Mid Sweden University

With resonator applications in mind, the residual stress in sputtered gold electrodes on quartz has been investigated with respect to varioiis deposition rates (2, 10, and 50 A/s), pressures (1.0 and 3 0- mbar), deposition temperatures (80OC and room temperature (RT)), film thicknesses (approx. 400 to 800 A), and substrate smoothnesses (lapped and polished), u:;ing the cantilever beam deflection method. Samples were monitored for 4 weeks at room temperature followed by 13 weeks of annealing at 85OC. The initial stress (ranging from -180 to -60 MPa) was compressive for all samples but turned tensile (a few megapascals) in some of the samples after annealing. A significant decrease in initial compressive stress appeared with samples coated at an elevated temperature. From samples preparecd at lower pressure and differing only in film thickness and substrate roughness, an increased compressive stress was found in thicker films and on rougher surfaces. The stress relaxation has been fitted to an exponential expression, and an attempt to relate the stress to a frequency shift (typically a few parts per million for ordinary, 100-pm thick AT blanks) has been made. With the help of transmission electron microscopy (TEM) the film morphology was investigated and related to the deposition parameters and aging. Judging from the increase in compressive stress and grain refinement with increased deposition rate and decreased pressure the atomic peening mechanism is the most likely reascm for the induced stress. Rutherford backscattering spectrometry (RBS) was employed to rule our the inclusion oj- argon (below or around 0.5%) as an explanation. From the vague, but clearly discernible, trend toward faster RT stress relaxation with higher initial stress, together with the liner film morphology, the relief mechaniism is believed to he stress-promoted grain boundary diffusion.