Scanning laser lithography is a maskless method for exposing photoresist during semiconductor manufacturing. In this method, the energy of a focused beam is controlled while scanning the beam or substrate. With a positive photoresist material, areas that receive an exposure dosage over the threshold energy are dissolved during development. The surface dosage is related to the exposure profile by a convolution and nonlinear function, so the optimal exposure profile is nontrivial. A gradient-based optimization method for determining an optimal exposure profile, given the desired pattern and models of the beam profile and photochemistry, is described. This approach is more numerically efficient than optimal barrier-function-based methods but provides near-identical results. This is demonstrated through simulation and experimental lithography.
This article describes two- and three-dimensional optical simulations for determining optimal conditions for near-field scanning optical lithography. It was found that a combination of 30-nm thick photoresist and 50-nm thick anti-reflective coating will yield optimal results with 405 nm incident light and a hollow-cantilever probe with 100-nm aperture width. In addition to identifying the optimal conditions, the sensitivity of the resolution with respect to each parameter is explored and plotted. The mechanisms behind each trend are described with supporting simulation data.