NONPARTICULATE ORIGINS OF LIGHT POINT-DEFECTS ON POLISHED SILICON-WAFERS

Numerous sources of nonparticulate light point defects (LPDs) not asso ciated with simple surface particle contamination on polished silicon wafers were identified and characterized. A direct relationship betwee n LPD counts and surface microroughness was established. The level of surface roughness strongly influenced the detection limit and density of LPDs detected by the laser scattering equipment. Etch pits observed on polished silicon wafers were also identified as LPD sources. Howev er, etch pits of 2 to 5 mu m diam were found to yield laser scattering cross sections equivalent to 0.1 to 0.5 mu m standard latex spheres, underestimating the actual size of the defect by an order of magnitude . Additional relationships between LPDs and crystal-originated defects were also uncovered. Density of LPDs strongly depended on the origina l wafer position in the ingot, implying a relationship between grown-i n defects and crystal-originated LPDs. Based on these findings, the im portance of nonparticulate sources of LPDs on polished silicon wafers and the need for further understanding of their formation mechanisms w ere clearly demonstrated.