Formation of a silicate layer between lead oxide and a silicon-wafer surface during heat treatment

Abstract

PbO thin films were deposited on a silicon substrate by plasma-enhanced chemical vapour deposition (PECVD) using Pb(C2H5)(4) and oxygen at 250 degrees C. The interdiffusion reaction phenomena between the PbO thin film and the silicon substrate during heat treatments were investigated in a horizontal furnace in the temperature range between 350 and 650 degrees C under a nitrogen ambient for 1 h. The PECVD PbO film deposited on the silicon substrate at 250 degrees C, was amorphous and contained carbon-related contaminants which could almost be removed by heat treatment at 350 degrees C. The PbO on the silicon substrate initially participated in the interdiffusion reaction in the temperature range between 400 and 450 degrees C. This produced a silicate layer containing lead components. The lead content in the film varied with the depth of film and heat-treatment temperature. Metallic lead was observed as a cluster in the specimen heated at 550 degrees C. This cluster was produced by the agglomeration of metallic lead originating from PbO decomposition. The oxygen source for silicate formation was not ambient oxygen coming from the decomposition of Pb-O bonding. The metallic lead clusters dissolved as weakly bound metallic lead or as an unbound nanosized metal particle in the silicate layer at 650 degrees C.