A method and apparatus for doping a surface of a substrate with a dopant, with the dopant being for example phosphine or arsine. The doping is performed with a plasma formed primarily of an inert gas such as helium or argon, with a low concentration of the dopant. To provide conformal doping, preferably to form a monolayer of the dopant, the gas flow introduction location is switched during the doping process, with the gas mixture primarily introduced through a center top port in the process chamber during a first period of time followed by introduction of the gas mixture primarily through peripheral or edge injection ports for a second period of time, with the switching continuing in an alternating fashion as the plasma process.