The use of plasma source ion implantation (PSII) for impurity sensitive substrates such as semiconductors has been slow to be adopted due to the difficulty of producing low impurity plasmas. In this work die feasibility of producing impurity-free plasmas for PSII using a mass filtering. technique is investigated. In this method, an ion cyclotron resonance (ICR) cell is incorporated into a plasma processing reactor to selectively expel unwanted ions. The implementation of ICR in ion implantation is subject to a number of complications, such as ion-neutral collisions, plasma shielding of excitation fields, and nonhomogeneities of die magnetic field. A numerical simulation of ICR-based mass filtering for PSII to investigate these effects has been developed. Mass filtering is potentially effective over a wide range of magnetic field configurations at the pressures typically used for PSII.