JPH0753294A - Method for growing silicon single crystal - Google Patents

Abstract

PURPOSE:To obtain a silicon single crystal with one time of FZ stage from a silicon raw material rod. CONSTITUTION:One end of the silicon raw material rod 1 is immersed into molten silicon 3 and is partially melted; thereafter, the silicon raw material rod is pulled up to form a cone part 2 of long crystal grains which are recrystallized. The silicon raw material rod 1 is partially heated to melt with this cone part 2 as a starting point to form a molten zone 5. This molten zone 5 is moved from one end to the other end of the silicon raw material rod 1 while a static magnetic field is impressed thereto, to grow the silicon single crystal 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a method of growing by a method (float zone method or floating zone melting method). More specifically, it relates to a method for growing a silicon single crystal from a silicon raw material rod in one FZ step.

[0002]

BACKGROUND OF THE INVENTION FZ method and CZ method (Czochralski method) are mainly used as a method for growing a silicon single crystal. The FZ method is a high-purity silicon which is less contaminated by impurities than the CZ method. It has a feature that a single crystal can be grown, and is advantageous when manufacturing a high-resistance silicon single crystal for the purpose of manufacturing a high power semiconductor device.

In the case of growing a silicon single crystal by the FZ method, first a polycrystal of silicon having a mean particle size of 10 μm to 1000 μm is vapor-phase grown on a silicon core rod using trichlorosilane as a raw material to manufacture a silicon raw material rod, and one end of the rod is manufactured. Is processed into a conical shape (hereinafter, this portion is referred to as "cone portion"). Then, the tip of the cone portion is melted and fused with the seed crystal, and the silicon raw material rod and the seed crystal are integrated while dislocation-free by a seed drawing.

Next, using a ring-shaped induction heating coil, the silicon raw material rod is partially heated and melted starting from the fused portion of the seed crystal, and the silicon raw material rod (polycrystal) and the single crystal are coaxially or polarized. Re-crystallize the silicon raw material rod while rotating it around the core axis and moving it relative to the induction heating coil, gradually moving the partially generated melting zone from the cone part to the other end of the silicon raw material rod. By doing so, a silicon single crystal is obtained.

[0005]

Conventionally, when a silicon single crystal is grown by the FZ method, a step of heating and melting a silicon raw material rod by an induction heating coil to move the melting zone from the cone portion to the other end (FZ step) Was usually performed twice to obtain a silicon single crystal. This is because it is difficult for the silicon raw material rod to be completely single-crystallized in the first FZ step, and the intermediate silicon polycrystalline rod is grown in the first FZ step (prezoning) and the second FZ step (dislocation free). Zoning), a silicon single crystal ingot was grown by using an intermediate silicon polycrystal ingot as a raw material rod.

However, since the FZ process requires a considerable amount of time to perform once, performing the FZ process twice is disadvantageous in terms of production efficiency in manufacturing a silicon single crystal. Therefore, by applying a static magnetic field during the FZ process,
There is a method of obtaining dislocation-free silicon single crystal in a single process. In this method, the convection of molten silicon in the melting zone is suppressed by a static magnetic field, so that the time until the polycrystalline grains separated in the melting zone reach the solid-liquid interface on the single crystal side is increased. Is completely melted to suppress crystal disorder in the single crystal growth site.

However, even in such a method of applying a static magnetic field, only 70% of single crystals are formed in one FZ step, and two FZ steps are also performed in order to obtain a higher single crystallization rate. There was a need.

Therefore, an object of the present invention is to provide a silicon single crystal growth method capable of growing a dislocation-free silicon single crystal at a high single crystallization rate in one FZ step.

[0009]

According to the present invention, a silicon raw material rod is partially heated and melted to form a molten zone, and the molten zone is moved from one end portion to the other end portion of the silicon raw material rod. In the method for growing a silicon single crystal by the FZ method for growing a single crystal, one end of the silicon raw material rod is immersed in molten silicon to partially melt and then pulled up to form a conical recrystallized portion (cone portion). There is provided a method for growing a silicon single crystal, which is characterized in that the silicon single crystal is grown by the FZ method while applying a static magnetic field to the melting zone with the recrystallization portion as a starting point.

The recrystallized portion is formed of silicon polycrystal containing crystal grains having a length of 1 mm or more. Further, a conical portion is formed in advance at one end of the silicon raw material rod, and a portion of the conical portion having a cross-sectional diameter of at least 60 mm or more at the tip end side is immersed in the molten silicon to be melted. It may be pulled up later to form a recrystallized portion.

[0011]

According to the present inventors, the state of the melting zone is different between the cone portion of the silicon raw material rod and the straight body portion, and there is no dislocation in the growth of the cone portion of the silicon raw material rod, which is the starting point of growth, in the FZ method. It was found to be extremely important in obtaining a silicon single crystal.

