Role of impurities in zone melting recrystallization of 10 μm thick polycrystalline silicon films

Abstract

Zone melting recrystallization (ZMR) of polycrystalline silicon on SiO2 can offer an interesting, i.e., cheaper, alternative to the dielectric isolation technology used for high-voltage integrated circuits or smart power devices. For that purpose crystalline Si layers of 10–15 μm thickness are needed. In this work a mercury-arc lamp stripheater was used to recrystallize 10 μm thick polycrystalline silicon films. In unseeded layers, grain boundaries and subgrain boundaries appeared. By applying seeding, single crystalline areas of at least 1 mm by 1 mm were obtained. In these layers stacking faults were revealed as being the major crystal defect. In ZMR oxygen, nitrogen, and carbon are the major impurities which are incorporated into the silicon either intentionally or unintentionally. Among these impurities, nitrogen and carbon are believed to play a crucial role in promoting the wetting of the insulator and cap layer by liquid silicon. In this paper the distribution and transport of oxygen and nitrogen during ZMR are studied. It is shown that nitrogen can cause dendritic growth and that oxygen is unlikely to do so.