The Effect of Photoresist Outgassing on Boron Clustering and Diffusion in Low Energy BF2+ Ion Implantation

Abstract

ABSTRACTDuring high current ion implantation into photoresist-covered substrates, evolution of gaseous by-products of photoresist breakdown occurs that can affect the dose control of the process as well as diffusion and activation of the implanted dopants in silicon. The dosimetry effects are well understood and accounted for in modern ion implanter design. In this work, we report on the effect of photoresist outgassing on the distribution of boron concentration in silicon during the subsequent annealing process, boron electrical activation and sheet resistance measurements. Experiments were performed on mono- crystalline and pre-amorphized silicon and oxide covered wafers that help elucidate the mechanism of boron accumulation and diffusion. Higher carbon concentration on the wafer surface due to photoresist outgassing results in boron clustering and reduction of transient enhanced diffusion, leading to higher sheet resistance at low anneal temperature. Implantation through a thin oxide layer can be used to reduce carbon surface contamination and minimize the effects on the boron profiles and sheet resistance.