JPS6086092A - Single crystal pulling device - Google Patents

Abstract

PURPOSE:In a device for pulling up single crystal by Czochralski method, to grow single crystal of inner column having good straightness in high yield, by dropping an after-heater in a washer state at a specific velocity. CONSTITUTION:The refractory 8 and the high-frequency coil 18 surrounding the platinum crucible 20 having the melt 22 placed at the center are set. A seed crystal is attached to the top of the seed shaft 10 at the top of the crucible 20, the seed crystal is immersed in the melt and cylindrical crystal is grown while the motors 12 and 17 are being rotated. The after-heater 21 made of platinum having the same material as that of the crucible 20 is set around the crystal, and in order to move the heater vertically, it is fixed to a screw rod, and the screw rod is rotated by the motor 15. Since heat is generated by the heater 21, the platinum support rod 14 is welded, and a terminal for taking out an electrode is set at the top. By the use of this device, the heater 21 is dropped at the same velocity as the dropping velocity of the liquid level 22 caused by the pulling of the crystal, and the gap between the liquid level 22 and the heater 21 is kept at an optimum value.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an apparatus for pulling single crystals using the Czochralski method, and particularly to a single crystal pulling apparatus suitable for pulling cylindrical single crystals with a high yield. It is.

[Background of the invention]

In order to grow cylindrical single crystals with good straightness and high yield using the Czochralski method, it is necessary to make the temperature gradient in the vertical direction of the melting surface large and symmetrical. In order to achieve this, ■ optimize the phase 1 position of the heating W heater case or high-frequency coil and the crucible; ■ install a washer-like thin ring on the top of the crucible (Japanese Patent Laid-Open No. 55-22
329 Publication).

Recently, increasing diameters of single crystals (50 to 75 rnIn) have been increasing with the aim of improving the yield of crystals.

As the crystal size increases, the amount of descent of the molten surface during blistering becomes even larger, and the temperature distribution inside the furnace is completely different υ at the beginning and end of blistering. Obtaining crystals was extremely difficult. In order to keep the conditions the same in the early and late stages of growth, when growing silicon single crystals, a heat shielding ring is lowered at the rate of descent of the melting surface to flatten the shape of the solid-liquid interface of the crystal and obtain uniform electrical properties. (Tokuko 51)
-47153). However, B i4'Gea01i, which is used for detection of rd and high-energy particle beams,
When growing a single crystal, simply displacing the heat shielding ring at the same rate as the rate of descent of the melting surface does not provide the optimal vertical temperature gradient, making it impossible to grow a single crystal with good straightness. .

``Even in the growth of B11z810zo and Bj1zGeOzo single crystals used for primary surface acoustic wave devices and electro-optical device materials, lowering the heat shielding ring alone cannot solve the twist in the crystal shape, and the C flaw yield decreases. The difficulty in controlling the shape of these single crystals, which mainly consist of bismuth, is due to the viscosity of the bath liquid and other oxides.

This is thought to be because it is more expensive than semiconductor materials.

[Purpose of the invention]

The purpose of the present invention is to achieve a single crystal pulling method in which the temperature gradient in the vertical direction of the melt at the beginning and end of crystal formation is the same, and the cylindrical crystal with excellent straightness is pulled with a high yield. Our goal is to provide equipment.

SUMMARY OF THE INVENTION Straight folds in crystals are strongly dependent on temperature gradients in the melt, with primarily radial and vertical temperature gradients being important. Twisting of the crystal shape is difficult to occur in the early stages of crystal pulling, and becomes more likely to occur when the melt is reduced by about half of the crucible. Therefore, we investigated the state of convection at this time using silicone oil.
71. We investigated the cause of twisting through convection visualization experiments. Figure 1 (Fig. 1) shows a convection pattern observed at the beginning of crystal pulling when the pot is full of melt. The distance between the washer-like afterheater and the solution surface is 3
In a case close to rla, convection occurs only near the surface, and almost no convection is observed in the f region. Figure 2 shows convection when the straightness of the crystal deteriorates slightly. When the distance between the washer-like afterheater and the bathing surface is 50111 m, the convection reaches the bottom of the crucible, and turbulent flow 6 is observed at the center of the solution. Therefore, a washer-like afterheater and a bath CI! i.

