The present disclosure provides a method to dope fins of a semiconductor device. The method includes forming a first doping film on a first fin and forming a second doping film on the second fin. The first and second doping films include a different dopant type (e.g., n-type and p-type). An anneal process is performed which drives a first dopant from the first doping film into the first fin and drives a second dopant from the second doping film into the second fin. In an embodiment, the first and second dopants are driven into the sidewall of the respective fin.