Understanding pattern collapse in photolithography process due to capillary forces.

Photolithography is the most widely used mass nanoproduction process. Technology requirements demand smaller nanodevices. However, smaller features risk collapse during the drying of rinse liquid because of capillary forces. In the present study, progress is made on two fronts: (i) The importance of surface tension force (STF) on three-phase line on the pattern collapse is investigated. The STF was ignored in previous pattern collapse studies. It is found that inclusion of STF increases the pattern deformation. The calculated deformation error from neglecting STF increases by increasing contact angle, pattern height to width ratio, and trough to width ratio. The deformation error decreases with an increase in elasticity module of pattern. (ii) A more accurate representation for the interface curvature (and related Laplace pressure), that is, using Surface Evolver (SE) simulation rather than cylindrical interface model (CIM), is presented. Curvature values of two-line parallel and box-shaped patterns are derived from SE and compared with the curvature values from CIM. It was found that CIM for the case of two-line parallel overestimates the curvature value and for the case of box-shaped underestimates it. SE simulations also showed that the error of calculating curvature values using CIM for both shapes is only a function of LAR (ratio of pattern length to trough width). For LAR values less than 20, the curvature values from CIM are not accurate for calculating pattern deformation.