JPS6018634B2 - Crystal pulling device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises an outer crucible containing a molten raw material, and an inner crucible disposed within the outer crucible, and the outer crucible is passed through a through hole provided in a wall of the inner crucible. Regarding a crystal pulling device configured to grow and pull a crystal from the molten raw material supplied in the inner crucible, the molten raw material in the crucible is particularly applicable to a device for pulling and growing a rod-shaped silicon single crystal. This is what we provide.

Conventionally, when a semiconductor single crystal is grown from a melt in a crucible by the Czochralski method (CZ method), the impurity concentration distribution in the length direction of the grown single crystal is C=
It is expressed as kCo(1-G)k-1 (where k is the segregation coefficient, Co is the initial impurity concentration of the melt, and G is the solidification rate).

Therefore, the impurity concentration distribution in the length direction of the grown single crystal changes greatly, especially when k is small, which significantly reduces the yield of single crystals having the required impurity concentration. To solve these problems, a method called the floating crucible method has already been proposed and has been applied to the growth of single crystals of germanium.

To explain this with reference to FIG. 1, in the quartz tube 1, an inner graphite crucible 3 as a floating crucible is arranged in an outer graphite crucible 2, and molten germanium 4 contained in the crucible 2 is placed at the bottom of the crucible 3. The crucible 3 is fed into the crucible 3 through the small hole 5, and just when equilibrium is reached, the crucible 3 floats in the molten germanium 4 and stops. In this state, impurities are added to the crucible 3, and the seed crystals 8 held by the chuck 6 are successively pulled up. In this floating crucible method, the raw material molten germanium 4 is supplied from the outer crucible 2 through the small hole 5 at a constant rate, and the single crystal is drawn while adjusting the amount of molten germanium in the floating crucible 3 to be constant. can be raised. As a result, the impurity concentration C in the single crystal is C = kCoe-km'mi (where k is the polarization coefficient, Co is the initial impurity concentration in the floating crucible, m is the amount of germanium pulled, and mi is amount of germanium in the floating crucible). As can be seen from this equation, if the value of k is 0.1 or less, the impurity concentration will not decrease much even if the pulling progresses. However, when the above-mentioned floating crucible method is applied to the growth of silicon single crystals, there is a risk that the raw material molten silicon may react with the graphite in the crucibles 2 and 3, leading to the destruction of the crucibles 2 and 3. be.

Therefore, first of all, due to problems with the material of the crucible, the conventional floating crucible method cannot be applied to the growth of silicon single crystals, and was thought to be suitable only for germanium. Quartz is currently considered to be the best crucible material for growing silicon single crystals, but an attempt was made to construct crucibles 2 and 3 of quartz in the apparatus shown in Figure 1 to pull silicon single crystals. For example, there are the following problems.

That is, when the crucible 3 in FIG. 1 is lowered, the outer crucible 2
Because the outer circumferential surface of crucible 3 and the inner circumferential surface of crucible 2 are quite close to each other due to the guided relationship, quartz and quartz, that is, crucibles 2 and 3, are separated under the melting point (142030) of the molten silicon in the crucible. The crystals adhere to each other or become deformed, making it impossible to grow a silicon single crystal. In addition, since the crucible 3 with low specific gravity is suspended,
If the crucible 3 is not pressed down from above as the silicon single crystal is pulled up, there is a risk that the crucible 3 will not descend (sink) to a predetermined depth position. However, in this case, when the crucible 3 is pressed down, it deforms or changes its position, making the operation cumbersome and inaccurate. The inventors of the present invention have found that the main cause of these defects is that the inner crucible 3 is not fixed and is placed close to the outer crucible 2, and has arrived at the present invention.

That is, the present invention provides, in the crystal pulling apparatus described at the beginning, (a'a) a position sufficiently distant from the outer crucible so that the inner crucible does not adhere to the outer crucible due to heat. be located in

'b--Comprising a moving means for keeping the liquid level of the molten raw material in the inner crucible substantially constant by moving the inner crucible downward relative to the outer crucible while holding the inner crucible; thing.

This relates to a device characterized by:

With this configuration, a single crystal with a uniform impurity concentration distribution, particularly a silicon single crystal, can be reliably obtained. Next, an example in which the present invention is applied to the growth of a silicon single crystal will be described with reference to FIGS. 2 and 3.

First, the configuration of the single crystal pulling apparatus according to this embodiment will be explained with reference to FIG. According to this device, a graphite crucible 10 is fixed in a water-cooled stainless steel housing 11 on a collar shaft 19 that can move up and down.
An outer quartz crucible 12 is disposed closely on the inner surface of the crucible. Therefore, this crucible 12 is reinforced (held) by the crucible 10. Inside the outer quartz crucible 12 , an inner quartz crucible 13 having a small hole 15 at its bottom is arranged at a distance of one skin or more from the crucible 12 , and the molten silicon 14 contained in the crucible 12 passes through the small hole 15 . Crucible 13
It is also supplied internally. Inner crucible 13
A collar portion 20 is integrally provided on the upper edge, and a heat-resistant holder 21 made of molybdenum is iron-bonded to the collar portion.
A support rod 22 is fixed to. Therefore, the inner crucible 1
3 is immersed in the molten silicon 14 while being fixed in position by a support rod 22 via a holder 21. The support rod 22 is configured to be able to rotate and move up and down while holding the crucible 13 in this manner, and the crucible 13 that follows the movement of the support rod can be rotated or moved up and down to come to a predetermined position. Its position can be changed. When growing a silicon single crystal, the seed crystal 17 held by the chuck 16 is immersed in the molten silicon 14 in the crucible 13 and pulled up while growing the silicon single crystal 18.

