Wettability and reactivity of molten silicon with various substrates

Abstract

Contact angles of molten silicon on various substrates have been determined using the sessile drop method and reactivity has been investigated by examining cross sections between silicon and substrates with an electron-probe microanalyzer (EPMA). The contact angles between molten silicon and oxide substrates, such as SiO₂(s), Al₂O₃(s) and MgO(s), are in the range 85° to 88°. The reaction zone is composed of forsterite (2MgO·SiO₂) and clinoenstatite (2MgO·2SiO₂) on the MgO(s)-side of the interface between the Si and MgO. The contact angle between molten silicon and Si₃N₄ is about 90°. Molten silicon spreads over the SiC plate and the contact angle is estimated to be 8°. Large contact-angle values (around 145°) have been observed on BN substrates. At the interface between Si(l) and the BN substrate, a discontinuous Si₃N₄ layer is believed to form and might retard the dissolution of BN into molten silicon. The BN substrate is regarded as being the most suitable substrate for supporting a molten silicon drop during surface tension measurements, due to the large contact angle and low contamination.