The nature of defect layer formation for arsenic ion implantation

Abstract

A series of {100} silicon wafers were implanted with As ions over the range of 1×1013 at. cm−2 to 1×1016 at. cm−2 with energies of 50, 100, and 190 keV, using a commercial ion implanter, the Varian 200-DF4. Two end stations were used, the Waycool which provided good contact between the wafers and a thermal sink and the Wayflow, which holds the wafers without any provision for obtaining such contact. Precise values of amorphous layer depth were obtained by a newly developed technique, using direct measurement of the depth exposed by a tapered groove. For the Waycool implanted wafers, the amorphous layer depth increased with dose. For the Wayflow wafers, the amorphous layer depth increased to a maximum and then decreased, finally disappearing at the higher doses. Combining shallow angle-lapping, etching, and profilometry, it was possible to study the submerged amorphous layers originating at the threshold dose for the 190-keV implantations. For Waycool implanted wafers, the surface crystalline layer thickness decreased and disappeared with increased dose. For Wayflow wafers, the surface crystalline layer increased with dose, meeting the crystalline substrate which grew from the opposite direction. The differences in defect structure between Waycool and Wayflow implanted wafers are attributed to the dynamic annealing which occurs during implantation. The defects remaining after a low temperature transformation anneal are correlated to dynamic annealing effects.