Impact of sacrificial layer type on thin-film metal residual stress

In this paper we study the impact of two sacrificial layers on the final residual stress of thin gold films. In particular, we compare a typical photoresist layer (Shipley SC1827) to single-crystalline silicon. We fabricate and measure cantilever beams on both sacrificial layers and study their residual stresses by analyzing the final displacement profile of the released beams. All samples were fabricated at the same time and under identical conditions. The study clearly shows that the induced stress on thin films is dependent on the sacrificial layer. The gold film deposited over the single-crystalline silicon shows nearly zero gradient stress after release. On the other hand, gradient stress dominates the gold film deposited during the same run but over a photoresist layer. Such results are very useful in designing and fabricating a wide variety of low-stress actuators and sensors.