Effects of a thin SiO₂ layer on the formation of metal–silicon contacts

The reactions that occur between different metals and silicon wafers with a thin oxide layer have been investigated. The oxides were formed by either exposing the chemically cleaned wafer to air at room temperature or by thermally growing 30 Å of oxide at 700 °C in dry O₂. Al, Pt, and Au contacts were investigated. The interfacial reactions before and after heat treatment at 400 °C for 1 h were characterized using Auger and ESCA sputter profiling. The air grown oxides were found not to prevent intimate contact between the metal and the silicon, and reactions were observed for both heat treated and unheated samples. At 400 °C the 30 Å thermal oxide was found to be an effective diffusion barrier for Pt but less effective for Au. The Al reduced the 30 Å of SiO₂ to form Al₂O₃ at the interface in what appeared to be a self‐limiting reaction. A comparison between the reactions observed on air grown oxides and 30 Å of thermally grown oxide are consistent with observations that the room temperature oxides are not as fully formed as oxides grown at 700 °C.