Optimization and simulation of exposure pattern for scanning laser lithography

Maskless optical lithography is a technique for writing patterns into an optically sensitive material (photoresist) without the use of a photomask. The patterning process involves exposing selected areas of the photoresist film to the sensitizing light to produce the desired pattern. Unfortunately, the exposure pattern required to produce the desired pattern (output) is not a simple function of the desired pattern due to the geometric properties and focusing limits of the optical beam. Thus, we seek a technique capable of generating an exposure pattern which will result in the desired pattern being transferred to the photoresist. This goal can be achieved by exploiting an inverse lithography technique (ILT) which has previously been used for mask design in micro-photolithography systems. The technique is carried out by interpreting process flow in terms of forward modelling and presenting a regularization term in a cost function of the optimization problem to approach an efficient solution. This reduction in computational complexity in parts of the optimization calculation, results in a much faster convergence than has been previously reported. Finally, the effectiveness of this method in terms of fidelity of the desired features and the time of the calculation are verified by computer simulation.