Bridgman process - crystal growth, Prof. Dr. G. Dziuk, Freiberg University
Bridgman process - crystal growth, Prof. Dr. G. Dziuk, Freiberg University

Bridgman method - Bridgman furnace - silicon crystal growth

 

For the production of multicrystaline solar silicon the Bridgman method melts poly silicon in a high pressure furnace.  A crucible containing the silicon mold is moved form hot to cold in order to enable crystal growth.

 

The American physicist Percy Williams Bridgman has a great share in developing todays high pressure furnaces and contributed to crystallography, where he devised a method of growing single crystals. In 1946 he received the noble price for the invention of an apparatus to produce extremely high pressures, and for his discoveries within the field of high pressure physics.

 

The bridgman furnace works with three temperature zones. The upper zone with temperatures above the melting point of silicon. The lower zone with a temperature below melting point and an adiabatic zone as a baffel between the two.

The ampoule containg silicon is raised into the upper zone until only the lower portion of the single crystal seed remain unmelted in the lower zone. After the temperature stabilizes, the ampoule is lowered slowly into the lower zone to initiate crystal growth from the seed.

Due to a directed and controlled cooling process of the cast, zones of aligned crystal lattices are created.

Merely 60% of the polycrystal silicon can be processed to wafers for photovoltaics. The rest gets lost in the sawing and cutting process.