Post-nucleation phenomena in the Volmer-Weber mode of epitaxy

Two commonly used methods of depositing a thin film in vacuum are evaporation and sputtering. Evaporation has the advantage of rapid deposition in relatively high vacuum for non-refractory materials. Evaporated films are, however, liable to be weakly bonded to the substrate, because of the low arrival energy of the evaporant, unless effects such as chemical bonding occur. Sputtered films generally bond strongly but sputtering is a much slower deposition process than evaporation so that there may be a high density of contaminating inclusions. As charging also affects the sputtering process special techniques such as r.f. sputtering must be employed for insulating targets.A saddle-field ion source has been developed which operates with cold cathodes and without a magnetic field at pressures compatible with evaporation. Evaporated films deposited in the presence of a beam from this source exhibit the bonding properties of sputtered films. The beam contains a high proportion of energetic neutrals so that the method can be applied to both insulating and conducting substrates. The ion source is compact and can be installed generally in existing vacuum equipment. The source geometry can be varied to ensure that the area covered by the beam matches the deposition area.