A new apparatus for the controlled growth of single crystals by horizontal Bridgman techniques

Abstract

A unique apparatus for the growth of semiconductor crystals is described. This system can emulate the heat flow characteristics of the horizontal Bridgman-Stockbarger or gradient freeze crystal growth techniques without requiring motion of either the containment vessel, growth ampul or the furnace. The key features of the apparatus are the structure of the heating element subassemblies, the configuration of multiple element subassemblies into control zones, the use of dynamic heat flow balance to affect the radial and axial thermal profiles, and the use of dedicated microprocessors for process control and data acquisition. Thermal stability of ±0.1°C can be realized at temperatures in excess of 1275°C. Radial and axial temperature profiles may be readily altered. Temperature gradients may be varied up to 40°C/cm in the crystal, and up to 20°C/cm over the melt region. Radial asymmetry of up to 10°C across a 7.5 cm diameter bore may be obtained by control of external water cooling; the radial temperature profile is symmetric within ±0.5°C at 1000°C with balanced coolant flow. The capabilities of the apparatus have been assessed extensively. The system performance, modifications and critique of the operating features are presented.