The impact of using palladium gates for silicon quantum dot fabrication: defect densities and strain

Quantum dots (QD) in the silicon MOS system benefit from the use of palladium or platinum for gate materials because the small grain size of these metals compared to aluminum aids in shrinking the gate and dot dimensions. However, it is not clear what differences arise with respect to process-induced defect density and homogeneous strain. Here, we present measurements of oxide defect densities (fixed charge and interface trap density) as a function of forming gas anneal temperature for three different gate metals: Al, Ti/Pd, and Ti/Pt. We also investigate the concomitant effect of these anneals on the mechanical properties of the gate material, such as the intrinsic film stress, coefficient of thermal expansion, and bi-axial modulus. Our initial results indicate that Ti/Pd and Ti/Pt result in much higher fixed charge density and higher, though comparable, interface trap densities when compared to Al. These results provide guidance on adjusting QD fabrication for these gate materials.