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Thin films residual stress profile evaluation using test microstructures: Illustrated on an example of AlN film

In this study, we investigate the residual stress gradient of aluminum nitride thin film deposited by reactive pulse DC magnetron sputtering technique on a 200 mm diameter silicon wafer with a 1 μm layer of plasma enhanced chemical vapor deposition tetraethylorthosilicate. Stress measurements are obtained using in situ fabricated rotational beam microstructures. The rotating beam moves in response to relief of the residual stress on the connecting arms that experience lengthening or shortening due to compressive or tensile residual stresses, respectively. Various arm-beam connecting joints, separation gaps between the arms, and arm lengths are considered to determine the optimum microstructure for localized residual stress evaluation of the sputtered aluminum nitride. The displacement of the rotating beams with four different arm-beam connecting-joint designs is analytically modeled using COMSOL multiphysics finite element method simulation. The results of the analytical model were found to be in agreement with the results observed through experiments. The stress gradient measurements obtained using the microstructures are compared to the Stoney stress evaluated using a wafer bow technique. Although the predicted Stoney stress shows a 220 MPa tensile residual stress, the observed trend in localized stress values shows that the maximum stress is 280 MPa at the center of the wafer and reduces to about 100 MPa at the edge of the wafer.