A Study of Defects Due to Surface Processing in Silicon by Means of X-Ray Extinction Contrast Topography

Abstract

AbstractIn order to study the effects of processing variables on the defect contents of silicon wafers, an X-ray extinction contrast camera was designed and constructed to fit on the standard GE XRD-5 table. The camera, in its normal operating position, can be routinely used without interfering with the emission or diffraction instrumentation of the unit, and also can be mounted on the diffractometer stage for diffraction line breadth analysis. Routine laboratory procedures including sample preparation and mounting, film types, and film exposure and development are outlined.The correlation between extinction contrast topographs and optical photographs of sawed wafers is presented. Wafers were examined in the sawed, lapped, and chemically polished conditions. Subsequent to each processing step in the surface treatment of wafers, a series of topographs was made using four different crystal orientations. In this manner the three-dimensional picture of the defects is obtained, as are the Burger's vectors of all dislocations. It appears that internal defects such as dislocations are more uniformly distributed in lapped and chemically polished wafers than in sawed and chemically polished wafers. Furthermore, different doping impurities and levels cause different amounts of contrast in the dislocation images.