We investigated how the distance affects the vertical (cap) gradient of the bath solution. Figure 3 shows the vertical relationship between the surface and the bottom at the center of the solution with respect to the distance between the washer-like afterheater and the liquid surface. The relationship between the temperature difference in the direction was shown.As a result, it was found that when the distance between the washer-like afterheater and the solution surface was 15 or more, the temperature difference became smaller, and was sometimes the smallest at 50 points.

From these results, the distance between the washer-like afterheater and the solution surface was within 15fl.
It turns out that all you have to do is lower the washer-like afterheater at the same speed as the counterfeit. It was found that when a heat shield ring is installed instead of an after heater, the temperature difference is small when the distance between the heat shield ring and the solution surface is 8 m+ or more, and the effect is smaller than that of an after heater.

[Embodiments of the invention]

Next, the actual lifting device considered to implement this idea will be described using FIG. 4. In the center, a refractory 8 and a high frequency coil 18 are arranged to surround a platinum crucible 20 containing liquid a 22. There is a seed shaft at the top of the crucible, and there is a chuck at the tip to which the seed crystal can be attached, and the motors 12 and 17V (which are rotated even further) allow the seed crystal to be immersed in the melt and a cylindrical crystal can grow. In order to control the diameter of the crystal, a load cell 11 is installed to detect the weight of the crystal.

In the present invention, an after-heater 21 made of platinum, which is the same material as the rutsuho, is provided around the crystal, and is fixed to a threaded rod in order to move this heater up and down. The screw allowance is motor 1
5 allows it to rotate. In order to generate heat from this after-heater 21, as shown in FIG. 5, a support 4114 made of platinum is connected to the bath as shown in the figure, and there is a terminal at the top for connecting an electrode. A thick layer of pyroferrite 19 was provided between the fixed part of the screw rod that moves up and down and the electrode. The structure is such that the 4 degrees of the platinum afterheater is adjusted by a slider 16 and a transformer 19.

Hereinafter, an example V of crystal pulling using the above-mentioned pulling Vf apparatus of the present invention will be explained in detail.

Part 1: In this example, bismuth germanate (Bi4GeaOtz
) We will discuss the results of pulling a single crystal.

The melting point of the B14GesOtx single crystal was measured using a platinum crucible. A crystal with a diameter of 80 mm was grown from a crucible with a diameter of 150 mm. After the crystal shoulder was formed, the after-heater 21 was heated to 1100 C from the point where the diameter became constant. While maintaining the distance between the afterheater and the melting surface at 31 DI, the afterheater was lowered at the same speed as the descending speed of the melting surface, 0.4 mm/h. As shown in Fig. 5, the afterheater has a plate thickness of 0.7 mm, an outer diameter of 140 m, and an inner diameter of 105 mm. Crystal rotation speed 20
As a result of growing under the conditions of mm-1, a cylindrical crystal with good straightness could be grown, and 80% of the melt placed in the crucible could be crystallized. Until now, in order to crystallize 65% of fB, it was necessary to reduce the crystal rotation speed to 12 mm-1.

However, if the crystal rotation speed is low, a problem arises in that bubble-like defects are likely to occur in the crystal.

In the present invention, by lowering the afterheater, the temperature gradient in the vertical direction of the crucible is maintained large, so that the crystal rotation speed can be increased.

As a result, bubbles, which are defects in crystals, could be significantly reduced.

2nd example Example 1 with the distance between the near-after heater and the welding surface set to 2mm
A single crystal was grown on B14GeaOtz under the following conditions. As a result, since the distance between the after-heater and the solution surface is close, the heater may bend when the temperature of the heater is raised, and during growth, vaporized products may accumulate on the heater and come into contact with the melt, causing a short circuit, making it unsuitable for growth. Ta.

