An apparatus has been constructed to analyze the particle flux of positive ions on surfaces from dry etching reactors. The particle flux can emerge from a great variety of reactive ion etching systems or from reactive ion beam etching sources. The particle beam passes through a small orifice with a diameter of 100 &mgr;m. A differentially pumped quadrupole mass spectrometer with a specially designed ion transfer optics performs the energy analysis of positive ions. The energy range can be varied between 0 and 500 eV with a resolution of 1%. The angular distribution measurements of the particle flux are carried out varying the inclination of the mass analyzer by ±20° with the vertex lying centrally in the sampling orifice. The angular resolution is about 1°. Rotation of the source on top of the apparatus and translation over ±10 cm inxydirection and 15 cm inzdirection perpendicular to it is provided in order to assure fully local resolution. The electrical properties of the orifice‐ion optics system is discussed with respect to their influence on ion trajectories. The purpose of the apparatus is to provide data on particle fluxes relevant for microelectronic processing.