Stress analysis of silicon membranes with electroplated permalloy films using Raman scattering

We have measured the stress profile on a silicon membrane electroplated with a permalloy film using Raman scattering. The effect of silicon membrane thickness and permalloy film thickness on stress distribution was studied. Depending upon the nature of stress, the optic phonon in silicon at 520 cm^-1 either shifts upward (compressive) or downward (tensile). The phonon frequency shift is proportional to the magnitude of stress. A microscope X-Y stage was used to map the stress distribution over the silicon membrane that was covered and uncovered by the permalloy film. Silicon membranes in the thickness range, 9 μm < t_m < 12 μm, and permalloy films in the thickness range, 6 μm < t_p < 13 μm showed evidence of compressive stress. Based on the present results, membrane type microvalve design is optimized to prevent leakage, originating from stressed membranes. Such a nondestructive and noncontact microscopic stress analysis technique can be applied for design optimization in various magnetic MEMS devices.