Surface Analysis of Silicon Wafer

Recently the integration grade of LSI becomes higher and higher and much higher cleanliness of the surface of silicon wafer is demanded. The contamination on the silicon wafer surface is classified into two kinds, that is, impurity elements like heavy metals or alkaline metals and small particles. For the analysis of metallic impurity on the surface, vapor phase decomposition-atomic absorption spectroscopy (VPD-AAS) is effective, and the use of native oxide for the VPD is explained. The lower limits of detecion for total reflection X-ray fluoresscent (TRXF) and secondary ion mass spectrometry (SIMS) were determined with intentionally contaminated wafers. Observation of small particles on the surface of silicon wafer by using scanning electron microscope (SEM) is difficult because the particles are so small in size and number. A combined method of surface particle counter (SPC) and SEM is described. SPC is used to locate particle positions. The coordinates of each particle are then converted to SEM coordinates, and thus each particle is observed and analysed. Using this method, the time spent for the particle analysis on wafers is greatly reduced.