Residual polishing damage and surface quality of commercial InP wafers: A scanning PL study

Abstract

The photoluminescence (PL) method has been used to investigate defects associated with surface polishing damage present in as-received commercial (100) LEC InP wafers. The wafers were chemically angle-polished to produce a surface bevel angle of ~ 0.01 ° using the method previously developed by Huber, but were not subsequently defect etched. For ‘as-polished’ wafers, total-light RT 2-D scanning PL images revealed on the bevel a ‘good’ zone extending to a depth of ~ 10 nm, a ‘damage’ zone extending from ~ 10 to ~ 70 nm, and an underlying ‘bulk’ zone. The defects in the damage zone appeared as irregular dark lines and patches of number density ~ 10 5 cm −2 and these were interpreted as arising from dislocations and mirco-cracks. The ‘bulk’ zone and unbevelled ‘surface’ zone showed no such damage defects. Defect etching produced shallow S-pits in the ‘damage’ zone, but not in the ‘bulk’ or ‘surface’ zones. Different ‘as-polished’ wafers showed differences in the amount and type of damage, while for ‘epi-ready’ wafers no damage zone was revealed. Possible reasons for the occurrence of ‘good’ and ‘damage’ zones in the PL images of the InP wafers are discussed. During the course of this work, PL results were also obtained from the surfaces of a range of as-received commercial InP wafers and InP epitaxial layers (un-bevelled). When examining a particular area, the background PL intensity often increased and then decreased as the laser beam irradiation time increased, the PL intensity sometimes changing by up to 5 x . The magnitude of the effect depended on the InP material and growth method and the power of the laser beam, and could be virtually eliminated by an initial low temperature anneal. Possible reasons for this effect and its significance are discussed.