Ballistic and thermalized regimes to tune structure and conducting properties of W–Mo thin films

Abstract

W–Mo thin films are prepared by magnetron co-sputtering using glancing angle deposition. The same deposition angle αW = αMo = 80° is used for both W and Mo targets. Two different sputtering pressures are used: 0.33 Pa and 1.5 Pa, which correspond to ballistic and thermalized regimes of sputtered atoms, respectively. For each regime, W target current is kept at IW = 140 mA, whereas Mo target current gradually changes from IMo = 10–200 mA. Both regimes present porous thin films with inclined columns due to the shadowing effect that characterizes the films prepared with high oblique angle. Surface and cross-section morphologies exhibit elliptically bounded columns for the ballistic regime while they change to a cauliflower-like structure as thermalization prevails. At low pressure, the column angle β decreases with Mo target current and a Mo-enrichment of the films is noticed. Films are poorly crystallized at high pressure whatever the Mo target current with a high resistive behavior. The electrical resistivity vs. Mo content follows a rule of mixtures for films prepared at low pressure, whereas these deposited at high pressure correlate with a corrected Nordheim's law.