STRUCTURAL-PROPERTIES OF A-SI-H RELATED TO ION ENERGY-DISTRIBUTIONS IN VHF SILANE DEPOSITION PLASMAS

We present measurements on typical silane-hydrogen RF/VHF deposition p lasmas and the corresponding a-Si:H films deposited from these plasmas . A range of process settings was used, covering both the alpha and th e gamma' regime of the discharge. Mass resolved ion energy distributio ns were measured at the grounded electrode to determine the ion flux a t the growing surface. Although the main precursors are radicals, in t he lower pressure alpha regime the flux of ions towards the surface ca n account for at least 10% of the observed growth rate. In the gamma' regime this contribution to the growth of the film is less. We measure d internal stress, hydrogen concentration, hydrogen bonding configurat ion, and refractive index to determine the effects of the ion bombardm ent on the structure of the deposited a-Si:H films. Good structural pr operties, i.e. a refractive index of about 4.25 at 600 nm and a minimu m number of SiH2 bonds, are found above a threshold energy of 5 eV per deposited atom. This observation is explained in terms of knock-on pr ocesses of the deposited atoms by ions and an increased mobility of th e growth precursors at the surface. Both these processes promote the f ormation of a dense film. (C) 1998 Elsevier Science B.V. All rights re served.