The role of defects in the diffusion and activation of impurities in ion implanted semiconductors

Abstract

Ion implantation is an extremely attractive method of selectively doping semiconductors, in part because the as-implanted distribution of impurities can be accurately predicted. However, electrical activation of implanted dopants generally requires high temperature annealing which allows these impurities to redistribute by various mechanisms. This paper reviews the role of defects in redistribution during the annealing of ion-implanted semiconductors. Some problems are inherent in the annealing process and are commonly observed in various materials. These include enhanced diffusion, gettering, and redistribution during recrystallization. Some problems are peculiar to compounds and include the effects of encapsulation, imbalances in crystal stoichiometry, and unequal recoil of host atoms of different masses. Dual implants and various implant temperatures have been employed in an effort to avoid some of these problems. Pulse annealing methods have also been investigated which reduce redistribution by considerably shortening the anneal time. However, problems associated with redistribution of dopants during annealing still limit the effectiveness of implantations in compound semiconductors.