Measurements of the doping uniformity of ion-implanted silicon wafers

Ion implantation offers a degree of doping uniformity and reproducibility which is generally superior to that of conventional diffusion technology. On the basis of design considerations, most production-type implanters are capable of providing 2 sigma uniformity to better than 2 percent over 3 in. diameter wafers and repeatability of +-5 percent for the commonly used silicon dopants. This paper describes a technique which employs iso-sheet resistance topographs as a means of exhibiting the spatial distribution of impurities. Results are presented for electrostatic scanning and mechanical scanning implantation systems which demonstrate the importance of generic factors in limiting uniformity. 18 figures, 2 tables