Low pressure high frequency plasmas running on reactive gases are applied in industrial fabrication of microelectronic devices. Submicron pattern transfer into various layer materials is performed with a great variety of etching tools among which parallel plate diode and triode reactors or helicon sources as well as electron cyclotron resonance-, or inductively coupled plasma reactors are found. The etch rate, selectivity, anisotropy, and uniformity in these processes are a function of the flux characteristics of the particles impinging onto a surface to be structured. The ions and neutrals emerging from a plasma traverse the sheath in front of the substrate electrode. The electrical ac and dc fields across the sheath and the collision processes, the ions and neutrals are subjected to, define the mass selective angular energy distributions of these particles which in turn influence the profile developments. An apparatus is described, which is capable to simulate parallel plate diode reactors with the additional possibility to install various kinds of plasma or ion beam sources, in order to measure the flux characteristics of these sources. By this apparatus the mass selected energy distributions and angular distributions of particles emerging from the plasma sources are recorded with a quadrupole mass spectrometer equipped with an energy filter. For the measurements of angular distributions the quadrupole is tilted with the vertex lying in the center of a 100 µm orifice in the substrate electrode of a plasma reactor. The detected energies extend from 0eV up to the maximal energy defined by the potentials across the sheath and angular distributions with angular width of up to 15° full width at half maximum (FWHM) are identified. Both the energy distributions and the angular distributions are a result of charge transfer collisions, elastic scattering and dissociative collisions in the sheath in front of the substrate electrode. These distribution functions are consequently a result of the process parameters of an etch process and thus the detected distributions are used to interpret specific phenomena in submicron profile development.