3 and 4 show a silicon raw material rod 1 respectively.
FIG. 4 is a partial cross-sectional view showing a state of a melting zone 5 in the straight body portion and the cone portion of FIG.

The silicon raw material rod 1 has an average particle diameter of 10 μm
Since it has a polycrystalline structure consisting of crystal grains of 1000 μm, at the solid-liquid interface 9 on the raw material rod side, in addition to the crystal grains 7 that melt in situ, it also separates from the grain boundaries of the silicon raw material rod 1 and enters the melting zone 5. After that, there are crystal grains 7 that are not melted. These crystal grains 7 are melt zones 5 when the static magnetic field is not applied.
It is entrained in the convection inside and settles downward while being accelerated,
If it reaches the solid-liquid interface on the single crystal side without being completely melted as it is, the growing single crystal becomes polycrystal.

When a static magnetic field is applied to suppress convection in the melting zone 5, the crystal grains 7 float in the melting zone 5 for a long time, so that the crystal grains 7 reach the solid-liquid interface 6 on the single crystal side. It becomes easy to melt. Particularly, in the straight body portion of the silicon raw material rod 1 as shown in FIG. 3, the melting zone 5 formed by heating and melting the silicon raw material rod 1 by the induction heating coil 4 has a large diameter, and the solid liquid on the raw material rod side is large. Since the interface 9 and the solid-liquid interface 6 on the single crystal side maintain a relatively large distance, the crystal grains 7 are completely melted by the time they reach the solid-liquid interface 6 on the single crystal side, and many single crystals are growing. It is possible to prevent crystallization.

However, in the cone portion of the silicon raw material rod 1 as shown in FIG. 4, the diameter of the melting zone 5 is smaller than the diameter of the melting zone 5 in the straight body portion, and the solid-liquid interface 9 on the raw material rod side does not exist. The distance from the solid-liquid interface 6 on the single crystal side is short. As a result, even when a static magnetic field is applied to suppress convection, the crystal grains 7 freed from the grain boundaries of the silicon raw material rod 1 reach the solid-liquid interface 6 on the single crystal side before they are completely melted, and during the growth. Dislocations were generated in the single crystal and further became a cause of polycrystallization.

Therefore, in the present invention, one end of the silicon raw material rod is immersed in molten silicon to partially melt it and then pulled up to be recrystallized, and a cone made of relatively large crystal grains having a length of 1 mm or more. To form a part. Large crystal grains having a length of 1 mm or more are all melted at the solid-liquid interface on the raw material rod side without being separated from the grain boundaries. Therefore, a silicon single crystal having no dislocation even in the cone portion can be obtained.

When the melting zone moves from the cone portion of the silicon raw material rod to the straight body portion, the grain boundaries become crystal grains having a small grain size. The distance of the solid-liquid interface on the single crystal side becomes sufficiently large, and even if the crystal grains are separated from the grain boundary, they are completely melted by the time they reach the solid-liquid interface on the single crystal side, so that dislocation does not occur.

As described above, in the present invention, only the cone portion is melted, pulled up, and recrystallized to perform one F
A dislocation-free silicon single crystal is obtained in the Z step. Moreover, since the straight body portion (main body portion) of the silicon raw material rod may be polycrystalline silicon with a small grain size obtained by a usual method, the process can be simplified.

In the present invention, since the cone portion of the silicon raw material rod is formed when it is immersed in molten silicon and pulled up, it is not necessary to form the cone portion in advance.
The end of the original silicon raw material rod may have any shape. Therefore, it is not necessary to process the silicon raw material rod to form the cone portion as in the conventional case, and the machining cost can be saved.

As described above, it is not necessary to previously form the cone portion at the end of the silicon raw material rod, but it goes without saying that a silicon raw material rod in which the cone portion is previously formed may be used. In that case, if the preformed cone portion has a cross-sectional diameter of at least 60 mm or more, only the portion on the tip side of the cross-sectional portion is immersed in molten silicon for melting, and then pulled up to form a recrystallized portion. The part that melts the raw material rod can be relatively small. This is because the solid-liquid interface on the single crystal side becomes sufficiently deep when the molten zone is formed in the portion where the diameter of the cone portion exceeds 60 mm.

The molten silicon used in the present invention may be one obtained by melting polycrystalline silicon, or one obtained by melting pieces of silicon raw material rods collected.

[0022]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is a process chart showing an embodiment of a method for growing a silicon single crystal according to the present invention. As shown in FIG. 1A, as the silicon raw material rod 1 used in this embodiment, a silicon raw material rod 1 which does not have a cone portion used in a usual method is used.

