JPS5914434B2 - Manufacturing equipment for band-shaped silicon crystals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for manufacturing band-shaped silicon crystals.

As shown in FIG. 1, the band-shaped silicon crystal 11 is formed by a seed crystal (not shown) from the tip of a capillary die 13 (13a, 13b), which is a nozzle-like structure vertically erected in the silicon melt 12. is used to pull it up with a cross section that follows the shape of the hole at the tip of the die 13.

Numeral 14 is a crucible containing a silicon melt, which is heated from the outside to keep the silicon in a melt state.

When pulling a band-shaped silicon crystal, the intermediate gap in the die 13 plays the role of a capillary tube and supplies melt to the tip of the die 13.

In order for the intermediate gap to have such a function, the die 13 must be made of a material that has the physical property of being "wettable" by the silicon melt 12.

This is the first characteristic required of the material of the die 13.

The second characteristic required of the die 13 is that it be strong without being corroded or deformed even when used in contact with the silicon melt 12.

Unfortunately, to date, no die material has been discovered that fully meets these two requirements.

That is, materials with good wettability are attacked by silicon melt, and conversely, materials that are strong against silicon melt have poor wetting properties.

Currently, dies used to pull silicon band crystals are made of high-density molded carbon.

Although high-density molded carbon satisfies the first requirement, it is insufficient for the second requirement. Carbon dissolves in the silicon melt, and as a result, silicon is present in the pulled crystal band. Carbide is mixed in, and this is one of the causes of degrading the properties of the crystal.

The present invention has been developed in view of these drawbacks, and has improved the structure of the carbon capillary die currently used for pulling band-shaped crystals to prevent silicon carbide from being mixed into the band-shaped crystals. The present invention provides an apparatus for manufacturing band-shaped silicon crystals.

Before describing the features of the present invention in detail, the mechanism of silicon carbide mixing into band-shaped silicon crystals will be explained.

Silicon carbide is a crystal with a diameter of about 10 pm, and when a band-shaped crystal is dissolved in a mixed solution of hydrofluoric acid and nitric acid, it has a size that can be recognized with the naked eye as a residue.

In order to investigate the route by which silicon carbide of this size gets mixed in, the inventor cut the die after it had been used for pulling a band-shaped crystal and polished it with a mirror, and found that there was almost no silicon carbide outside the die. Silicon carbide was present in the form of crystal growth on the wall surface of the intermediate cavity.

The size of the crystal grains was almost the same as that observed in band-shaped crystals.

Based on this fact, the inventor concluded that the silicon carbide mixed in the band-like crystals is a result of crystal growth on the wall surface of the intermediate cavity of the die, which flakes off at some opportunity and is incorporated.

Next, the inventors investigated the cause of silicon carbide crystal growth in the capillary-die intermediate gap.
A thermocouple covered with a quartz tube was inserted into the die cavity to measure the temperature.

As a result, the temperature of the silicon melt in the intermediate gap was the lowest at the upper end, and increased toward the bottom.

Based on this fact, the inventor discovered that carbon dissolves in the silicon melt, and as the melt passes through the intermediate gap and rises, the solubility of carbon decreases as the temperature decreases, and it is no longer completely dissolved. It is concluded that carbon is precipitated in the form of crystals on the walls of the intermediate cavity in the form of silicon carbide.

Since the mechanism by which silicon carbide is mixed into the crystal is as described above, this can be avoided by creating a capillary die in which the temperature does not drop in the intermediate cavity.

Based on the above considerations, the capillary die of the present invention has a rising path for the silicon melt only at the side end, and the silicon melt rising through this rising path is horizontal to the crystal growth region at the tip. It is configured to be supplied in the direction.

As a result, silicon carbide is precipitated only in the ascending path of the silicon melt where a temperature gradient is formed in the vertical direction at the end of the die, and is not precipitated in the crystal growth region where there is no temperature gradient in the vertical direction. Crystals are obtained.

FIG. 2 shows the main structure of an embodiment of the present invention.

What is different from FIG. 1 is the capillary die 21 (21a).

21b).

That is, in the die 21, a void is formed only in the peripheral portion outside the broken line in FIG. 2a, and there is no void in the central portion.

A rising path Al is provided at both ends of the die 21 to vertically raise the silicon melt to the die tip position as shown by arrows.
7 A2 is formed.

As the silicon melt cools along this ascending path A11-A2, silicon carbide is deposited on the die wall surface.

However, there is no belt-shaped crystal growth position above this melt rising path A17A2, and the rising melt changes its path in the horizontal direction as shown by the arrow and is supplied to the crystal growth region B.

In this crystal growth region B, there is no temperature drop of the melt, and therefore no silicon carbide is deposited on the goo wall surface.

At both ends of the crystal growth region B, there are stoppers 2 for the surface flow of the melt.
20 and 222 are provided.

As a result, when the silicon carbide generated by the vertical melt flow flakes off from the goo wall surface and floats to the melt surface, it is moved by the movement of the melt into the crystal growth area B.
It prevents it from reaching .

As a result of the inventor pulling a band-shaped silicon crystal using a die made of high-density molded carbon having the shape described above, silicon carbide, which conventionally existed at approximately one point per 1 d of band-shaped crystal, was reduced to virtually zero. , even those rarely found were small in size, less than 10 μm.

In addition, the grain size of the individual microcrystals constituting the band-shaped crystals has increased, and less harmful twin grain boundaries have come to occupy most of the grains.

Furthermore, the surface irregularities of the band-shaped crystals have been reduced to several tens of micrometers or less compared to the conventional method, and the number of crystal pulling failures has been significantly reduced.

This is because the silicon carbide was not caught by the rollers that drive the strip crystal in the vertical direction, and the pulling was smooth.

As explained above, according to the present invention, the structure of the carbon capillary die is improved, silicon carbide is prevented from being mixed into the band-shaped silicon crystal, and high-quality band-shaped silicon crystal can be obtained.

[Brief explanation of drawings]

1A and 1B are a front view and a side view conceptually explaining a conventional band-shaped silicon crystal production apparatus, and FIGS. 2A and 2B are conceptually explaining the main structure of an embodiment of the present invention. They are a front view and a side view. 11... Band-shaped silicon crystal, 12...
Silicon melt, 2H21a, 21b)... Capillary die, A11 A2... Melt rising path, B... Crystal growth region, 22°, 22□...
...Stopper.

Claims (1)

[Claims] 1. A carbon capillary die is placed in a crucible containing a silicon melt, a seed crystal is brought into contact with the silicon melt rising to the tip of the capillary die, and the seed crystal is pulled up. In the apparatus for producing a band-shaped silicon crystal, the capillary die has a rising path for the silicon melt only at the side end, and the silicon melt rising through this rising path reaches the crystal growth region at the tip. 1. An apparatus for producing a band-shaped silicon crystal, characterized in that it is configured to be supplied in a horizontal direction. 2. The device for producing a band-shaped silicon crystal according to claim 1, which has stoppers at both ends of the crystal growth region at the tip of the capillary gouer to prevent surface flow of the silicon melt.