Effects of High Temperature Treatment on Curl and Microstructure of Heavily Boron Doped Silicon

An experimental study was performed to investigate the effects of high temperature treatment on the microstructure and curling behavior of heavily boron-doped silicon structures. Cantilever structures were created from p++ boron diffused silicon wafers. The post-diffusion high temperature 'anneal' treatment temperature was varied while the anneal time remained constant. The micromechanical cantilevers were analyzed for curl as a function of the anneal temperature using an optical profiler. Bulk sections from the wafers were analyzed to obtain boron concentration using secondary ion mass spectroscopy (SIMS) and to obtain the distribution of lattice constant using x-ray diffraction. Microstructure of plan-view and cross section samples was investigated with the transmission electron microscope (TEM). Results of the curl measurements revealed that all non-annealed cantilever structures were curled in one direction, and those annealed for 90 minutes above 1100 deg C were all curled in the other direction, with an apparent transition temperature of about 1050 deg C. SIMS analysis confirmed that boron concentration becomes more uniform through the wafer thickness with increasing anneal temperature. X-ray diffraction revealed that the magnitude of the smallest lattice constant present in a wafer increases with increasing anneal temperature. TEM observations showed that dislocation and precipitate density do not change with anneal temperature.Air Force Inst of Tech Wright-Patterson AFB OH is the author of 'Effects of High Temperature Treatment on Curl and Microstructure of Heavily Boron Doped Silicon', published 1997 under ISBN 9781423568087 and ISBN 1423568087.