Process optimization and proximity effect correction for gray scale e-beam lithography

Three-dimensional microstructures find applications in diffractive optical elements, photonic elements, etc., and can be efficiently fabricated by e-beam lithography. Good process control and efficient proximity effect correction are important for achieving the desired structures. With polymethylmethacrylate as the resist, a process optimization of different develop conditions is carried out to identify a process that is most conductive to gray scale features. A novel proximity effect correction scheme called effective dose-depth (EDD) method is proposed. Using the EDD method for grating design and the optimized process, blazed gratings have been fabricated with excellent uniformity and low surface roughness.