Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having moving solid-liquid-solid region
Patent
1996-10-29
1998-11-10
Kunemund, Robert
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having moving solid-liquid-solid region
117 3, 117900, 117915, 117 73, C30B 1500
Patent
active
058337482
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
This application is a national stage of PCT/DE95/00667 filed 12 May 1995 and is based upon German national application P4417105.6 of 16 May 1994 under the International Convention.
FIELD OF THE INVENTION
The invention relates to a method of obtaining fissure-free crystals in which the crystal is formed by a directional solidification from a melt in a quartz crucible and the crystal and crucible are at a temperature above about 300.degree. C. The invention relates also to an apparatus for carrying out the method.
BACKGROUND OF THE INVENTION
The semiconductive material gallium arsenide (GaAs) belongs to the group of III/V semiconductors and has by comparison with the classical semiconductor silicon, several interesting physical characteristics. These are, above all, the semi-insulating character of the GaAs, the direct band transition and the high mobility.
The economic significance of this material resides in the high potential for use in opto-electronics and high frequency technology which support the increasing demands of information handling systems.
Concrete uses in the form of LEDs, lasers, microwave diodes and solar cells usually use highly doped and thus conducting monocrystalline wafers.
An important precondition for an industrial use of the III/V semiconductor technology is the improvement of the III/V semiconductor technology by the improvement of GaAs substrate production and the increase in the reliability thereof so that, with respect to this goal, research in the field of crystal growth has been expanded.
At present the most widespread process in industry is the Czochralski process. Its use is based to a large measure on the significant involvement of this process in silicon crystal growth. With GaAs growth, however, other processes give better results. Crystals which are grown by the vertical Bridgman process (VB) have a reduced defect density by a factor of 10, whereby because of the potential automatabilty of this process it offers the possibility of low cost production.
The necessary conditions for carrying out the growth of the monocrystal by the VB process in a crucible are tied to the problem of contacting the melt with the crucible material. This contacting is avoided by the total liquid encapsulation so that the crystal grows quasi-crucible free. Quartz glass is used as a crucible material. The wetting liquid is boric oxide.
Crystals grown in a quartz crucible, apart from GaAs, include indium phosphate and others which have significant tendency to polygrowth and to twinning by comparison to crystals grown in pyrolytic boron nitride crucibles. The yield of monocrystalline GaAs can be sharply increased with this crucible material and thus the economics of the VB process can be increased.
The quartz crucible has, however, the drawback that the crystals form fissures during the cooling process upon the solidification of the boron oxide. These conditions result from the different thermal coefficients of expansion of the quartz glass and the GaAs. The fissures form in crystals which are initiated to a greater extent at temperatures below the 300.degree. C. boundary and occur in the softening zone of boric oxide known from the literature which extends from about 325.degree. C. until about the melt temperature (450.degree. C.).
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide a process which enables a fissure-free production of a drawn crystal.
It is also an object of the invention to provide an apparatus for carrying out the process.
SUMMARY OF THE INVENTION
These objects are attained in accordance with the invention in that a quartz crucible is immersed in a melt of a silicate-forming hydroxide compound which is at a temperature of about 450.degree. TO 600.degree. C. for its destruction.
It has been found that the destruction of the crucible enables fissure-free crystals to be obtained. This destruction must occur above the hardening point of the boron oxide and thus in the given temperature range.
As the hydr
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Althaus Martin
Kussel Eckhard
Sonnenberg Klaus
Defillo Evelyn
Dubno Herbert
Forschungszentrum Julich GmbH
Kunemund Robert
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