Third Example A Bi<Ge5Oxz single crystal was grown under the conditions of Example 1, with the distance between the near-after heater and the melting and melting surfaces set to 10++on. As a result, it was possible to crystallize 78% of the melt in the iribo, and to grow cylindrical crystals with good straightness.

Fourth Example A BiaGesCh2 monomorphic crystal was grown under the following conditions with the distance between the near-after heater and the bath melting surface, 1L, set to 15 mm. As a result, although the cross section of the crystal was somewhat square, 70% of the melt in the crucible could be crystallized and a single crystal with good straightness was obtained.

Fifth example B1 with the distance between the near-after heater and the melting surface set to 20m
A 4GesOtz single crystal was formed. Other formation conditions were the same as in Example 1. When about 40% of the melt in the crucible is grown, the cross section of the crystal begins to deform into a rectangular shape, and as the crystal grows, it begins to twist in such a way as to draw a tail in the direction of rotation of the crystal, resulting in good straightness. A good overall yield of crystals could not be obtained.

Sixth example: The results of pulling a bismuth slicate (B 112s 102o) single crystal will be described. Crystals with a diameter of 50 mm were formed from a crucible with a diameter of 100 mm. The distance between the after-heater and the melt was set at 3III11. The dimensions of the after-heater are 90mm in outer diameter, 78mm in inner diameter, and 0.7mm in thickness. The crystal rotation speed was 40 m-1, and the crystal pulling speed was 3 m.
After the crystal diameter in m/h reaches a predetermined size, the after-heater is turned on at a rate of descent of the melting surface of 1.1 tax/h.
It was lowered at h. 80% of the melt in the crucible
%, and crystals with good straightness were obtained.

In the above example, B 14Qes01z+Bi+zs
1Ozo, but the same bismuth-based oxide H
It goes without saying that the present device is also applicable to i4s 1sOxz + B 1t2Ue02o and the growth of these mixed crystals. Further, as shown in Example 1, the use of this apparatus has the effect that a single crystal without bubble-like defects can be grown.

〔Effect of the invention〕

By using the straight edge of the present invention, a cylindrical single crystal with good straightness can be easily formed because the surface and bottom of the center of the liquid are sharpened by a degree difference.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the σ plane of convection observed in a bath number simulation during the initial state of crystal pulling. Figure 2 is a schematic cross-sectional diagram of convection observed in a melting simulation when half of the crucible is crystallized. Fig. 3 is a graph showing the change in temperature difference between the surface and bottom of the m solution as the solution decreases, Fig. 4 is a schematic cross-sectional view showing the configuration of the single crystal pulling device according to the present invention, and Fig. 5 is the installation of the after-heater. FIG. DESCRIPTION OF SYMBOLS 1... Quartz crucible, 2... Solution, 3... Washer-like afterheater, 4... Convection pattern, 5... Solution surface, 6... Turbulence pattern, 7... Crystal, 8 ... Refractory, 9... Chamber, 10... Seed shaft,
11... Load cell for crystal weight detection, 12... Crystal rotation motor, 13... Pyroferrite, 14...
- After-heater support rod, 15... After-heater vertical movement motor, 16... Slide duck, 17... Crystal pulling upper motor, 18... - High frequency coil, 19... Transformer, 20... Platinum crucible, 21...after heater, 22...melt liquid. Kaya 1 ward pole 2 drawings

Claims (1)

[Claims] 1. In an apparatus for pulling a single crystal from a melt, an after-heater placed around the pulled crystal is lowered in accordance with the descent of the melting surface that occurs as the crystal is pulled, so that there is a distance between the melting surface and the heater. 1. A single crystal pulling device characterized by having a mechanism that maintains an optimum value. 2. In the apparatus according to claim 1, the distance between the heater and the melting surface is maintained in a range of 3 to 15 degrees, and B1
4Gea01z + B14SiaOt2+B i 1
28 j02o, B i 12 GeO20, and mixed single crystals thereof are to be pulled.