Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Havin growth from molten state
Patent
1996-06-11
1998-10-06
Garrett, Felisa
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Havin growth from molten state
117 87, C30B 2962
Patent
active
058171738
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for making spherical crystals. In particular, the present invention relates to a method for making spherical crystals for use in semiconductors, dielectrics, magnetic bodies, and superconductors.
Spherical crystals can be made by growing crystals in a spherical form using the surface tension of a melt. Because of the symmetry in the outer shape due to the spherical structure, these spherical crystals allow easy creation of single crystals which have few defects and no disorder in atomic arrangement inside the crystals. In particular, an environment affected minimally by gravity will permit single crystals that are determined by the surface tension of the melt and are more spherical. Furthermore, since buoyancy does not affect the process, there is no thermal convection due to temperature differences, thus preventing disturbances. In cases where two or more elements are used to grow a crystal, segregation due to different specific gravities in the elements are avoided. Thus, it is possible to make spherical single crystals that have uniform composition and good crystallinity. These types of high-quality spherical crystals have many possibilities in industrial fields that use crystals. These spherical crystals can be used directly in applications such as electronic devices, optical elements, and functional elements.
Conventionally, single crystals for semiconductors and the like have been formed in the shape of rods, plates and films. Thus, the crystals have not been grown as spheres from the start. In particular, there have been no proposals at all for technologies that allow localized growth of spherical crystals on plate-shaped or rod-shaped crystal bases.
There have been three types of technology to grow single crystals for semiconductors: the method of using a melt to grow crystals; the method of growing crystals from a solute using a solvent; and the method of growing crystals through chemical deposition from the gas phase.
Generally, in the method of using a melt to grow crystals, the entire material is stored in a container such as a crucible or an ampoule. The material is heated and melted in an electric furnace that uses high-frequency heating or resistance heating. A seed crystal is put in contact with the melt, and it is pulled up while being rotated (the CZ method).
In the floating zone method (FZ method), a crucible is not used. This method is another popular method for growing single crystals. In this method for growing crystals, the melt forms melt zones between a rod-shaped seed crystal and a polycrystal. The melt is supported by surface tension while moving toward the polycrystals and are transformed into single crystals. However, forming stable floating zones in this method requires high surface tension and the use of material with low density.
In another method for growing single crystals, an electric furnace is not used, and instead a laser beam is used as a heat source. A material with a high melting point such as Spinel (MgAl.sub.2 O.sub.4) is melted, and the resulting melt is used to grow single crystals. Film crystals are obtained by melting amorphous silicon films on a silicon wafer. These techniques are well known. However, there is still no known method to directly create spherical single crystals by using heating beams such as laser beams to melt materials such as semiconductors, dielectrics, magnetic bodies, superconductors or metals.
There have been attempts made to grow semiconductor crystals and certain alloy crystals in microgravity environments. It has also been known that in microgravity conditions, melts have accidentally leaked to form spherical crystals. However, there have been no proposals for methods to intentionally grow spherical crystals. Furthermore, the idea of making spherical crystals by growing crystals spherically from a melt has not been proposed at all. The inventor of the present invention is focussing on the various possibilities for applying spherical crystals to electronic devices a
REFERENCES:
patent: 4099986 (1978-07-01), Diepers
patent: 5336360 (1994-08-01), Nordine
patent: 5431127 (1995-07-01), Stevens et al.
patent: 5544617 (1996-08-01), Terui et al.
patent: 5650007 (1997-07-01), Kawakami et al.
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