The Influence Of Sputter Gas Pressure On The Hardness And Modulus Of Tantalum Thin Films

Sputter deposited tantalum (Ta) thin films can form in 2 phases: the metastable tetragonal phase ([beta]-Ta) and the bulk bcc phase ([alpha]-Ta), both of which have wide applications. Producing Ta films with desired structure and properties is important, e.g. Ta films used for x-ray masks are required to have low stress; diffusion barriers between Cu and Si for semiconductors prefer [alpha]-Ta over [beta]-Ta. Varying sputter pressure while keeping other sputter parameters constant can be an effective way to tune both structure and properties of Ta films. It has been shown that, under good control of sputter parameters, we can get consistent variations in structure (stress, grain size) in [beta]-Ta films with increasing Ar gas pressure. This thesis shows that stress has little effect on [beta]-Ta indentation properties while variations in hardness can be well explained by the variation in grain size. All the metastable [beta]-Ta films transformed into [alpha]-Ta after thermally cycled to 700[MASCULINE ORDINAL INDICATOR]C. Nanoindentation results showed that both the hardness and indentation modulus are affected by the unique film structure of [alpha]-Ta films, which is characterized as having continuous orientation gradients and discontinuous grain boundary structure