Production device for high-quality silicon single crystals

Details Production device for high-quality silicon single crystals Production device for high-quality silicon single crystals

2001-11-20

2004-03-09

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Apparatus

For crystallization from liquid or supercritical state

C117S013000, C117S033000, C117S215000, C117S217000

Reexamination Certificate

active

06702892

ABSTRACT:

TECHNICAL FIELD
This invention relates to an apparatus for producing silicon single crystals for use as semiconducting material silicon wafers. More particularly, it relates to an apparatus by which high-quality, large-diameter, long-length silicon single crystals capable of giving wafers while reducing the occurrence of grown-in defects such as dislocation clusters and laser scattering tomography defects as far as possible can be produced and grown stably by the Czochralksi method (hereinafter referred to as “CZ method”).
BACKGROUND ART
The CZ method for pulling up and growing silicon single crystals is a method most widely used in the production of silicon single crystals for use in preparing semiconducting material silicon wafers.
The CZ method comprises dipping a seed crystal in molten silicon placed in a quartz crucible and pulling up the seed crystal to thereby allow a single crystal to grow. With the advancement in the technology of pulling up and growing silicon single crystals, it has now become possible to produce less defective, dislocation-free, large single crystals. Semiconductor devices are produced from wafers or substrates prepared from single crystals via several hundred processes. In the course thereof, the substrates are subjected to a large number of physical treatments, chemical treatments and, further, thermal treatments, including treatments in a severe thermal environment, such as high temperature treatments at 1,000° C. or above. Thus, problems are produced by microdefects, in particular grown-in defects, the causative factors of which have been introduced into single crystals in the process of their growth and which manifest themselves in some or other device production process and deteriorate the performance characteristics of the devices.
The distribution of typical ones among these microdefects is observed, for example, as shown in FIG.
1
. This is a schematic representation of the result of an observation of the distribution of microdefects, by X-ray topography, on a wafer sliced from a single crystal after growing, immersed in an aqueous solution of copper nitrate for deposition of copper and then subjected to heat treatment. This wafer shows, at a position about ½ of the outside diameter, oxidation-induced stacking faults (hereinafter referred to as “OSFs”). Inside this ring, there are found laser scattering tomography defects (also called “COPs” or “FPDs”, all being defects of the same kind resulting from deficiency of Si). Adjacent to and just outside the ring-forming OSFs, there is an oxygen precipitation promoted region, where oxide precipitates tend to appear. Further outside, in the peripheral region of the wafer, there occur dislocation clusters. These laser scattering tomography defects and dislocation clusters are called grown-in defects.
The sites of occurrence of the above defects are greatly influenced by the pulling rate on the occasion of single crystal growth. When a single crystal is grown while varying the pulling rate within the pulling rate range in which sound crystals can be obtained and when they are examined for the distributions of various defects in a plane cut longitudinally along the crystal center pulling axis, the results obtainable are as shown in FIG.
2
. As for the surfaces of disk-like wafers sliced perpendicularly to the pulling axis, an OSF ring first appears from the wafer periphery as the pulling rate decreases after shoulder formation and attaining of a desired single crystal diameter. The diameter of such OSF ring gradually decreases with the decrease in pulling rate and soon disappears, whereupon the whole wafer surface becomes one corresponding to the region outside the OSF ring. Thus,
FIG. 1
shows the sectional view at position A of the single crystal shown in
FIG. 2
, or the wafer surface from the single crystal grown at the pulling rate at that time. If the site of occurrence of the OSF ring is taken as a criterion, a higher pulling rate gives a high growth rate single crystal corresponding to the region inside the OSF ring and a slower pulling rate gives a low growth rate single crystal corresponding to the outside region.
It is well known that dislocations generated during single crystal growth and remaining in the wafer cause deteriorations in characteristics of devices formed thereon. OSFs increase the leak current and deteriorate other electric characteristics and the OSF ring is a result of high density occurrence of OSFs. Therefore, for use in ordinary LSI devices, the single crystal is grown at a relatively high pulling rate so that the ring-forming OSFs may be distributed on the outermost periphery of wafers or further outside the same. By doing so, the wafers can mostly consist of the region inside the OSF ring, namely a high growth rate single crystal, to thereby avoid dislocation clusters. This region inside the OSF ring is sometimes higher in gettering effect against heavy metal contamination which may occur more often in the process of device production as compared with the outside region.
With the recent increase in the degree of integration of LSI devices, the gate oxide films have become thinner and the treatment temperatures in the process of device production have become lower. Therefore, the occurrence of OSFs decreases and, owing to the decrease in oxygen content of crystals, ring-forming OSFs and other OSFs have been less problematized as factors deteriorating device characteristics. It has been revealed, however, that the occurrence of laser scattering tomography defects, which tend to be generated in high growth rate single crystals, greatly deteriorate the dielectric breakdown strength of gate oxide films, which are now thin. In particular when device patterns become finer, their influence is known to increase, making it difficult to increase the degree of integration.
Referring to the distribution of defects in the wafer shown in
FIG. 1
, there is a region, outside the OSF ring, in which dislocation clusters tend to occur. Between this OSF ring and the dislocation cluster occurrence region, there is a region adjacent to and just outside the OSF ring where oxide precipitation tends to occur, namely an oxygen precipitation promoted region, and, outside that region, there is a denuded zone where no dislocation clusters are detected. Inside the OSF ring, adjacent to the ring, there is also a narrow denuded zone where no laser scattering tomography defects can be detected.
If the denuded zone can be enlarged, there arises the possibility of wafers or single crystals very small in the number of defects being obtained. For example, Japanese Patent Application Laid-Open (Kokai) No. 08-330316 (1996) proposes a method of expanding only the denuded zone outside the OSF ring into the whole in-plane area of a single crystal without causing dislocation clusters to occur by controlling the temperature gradient within the crystal so that the value V/G (where V is the pulling rate (mm/min) during single crystal growth and G is the temperature gradient (° C./mm) within the crystal in the pulling axis direction in the temperature range between the melting point to 1,300° C.) may amount to 0.20 to 0.22 in the domain from the crystal center toward a position 30 mm from the periphery and, from that position toward the periphery, it may gradually increase.
In this case, it is indicated that the positions of the crucible and heater, the position of the semiconical thermal radiator made of carbon and disposed around the growing single crystal, the structure of the thermal insulator around the heater and other various conditions should be examined by global heat transfer calculations so that the above temperature conditions may be selected for the crystal growth.
Further, Japanese Patent Application Laid-Open No. 11-79889 (1999) discloses an invention concerning a production method which comprises pulling a single crystal in a manner such that the solid-liquid interface during the growth thereof may have a shape within ±5 mm relative to the mean position of the solid-liquid interf

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