FRAGMENTATIONAL COLLISIONS IN REACTIVE ION-BEAM PROCESSING

In a reactive ion beam etching (RIBE) system ion beams extracted from source plasmas by a two-grid optic with energies below 500 eV were analysed by energy selective quadrupole mass spectrometry (QMS). Both nonreactive plasmas (Ar) as well as reactive source plasmas with O2, SF6 and CF4 as feed gases were investigated at typical working pressures of 10(-2)-10(-1) Pa (10(-4)-10(-3) mbar) in the process chamber. At these conditions gas phase collisions of the ions with the background gas particles are likely to occur between the source and the substrate usually positioned at a distance of 20-30 cm from the grids during a process. For the generation of reactive and molecular ions, respectively, an ECR plasma source was used. From the energy distributions a strong indication of dissociative collisions in the process chamber was found as a significant phenomenon for a wide range of ionic species. Our results may be compared with mass and energy selective etch/deposition studies to discuss some aspects of gas phase fragmentation for the resulting surface properties.