One end of this silicon raw material rod 1 is immersed in molten silicon 3 obtained by heating and melting polycrystalline silicon at a melting point temperature of silicon or higher, and the one end is melted (FIG. 1).
(B)). Then, the silicon raw material rod 1 is gradually pulled up as in the CZ method to recrystallize the one end to form the cone portion 2 (FIG. 1C). The crystals of the cone portion 2 thus formed can have a large crystal grain length of 1 mm or more.

Next, as described above, the silicon raw material rod 1 having the relatively large polycrystalline cone portion 2 having a long crystal grain is described.
Using, the silicon single crystal 8 is grown by the FZ method.
Specifically, a seed crystal (not shown) is provided at the tip of the cone portion 2.
300 to 1000 gauss on the melting zone 5 after fusing
While applying the static magnetic field, the silicon raw material rod 1 is gradually moved from the upper side to the lower side so as to pass through the hollow portion of the induction heating coil 4, and the melting zone 5 is moved from the cone portion 2 of the silicon raw material rod 1 to the upper end direction. Let The static magnetic field applied to the melting zone 5 may be a vertical magnetic field or a horizontal magnetic field.

The single crystallization rate of the silicon single crystal obtained by performing the single crystallization step by the FZ method once was 85% or more. On the other hand, the single crystallization rate of the silicon single crystal obtained by performing the single crystallization step by the FZ method once without using the static magnetic field using the original silicon raw material rod 1 shown in FIG. % Was low. Therefore, it was confirmed that a high rate of single crystallization could be obtained by the method of this example.

FIG. 2 is a process diagram showing another embodiment of the method for growing a silicon single crystal according to the present invention. In FIG. 2, the same or corresponding parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. The silicon raw material rod 1 used in this embodiment is shown in FIG.
As shown in (a), a cone part 2 is preliminarily formed at one end as in the case of using a normal FZ method.

The cone portion 2 of the silicon raw material rod 1 is immersed in molten silicon 3 obtained by melting and melting polycrystalline silicon at a melting point temperature of silicon or higher to melt the cone portion 2 (FIG. 2 (b)). . Then, as in the CZ method, the silicon raw material rod 1 is gradually pulled up to recrystallize the cone portion 2 (FIG. 2C). The crystals of the cone portion 2 thus formed can have a large crystal grain length of 1 mm or more. It should be noted that the cone portion 2 may not be entirely recrystallized, and only the portion closer to the tip than the cross-sectional portion having a cross-sectional diameter of at least 60 mm may be immersed in the molten silicon 3 for re-crystallization. On the street.

Next, as described above, the silicon raw material rod 1 having the relatively large polycrystalline cone portion 2 having a long crystal grain is described.
Using, the silicon single crystal 8 is grown by applying the static magnetic field by the FZ method as in the first embodiment. A silicon single crystal having a single crystallization rate of 85% or more can also be obtained by the method of this embodiment.

[0030]

As described above, according to the present invention, it is possible to provide a silicon single crystal growth method capable of growing a silicon single crystal from a silicon raw material rod in one FZ step.

[Brief description of drawings]

FIG. 1 is a process chart showing an embodiment of a method for growing a silicon single crystal according to the present invention.

FIG. 2 is a process drawing showing another embodiment of the method for growing a silicon single crystal of the present invention.

FIG. 3 is a partial cross-sectional view showing a state of a melting zone 5 in the straight body portion of the silicon raw material rod 1.

FIG. 4 is a melting zone 5 in the cone portion of the silicon raw material rod 1.
It is a partial cross-sectional view showing the situation.

[Explanation of symbols]

 1 Silicon Raw Material Bar 2 Cone Part 3 Molten Silicon 4 Induction Heating Coil 5 Melting Zone 6,9 Solid-Liquid Interface 7 Crystal Grain 8 Silicon Single Crystal

Claims (3)

[Claims] 1. A FZ method in which a silicon raw material rod is partially heated and melted to form a molten zone, and the molten zone is moved from one end portion to the other end portion of the silicon raw material rod to grow a silicon single crystal. In the method for growing a silicon single crystal, one end of the silicon raw material rod is immersed in molten silicon to partially melt and then pulled up to form a conical recrystallized portion, and the recrystallized portion is used as a starting point. A method for growing a silicon single crystal, which comprises growing the silicon single crystal by the FZ method while applying a static magnetic field to the melting zone. 2. The method of growing a silicon single crystal according to claim 1, wherein the recrystallized portion is made of silicon polycrystal containing crystal grains having a length of 1 mm or more. 3. A cone-shaped portion is formed in advance at one end of the silicon raw material rod, and a portion of the cone-shaped portion having a cross-sectional diameter of at least 60 mm or more at the tip end side is immersed in the molten silicon. The method for growing a silicon single crystal according to claim 1 or 2, wherein the recrystallization portion is formed by pulling after melting.