Effect of energetic neutralized noble gas ions on the structure of ion beam sputtered thin metal films

Abstract

Energetic ion bombardment of a sputtering target often results in a significant fraction of incident ions being reflected as energetic neutrals in the direction of the growing film. Experiments are described which test the degree to which bombardment by these energetic backscattered neutrals can influence the microstructure of a growing film. As anticipated, microstructural changes of the film are influenced by the reflection coefficient and energy exchange of a given energetic gas ion at the sputtering target which in turn depends on the mass ratio of the sputtering gas to that of the target. Whereas the sputtered metal species leave the target with a near cosine distribution, evidence for a strong noncosine reflection preference in the forward direction for the energetic backscattered neutrals will be given. Very careful x-ray diffraction studies show that films grown in a Ne/Pd system give rise to lattice dilation in the (111) lattice planes resulting in a 1% increase in the lattice parameter over Pd bulk values. On the other hand, in the Xe/Cu system no significant changes from bulk unit cell dimensions were observed. Data are also presented to show lattice distortions induced by deliberate energetic ion bombardment during film growth involving normalized energies much greater than that obtainable by energetic neturals. X-ray data show that lattice distortions and preferred crystallographic orientation induced by equivalent energetic particle bombardment differs significantly for different metals.