Co-sputtering Superconducting NbTiN Ultra-thin Films On PSG/Si Substrates

NbTiN ultra-thin films on silicon substrates was studied in this paper. Due to high lattice mismatch between NbTiN and Si substrate will result in the difficulty to realize high superconducting properties. This work consists of two main parts: one is to rapidly prepare 250 nm thickness phosphorous doped SiO2(PSG) film on Si substrate by using a phosphorous diffusion process at low temperature. Second is to fabricate the high quality NbTiN film on PSG/Si by using a co-sputtering method. The results showed that it will take total 6 hours to prepare 250 nm PSG film on Si substrate, It is experimentally indicated that PSG/Si has similar phase and optical properties to Si O2/Si. With this optimized condition, the Tc of 5nm NbTiN/PSG/Si sample reaches 8.8K, which is 1K higher than that of 5nm NbTiN /Si sample, mainly due to a reduction of lattice mismatch between NbTiN and the silicon substrate and an improvement of interface property.This work provided some physical insight and technique approaches to grow high-quality NbTiN ultra-thin films on silicon substrates for the application of SSPD.