Effect of adatom mobility and substrate finish on film morphology and porosity: thin chromium film on hard disk

The morphology and porosity of thin chromium films are greatly influenced by the mobility of the adatoms on the growing film surface, which is controlled by substrate temperature, substrate bias during sputter deposition, and sputter pressure. Cr film of acicular morphology accompanied with higher film porosity is promoted at low substrate temperature; whereas increasing temperature will cause the growth of domed-top grain morphology with lower pinhole density. Energetic ion bombardment associated with substrate bias also leads to the formation of denser films. Another factor that has profound influence on the film porosity is the substrate finishing conditions. Films deposited on a substrate with random polishing scratches and plating pits are extremely porous and develop numerous pinholes. The pinhole density decreases when films are deposited on substrates with increasing stock removal during the subsequent texturing process. Therefore, smoother substrates also lead to reduced film porosity.