Negative substrate bias induced modifications of the physical properties of DC sputter deposited nano-crystalline Mo thin films

Abstract

The negative bias on the substrate during DC sputter deposition of nano-crystalline molybdenum thin films has been utilized to tune their properties for solar cells and the cryogenic radiation detector applications. Films have been deposited on Si substrates under different out of plane negative biases aiming to improve their physical properties such as the sheet resistance, superconducting transition temperature, width of transition and surface roughness. Significant modifications in the electrical and surface morphological properties of nano-crystalline Mo thin films have been reported. The superconducting transition temperature and crystallite size of the films does not show much improvement but the surface roughness and electrical resistivity of the film have been improved by the application of substrate bias.

Studies on DC transport and terahertz conductivity of granular molybdenum thin films for microwave radiation detector applications

“…On the other hand, the sample Mo-B has roughly spherical grains with sharp boundaries and homogeneous distribution. Similar surface morphologies have been reported previously for the Mo films deposited using magnetron sputtering 23,[30][31][32] . The effect of impurities on the morphology and physical properties of Mo thin films has already been reported 33,34 .…”

“…The value of the RMS surface roughness is close to the roughness estimated from the XRR measurements presented above. The Mo films with similar small RMS surface roughness have been reported earlier as well 23,36 . The low surface roughness of Mo films is desirable for optical measurements as it reduces the diffused scattering from the surface asperities thereby allowing better THz transmission.…”

“…The thin film samples were deposited under the background argon pressure of 3.2 bar (Mo-A) and 3.4 bar (Mo-B) with the substrate kept at 75 mm from the target. The concentration of the residual impurity gases (primarily O2 and water vapor) and the rate of deposition have a large bearing on the morphology and electrical properties of the films 14,23 . Before the deposition of the Mo-A and Mo-B films, the system was allowed to be pumped only up to 2×10 -6 and 1.7×10 -6 mbar base pressures respectively.…”

“…The process can easily be scaled to deposit large surface area films and coatings useful for the industrial applications. We have previously reported the effect of argon pressure and negative substrate bias during film growth on the morphological as well as electrical properties of DC sputtered Mo films 14,23 . The rate of deposition and argon pressure during the deposition of the films can reproducibly tune the grain sizes and disorder in the films.…”