We show that accurate mass metrology can determine how dopants are added or material is removed during the plasma doping process. In case of erosion, information of mass reduction rate and selectivity can be obtained. Although deposition and erosion can occur simultaneous with implantation, a method is presented how to distinguish these basic reactions. Mass monitoring before and after anneal, reveals that As is very volatile. In the search for a solution we present a post treatment which reduces this loss, hence achieving lower sheet resistance.