Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – For crystallization from liquid or supercritical state
Patent
1995-11-27
1998-03-24
Breneman, R. Bruce
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
For crystallization from liquid or supercritical state
117 13, 117208, 117218, C30B 3500
Patent
active
057307997
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device and a process for producing single crystals of silicon (and similar materials) having little contamination or thermal oxidation induced stacking faults, thus enabling the production of wafers whose gate oxide films have excellent dielectric strength. This device and process are also suited for finely controlling the oxygen content of the pulled crystal.
BACKGROUND ART
Single crystals that are produced in according to the Czochralski process contain appreciable amount of oxygen, which has been melted out of the quartz (SiO.sub.2) crucible, as the silicon melt reacts with the quartz crucible. consequently, during repetitive heat treatment which occurs in the IC and LSI manufacturing processes, this oxygen tends to prevent the occurrence of slips and burrs. Furthermore, during the heat treatments at a temperature of approximately 1000.degree. C., oxide precipitates in the crystal aggregate to form stacking faults of high density and reduce the impurities in the surface layers of wafers cut from the crystal (a phenomenon known as intrinsic gettering).
FIG. 6 schematically illustrates a cross section of a current device and the pulling-process according to the Czochralski technique. The crucible 1 is comprised of a quartz vessel 1a on the inside and a graphite vessel 1b on the outside. A heating element 2 is mounted outside the crucible 1, in which the melt 5, the charge material for the crystal melted by the heating element, is contained. A seed crystal 3 is lowered until it makes contact with the surface of the melt 5 and then is pulled upward to grow a crystal at its lower end. These parts and components are contained in a metallic vessel provided with a water cooling device, all of which constitutes a whole device for producing single crystals.
During the course of the single crystal pulling process, inert gas (such as argon gas) of high purity is introduced into the metallic vessel 6 from above at the center, forming a gas flow 30. The gas flow 30 turns into a gas flow 31 containing both silicon monoxide (SiO) that has evaporated from the surface of the silicon melt 5 and carbon monoxide (CO) generated as a result of the silicon monoxide reacting at high temperatures with the graphite components such as the heating element 2, the graphite vessel 1b, etc. The gas flow 31 flows down along the outside and the inside of the heating element 2 to be discharged through the discharge ports 8.
Since the argon gas flow 31 in the metallic vessel 6 is turbulent and locally stagnant, silicon monoxide is deposited on the ceiling of the vessel 6 layer by layer or in particle forms. Fine particles or small blocks of the deposited silicon monoxide fall onto the surface of the melt 5, are incorporated in the boundary layer of the growing crystal and give rise to dislocations in crystal.
Another problem is that, the silicon melt is contaminated also, unless carbon monoxide is properly discharged. That is, the carbon monoxide incorporates into the single crystal, will induce lattice defects in the single crystal.
In order to effectively obviate these problems, two devices mentioned below has been proposed.
FIG. 4 illustrates schematically a pulling assembly (the first device) proposed by the U.S. Pat. No. 4,330,362: Kokoku No. 57-40119. This device is characterized by having an upper flat annular rim 7a projecting beyond the crucible edge and a joining piece 7b attached to this annular rim 7a and extending downwardly and cortically from its inner edge, the joining piece 7b being 0.2 to 1.2 times as high as the crucible 1.
FIG. 5. illustrates schematically another pulling assembly (the second device) disclosed in Kokai No. 64-72984. This device is characterized by having a heat resistant and heat insulating cylinder 10 that extends downward coaxially surrounding the single crystal 4 being pulled and is tightly joined to the subvessel 6c at its junction with the metallic vessel 6. The device is also characterized by having a heat resistant and heat insulating annular
REFERENCES:
patent: 5004519 (1991-04-01), Hariri
patent: 5264189 (1993-11-01), Yamashita et al.
patent: 5363796 (1994-11-01), Kobayashi et al.
patent: 5441014 (1995-08-01), Tomioka et al.
patent: 5450814 (1995-09-01), Shimishi et al.
patent: 5476065 (1995-12-01), Ikezawa et al.
Breneman R. Bruce
Garrett Felisa
Sumitomo Sitix Corporation
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