The impact of thermal annealing and adhesion film thickness on the resistivity and the agglomeration behavior of titanium/platinum thin films

In this study, the influence of postdeposition annealings (PDA) up to temperatures of TPDA=900 °C on the room-temperature resistivity of e-beam evaporated titanium/platinum (Ti/Pt) bilayers on Si/SiO2 substrates is investigated. The thickness of the adhesion promoter is fixed to df,Ti=15 nm. In contrast, the Pt layer is varied between df,Pt=23 and 90 nm. In the “as deposited” state, an effective mean-free path for the electrons of 18 nm is extracted from the thickness-dependent electrical measurements, in reasonable agreement with theoretical predictions. Up to TPDA=450 °C, the dependence between the reciprocal platinum film thickness and the corresponding resistivity is linear, as expected from the size effect. At TPDA=450 °C, the resistivity is substantially increased independent of Pt film thickness. Due to an enhanced diffusion of titanium into the top layer the conductivity decreases preferentially at samples with df,Ti=15 nm compared to those with a lower adhesion promoter thickness of 5 or 10 nm. Above this annealing range, this effect is more pronounced, especially at a low platinum film thickness. In addition, thermal grooving effects occur which are more facilitated at higher TPDA levels and larger values for df,Ti. Upon annealing at TPDA≥1000 °C, the onset of a capillary-driven agglomeration process is detected. When applying a thicker adhesion promoter, a higher annealing level and/or a larger duration at TPDA is requested to complete the agglomeration process.