Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – For crystallization from liquid or supercritical state
Reexamination Certificate
2001-09-21
2003-10-14
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
For crystallization from liquid or supercritical state
C117S208000, C117S218000, C117S222000
Reexamination Certificate
active
06632280
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus for growing a single crystal used for production of single crystals such as silicon single crystals by the Czochralski method (also referred to as the “CZ method” or “pulling method” hereinafter), a production method and a single crystal.
BACKGROUND ART
Hereafter, conventional art relating to the present invention will be explained by exemplifying growing of a silicon single crystal.
An apparatus for growing a single crystal used for producing a silicon single crystal by the CZ method generally comprises a crucible accommodating a raw material melt, which can be moved upwardly and downwardly, and a heater disposed so as to surround the crucible, both of which are provided in a main chamber for growing a single crystal, and a pulling chamber for accommodating and taking out a grown single crystal is continuously provided above the main chamber. When a single crystal is produced by using such an apparatus for growing a single crystal, a seed crystal is immersed in the raw material melt and carefully pulled upwardly with rotation to grow a rod-like single crystal, while the crucible is moved upwardly according to the growth of the crystal so that the melt surface should be always maintained at a constant height in order to obtain desired crystal quality.
Further, when the single crystal is grown, the seed crystal attached to a seed holder is immersed in the raw material melt, and then the seed crystal is pulled upwardly with rotation in a desired direction by carefully winding up a wire by means of a pulling mechanism to grow a single crystal ingot at the end of the seed crystal. In this case, in order to eliminate dislocations produced when the seed crystal is brought into contact with the melt, the crystal in an early stage of the growth is once made thin to a small diameter of about 3 to 5 mm, and then the diameter is increased after the dislocation are eliminated so as to grow a single crystal ingot of desired quality.
At this time, the pulling rate for a portion having a constant diameter of the single crystal ingot is usually extremely slow, i.e., about 0.5 to 1 mm/min, and if it is pulled fast by constraint, there arisen problems, for example, the growing single crystal is deformed and thus a cylindrical product having a constant diameter can no longer be obtained, slip dislocations are generated in the single crystal ingot, the crystal is detached from the melt and thus it cannot be a product and so forth. Therefore, increase of the crystal growing rate is limited.
However, for the purpose of improving productivity and reducing cost in the production of single crystal ingots by the aforementioned CZ method, increase of the single crystal growth rate is one of considerable means, and various improvement have hitherto been made to achieve increase of the single crystal growth rate.
The pulling rate, i.e., the single crystal growth rate is determined by the heat balance of the growing crystal. The heat quantity incorporated into the crystal consists of inflow heat quantity from the melt and the heater and solidification latent heat generated when the melt crystallizes. When the heat balance of the growing crystal is considered, it is necessary that outflow heat quantity emitted out of the crystal from the crystal surface and the seed crystal should be equal to the sum of the inflow heat quantity and the solidification latent heat. The solidification latent heat depends on the volume of the crystal growing per unit time. Therefore, in order to increase the crystal growth rate, it is necessary to compensate increase of solidification latent heat provided by increase of the crystal growth rate by reducing the inflow heat quantity or increasing the outflow heat quantity.
Therefore, it is generally used a method of efficiently removing heat emitted from the crystal surface to increase the outflow heat quantity.
As one of such means, there was proposed apparatus in which the pulling rate is increased by providing cooling means in the main chamber so as to surround a single crystal ingot under pulling and thereby efficiently cooling the single crystal ingot under pulling. For example, there is the apparatus disclosed in Japanese Patent Laid-open (Kokai) Publication No. 6-211589. In this apparatus, a gas flow guide cooling cylinder having a double structure consisting of an outer cooling cylinder composed of metal and an inner cooling cylinder composed of graphite or the like is provided from the bottom portion of the pulling chamber to the inside of main chamber so as to concentrically surround a single crystal ingot under pulling and thereby heat generated in the inner cooling cylinder is transferred to the outside by the outer cooling cylinder, so that temperature increase of the inner cooling cylinder should be suppressed and cooling efficiency of the crystal should be improved.
Apparatuses utilizing cooling medium such as water in order to more efficiently cool a growing single crystal are also disclosed. For example, in the apparatus for growing a single crystal disclosed in Japanese Patent Laid-open (Kokai) Publication No. 8-239291, a cooling duct for circulating a liquid refrigerant is provided in a main chamber and a cooling member composed of a material having high heat conductivity such as silver is provided below the duct so as to rapidly transfer heat emitted from crystal surface to the outside and thereby attain effective cooling of crystal. However, if fluid such as water generally used as the cooling medium approaches the melt surface heated to a high temperature exceeding 1000° C., it may be a cause of phreatic explosion and thus dangerous. Therefore, in this apparatus, safety is secured by separating the cooling duct from the melt surface.
In these apparatuses, for example, in the aforementioned apparatus disclosed in Japanese Patent Laid-open (Kokai) Publication No. 6-211589, the outer cooling cylinder composed of metal and the inner cooling cylinder composed of graphite or the like in the double structure of the cooling cylinder show a difference in coefficient of thermal expansion and they are impossible to be always in perfect contact with each other. As for the disclosed apparatus, it is described that the diameter is made gradually smaller toward the downward direction so as to secure a larger contact area. However, even in such a case, they are actually contacted in a line and perfect contact cannot be obtained. Therefore, in an actual practice, a gap is formed between the outer cooling cylinder and the inner cooling cylinder and it acts as a heat insulating layer. Furthermore, there exists contact thermal resistance between the outer cooling cylinder and the inner cooling cylinder. This contact thermal resistance depends on type of material and surface condition, and it cannot be easily determined. However, in the structure used in the disclosed apparatus, the inner cooling cylinder cannot be cooled sufficiently and thus there is a problem that it is still impossible to exert significant crystal cooling effect.
On the other hand, as for the apparatus for growing a single crystal disclosed in Japanese Patent Laid-open (Kokai) Publication No. 8-239291, the cooling duct and the melt surface are separated and thus attention is paid for safety. However, in such a structure, the whole cooling duct is disposed at approximate center of the inside of the main chamber, and it causes problems concerning workability and operability in practical use. Further, it is difficult to secure sufficient strength of the duct due to its structure, and it is expected that the risk of leakage of liquid refrigerant due to breakage of the duct would increase.
Furthermore, there is an area between the cooling duct and the pulling chamber where the crystal is not sufficiently cooled. Therefore, the apparatus cannot always provide efficient removal of the outflow heat quantity emitted from the crystal, and it cannot be considered sufficient for obtaining significant cooling effect.
DISCLOSURE OF THE INVENTION
In view of the
Fusegawa Izumi
Hoshi Ryoji
Kitagawa Koji
Ohta Tomohiko
Hiteshew Felisa
Oliff & Berridg,e PLC
Shin-Etsu Handotai & Co., Ltd.
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