Electrochemical method for defect delineation in thin-film SOI wafers

Summary form only given. An electrochemical method for the identification of defects and metal contamination in silicon wafers is discussed. This method is particularly suited for defect delineation in wafers synthesized for SOI. The procedure is applicable to (100) n-type Si with phosphorus dopant concentration of about 10¹⁵/cm³. Electrochemical etching is performed in 5-wt.% hydrofluoric acid utilizing a three-electrode configuration with the front side of the Si controlled at +3 to +5 V vs. a Cu/CuF₂ reference electrode. FTIR measurements of n^- epitaxial silicon on n⁺ substrate before and after electrochemical etching show that this procedure does not remove bulk Si. This property of the electrochemical etch makes it ideal for thin-film SOI wafers. Electron microscopy of etched wafers shows that the electrochemical etch produces crystallographic etch pits, 2 to 50 μm in size, formed in discrete regions of high electrochemical activity. Further, spreading resistance profiles indicate that dopant atoms are not selectively etched by this procedure. Electrochemical etch pits do correlate with both structural and impurity defects