An approach is presented which allows to predict important characteristics of plasma based surface modification techniques like reactive ion etching (RIE), plasma etching (PE), ionized metal vapor deposition (IPVD), or plasma enhanced physical vapor deposition (PECVD). In a first step, the electrical field in the vicinity of the substrate is calculated by means of a self-consistent plasma boundary sheath model. In a second step, this field is used to calculate the energy and angular distribution of the ions impinging the surface. The knowledge of this distribution allows a more realistic prediction of essential process properties like the maximum aspect ratio of an etch process, or the obtainable conformality of a deposition step.