Analysis and optimization of multilayer silver superlenses for near-field optical lithography

An analytical method based on transmission matrices is used to study the imaging performance of multilayer silver superlenses for near-field optical lithography. The spatial-frequency transfer functions of these systems show complex structure, and the best lens stack to use depends upon the feature sizes to be imaged, the distance from the final silver surface and the image plane, and the required level of transmission of the lens stack. The balance between the DC and the fundamental spatial-frequency component in the transfer function is also crucial in determining the quality of the final image that is formed. Graded-thickness lens stacks are introduced and analyzed for the first time, and it is shown that these systems can have a flat transfer function over a wide range of spatial frequencies, which may make them more versatile for practical systems.