Structure Modification by Ion Bombardment during Deposition

It is shown that continuous or intermittent ion bombardment during deposition can change the growth mode of thick deposits formed by sputtering or evaporation. The columnar morphology commonly found when deposits exceed 1 μ in thickness can be disrupted and the deposit densified by negatively biasing the deposit and subjecting it to ion bombardment during growth. This effect is found to occur in a number of metal systems and may be attributed to resputtering during growth. In the case of sputter deposited tantalum, the density of 6-μ thick films can be increased from 14 g/cm3 at 0 deposit bias to 16.3 g/cm3 at −500-V bias. The macroscopic stress in the deposited film is also shown to be a function of the deposit bias. It is proposed that this growth habit modification may also be obtained in sputter deposited nonmetallic materials and chemical vapor deposits by ion bombarding the deposit during growth.