According to this pulling up, the amount of molten silicon 14 in the inner crucible 13 decreases. To compensate for this decrease, the inner crucible 13 is lowered by a predetermined distance by lowering the support rod 22, or the outer crucibles 12 and 10 are raised by a predetermined distance by raising the crucible shaft 19. With this operation, the molten silicon 14 in the outer crucible 12 becomes
It is replenished into the inner crucible 13. Therefore, the amount of molten silicon in the crucible 13 can always be kept constant, and the liquid level can always be kept constant. If this liquid level fluctuates, the impurity concentration in the silicon changes too much, which causes variations in the impurity concentration distribution in the length direction of the obtained silicon single crystal, making it impossible to obtain a uniform one. According to the example, such a situation can be prevented and a single crystal with a substantially uniform impurity concentration can be grown at all times, and a single crystal with a uniform impurity concentration up to about 90% of the input amount can be obtained. Note that at the beginning of the operation, predetermined impurities are placed in the inner crucible 13, and then molten silicon is allowed to flow from the outer crucible 12 through the small hole 15, so that only the molten silicon in the inner crucible 13 is can be doped with impurities.

What is important in this embodiment is that the inner crucible 13 is placed at a sufficient distance of one skin or more from the outer crucible 12, so that the heat of the molten silicon 14 causes the crucibles 12 and 13 to adhere to each other. This can effectively prevent conflicts.

However, the inner crucible 13 supports the support rod 22 through the retaining odor 21.
Since the crystals are held in place by the crystals, they will not be deformed by heat, and therefore the silicon single crystal growth operation can be carried out smoothly. Furthermore, since a mechanism is provided in which the inner crucible 13 is lowered a predetermined distance while being held, or the outer crucible 12 is raised a predetermined distance, the amount of molten silicon in the inner crucible 13 (the liquid level It is possible to keep the impurity concentration in the growing single crystal constant by keeping the impurity concentration constant.
This also makes it possible to prevent swirl defects from occurring in the pulled single crystal. The descending speed of the brim 13 and the ascending speed of the crucible 12 can generally be determined by the ratio of the cross-sectional area of the grown single crystal 18 to the cross-sectional area of the outer crucible 12. Next, a specific example of this embodiment will be described.

The silicon input amount was 8k9, and a 3″◇ silicon single crystal doped with boron as an impurity was grown.

Figure 3 shows the resistivity at the pulled interface of the obtained single crystal. In the figure, the white circles represent the resistivity distribution (theoretical value) according to the conventional method, and the black circles represent the resistivity distribution according to this example ( (experimental values). According to this, as the pulled weight increases, that is, in the length direction of the pulled single crystal, in the conventional case, the resistivity decreases (that is, the impurity concentration increases), whereas in the case of this example, the resistivity decreases (that is, the impurity concentration increases). It can be seen that the resistivity (ie, impurity concentration) distribution is approximately uniform. This is because phosphorus (k=0.35), which has a small polarization coefficient, is an impurity.
It has been proven that the effect is even greater. Although the present invention has been described above with reference to one embodiment, this embodiment can be further modified based on the technical principles of the present invention.

For example, even if the crucibles 13 and 12 are lowered or raised simultaneously, the same effect as described above can be obtained. Matata Crucible 13
, 12 may be changed, and their arrangement and shape may also be changed. 4/hole 1 provided in crucible 13
A plurality of crucibles 5 may be present, and their formation position may not be at the bottom of the crucible 13 but at the side (side wall). Further, the materials of other components can be changed, for example, the holder 21 and the holding rod 22 may be made of other materials that can withstand high temperatures. Note that the present invention is also applicable to the growth of other single crystals. As described above, in the present invention, the inner crucible is placed at a sufficient distance from the outer crucible so that they do not stick to each other, and is moved while being held.
Adhesion of both crucibles and deformation of the inner crucible can be effectively prevented, and crystal growth operations can be performed favorably.

However, by lowering the inner crucible relatively, the liquid level of the raw material in the inner crucible is kept constant, so the impurity concentration in the growing crystal can always be uniform, and this uniformity can be maintained. It is possible to reliably obtain a suitable impurity concentration distribution.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an apparatus for carrying out a conventional floating crucible method. 2 and 3 show an embodiment in which the present invention is applied to the growth of a silicon single crystal, in which FIG. 2 is a cross-sectional view of a single crystal pulling apparatus, and FIG. It is a graph showing the change in resistivity at the pulled interface depending on the pulled weight in comparison with a conventional one. In addition, in the symbols used in the drawings, 12... outer quartz crucible, 13...
・Inner quartz crucible, 14... Molten silicon, 17...
・Seed crystal, 18...Silicon single crystal, 19...Crucible shaft, 20...Brim portion, 21...Retained odor, 22...
・I support you. Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. An outer crucible containing a molten raw material and an inner crucible disposed within the outer crucible, wherein the melt in the outer crucible is passed through a through hole provided in a wall of the inner crucible. In a crystal pulling apparatus configured to grow and pull crystals from a molten raw material supplied into the inner crucible, (a) the inner crucible may adhere to the outer crucible due to heat. The crucible is located at a sufficient distance from the outer crucible to prevent (b) comprising a moving means for maintaining the liquid level of the molten raw material in the inner crucible at a substantially constant level by moving the inner crucible downward relative to the outer crucible while holding the inner crucible; . A device featuring: