An improved method of doping a workpiece is disclosed. The method is particularly beneficial to the creation of interdigitated back contact (IBC) solar cells. A patterned implant is performed on one surface of the workpiece. A self-aligned masking process is then performed, which is achieved by exploiting the changes in surface properties caused by the patterned implant. The masking process includes applying a coating that preferentially adheres to the previously implanted regions. A blanket implant is then performed, which serves to implant the portions of the workpiece that are not covered by the coating. Thus, the blanket implant is actually a complementary implant, doping the regions that were not implanted by the first patterned implant. The coating is then optionally removed from the workpiece.