The compressive stress transition in Al, V, Zr, Nb and W metal films sputtered at low working pressures

Abstract

Investigation of internal stresses in thin sputtered films of Al, V, Zr, Nb and W extends the observation of compression at low working pressures that was originally detected with Cr (D. W. Hoffman and J. A. Thornton, Thin Solid Films, 40 (1977) 355–363) and probes the atomic mass dependence of the transition pressure that was subsequently detected with Ti, Ni, Mo and Ta (J. A. Thornton and D. W. Hoffman, J. Vac. Sci. Technol., 14 (1977) 164–168). The observation of compressive stresses at sufficiently low sputtering pressures in all ten of the elements so far examined strongly supports the generality of this phenomenon. The five new metals under study also confirm the overall increase of the transition pressure with atomic mass indicated by the metals examined earlier. However, periodic deviations from the general trend are now evident among the group IVB, VB and VIB elements examined. The electrical conductivity and optical reflectance of the sputtered metal films exhibit abrupt changes in behavior near the transition pressure for compressive stresses. Above the transition pressure the conductivity and reflectance drop off rapidly; below the transition pressure these properties tend to level off at maximum values for the sputtered metal films. The interpretation of these observations in terms of a peening mechanism of energetic particle bombardment is discussed. Data are presented for films up to 0.3 μm thick sputtered onto glass substrates at a nominal deposition rate of 1 nm s −1 over the pressure range 0.067–4.0 Pa of argon.