Growth of 40 mm diameter silicon crystals by a pedestal technique using electron beam heating

Abstract

Silicon crystals 40 mm in diameter were grown in vacuum from a 100 mm diameter polycrystalline pedestal rod using electron beam heating. The pedestal is consumed as crystal growth progresses, thus providing a continuous, crucibleless process. An eccentric placement of the annular electron beam impact ring on the pedestal melt is essential for process continuity and large diameter crystal growth. Crystals up to 0.9 m in length are grown by this process at growth rates in excess of 4.0 mm/min. The properties of these silicon crystals are similar to those of one-pass vacuum zoned crystals: dislocation density = 3 × 10 4/cm 2, lifetime > 50 μsec, oxygen and carbon content - none detected at 0.1 and 0.3 ppma detection limits respectively, radial resistivity variation < 10% for 30 ohm-cm, n-type doping. No tungsten contamination from the electron gun filament was seen at the 1.0 ppbw detection limit. Outstanding practical features of the pedestal method are the high crystal purity coupled with a relatively low material cost and fast crystal growth rate.