Sticking effect on center-anchored circular plates in microstructures

In wet etching and cleaning processes of surface micromachining fabrications, a circular plate may adhere to its underlying substrate due to the capillary force of liquid. This paper studied the sticking effect between a center-anchored circular plate and its underlying substrate. Using the balance of capillary and elastic forces, we derived a critical gap for adhesion in terms of the parameters: gap between the plate and substrate, anchor radius, and outer radius of plate. This critical gap can be used to judge the potential sticking effect between the plate and substrate. Applying energy method, we derived another critical gap of adhesion, which determines the condition for releasing the circular plate from the underlying substrate by elastic force. Based on the two critical gaps, the sticking effect due to the plate thickness, surface tension of liquid, and two material properties: Young's modulus and Poisson's ratio is also discussed.