Coding gray-tone mask for refractive microlens fabrication

A new method has been developed to design gray-tone masks for microlens fab rication. Unlike previous methods which modulate the light intensity by cha nging the cell size or cell pitch only, the method relays on adjusting both the shape and position of a cell which gives an extra freedom to control t he design accuracy. Based on the theory of partial coherent light and the r esist development model, the intensity distribution through the gray-tone m ask and exposure of photoresist have been simulated. Nonlinear effects in a erial image and resist development have been take into account to correct t he mask design. A grey tone mask for microlens array has been fabricated an d printed by a g-line stepper. Hemispherical photoresist structures have be en achieved.