Increased oxygen precipitation in CZ silicon wafers covered by polysilicon

Abstract

Increased oxygen precipitation in CZ silicon wafers covered by a polysilicon layer has been observed after a high temperature anneal. This study established that the low temperature anneal, inherent in the LPCVD polysilicon deposition process, is so responsible for the enhanced oxygen precipitation effect. Temperature-time parameters were developed to match oxygen concentration in the wafer material with preannealing (polysilicon deposition) temperatures to achieve various degrees of oxygen precipitation. Data from this work show that interstitial oxygen reduction (δ Cox) saturation can be achieved after 100 min oxidation at 1150°C, if the polysilicon deposition temperature is between 670–700°C (150 min for a 1.3 Μm polysilicon layer) and the interstitial oxygen concentration in the wafer is between 22 and 24 ppm. A denuded zone of 20 Μm was obtained and can be observed on a chemically etched cross section. Chemically etched and decorated defects in these samples with various degrees of oxygen precipitation are also displayed in these optical micrographs.