| Residual stresses in thin films are always a major concern in micromachining technology. The present work studies (1) behavior of residual stresses; (2) measurements of residual stresses; and (3) control and/or elimination of residual stresses.; In-situ observations of buckling evolution of a polysilicon microbearn during etch of its underneath sacrificial layer were carried out. As etching went on, the buckling pattern evolved from mode I, the sinusoidal half-waves, to mode H, the constrained sinusoidal half-waves, to mode III, the conventional mode, and finally to mode IV, the blister-like local buckling. Closed formulae were derived from theoretical analysis. The formulae predict buckling patterns if the residual stress in a microbearn is known. On the other hand, the residual stress in a microbeam can be evaluated using the formulae from the buckling pattern. The theoretical results agree with the experimental observations.; Micro-rotating-structures for local measurements of residual stresses in thin films were numerically simulated. A sensitivity factor was introduced and tabulated as a function of the structure parameters. Thereafter, a formula to calculate the residual stress is given and the residual stress can be easily evaluated from the rotating deflection. Residual stresses in both silicon nitride and polysilicon films were then determined using this technique and confirmed by the curvature method. As a result, micro-rotating-structures exhibited the ability to measure spatially and locally residual stresses in thin films with appropriate sensitivities.; Residual stresses and materials characterization of polysilicon thin films prior to and following rapid thermal annealing were studied. In comparison with conventional heat treatment, high-temperature rapid thermal annealing can reduce residual stress in a few seconds. The experimental results also suggest that residual-stress evolution during annealing is induced by two main factors: (i) change in grain size and (ii) nitridation at the top surface of the thin film. High-temperature annealing induces recrystallization of the polycrystalline films and promotes grain growth. The fact that the grain growth is much more pronounced in samples after conventional heat treatment implies that the surface nitridation dominates the final stage of residual stress during rapid thermal annealing. |
