4) F>, which varies greatly depending on x, but according to the present invention, when k<1, OB can be approximately constant from the front to the back.

As described in detail above, the method and apparatus of the present invention enable stable single crystal growth, and can be widely used in the field of crystal manufacturing.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a double crucible used in the crystal pulling method of the present invention. FIG. 2 is a diagram schematically explaining the crystal pulling method and apparatus of the present invention. FIG. 3 is a diagram illustrating crystal pulling by a conventional method. FIG. 4 is a diagram illustrating an asymmetric melting curve of an undoped crystal according to a conventional method, and the lower part of the diagram shows the temperature distribution on the solid-liquid interface in the radial direction of the melt in that case. FIG. 5(6) is a diagram comparing the method of the present invention and the conventional 031tli method in terms of how undoped crystals dissolve.

Claims (2)

[Claims] (1) In crystal pulling, the crystal material is melted in double crucibles arranged concentrically and communicating at the bottom, and while pulling the crystal from the inner crucible of the double crucible, Crystal pulling is performed by rotating and melting an undoped crystal in an annular portion formed by an outer crucible and an inner crucible, and adjusting the amount of the crystal pulled and the amount of the undoped crystal melted so that the amount is always the same. Method. (2) at least a) a concentrically arranged double crucible communicating at the bottom; b) a central axis having a rotary lifting means disposed in the inner crucible of the double crucible; c) eccentric from the central axis. d) a subshaft having one or more rotating lifting means located at the position and in the annular part formed by the outer crucible and the inner crucible of the double crucible; d) metering means installed on the central axis and the subshaft; A lifting device having:
A crystal pulling device comprising means for controlling the rotary elevating means based on data measured by the measuring means.