Depth-of-Focus Determination for Talbot Lithography of Large-Scale Free-Standing Periodic Features

The depth-of-focus (DOF) is an important factor to influence the pattern quality but seldom treated in conventional contact or proximity lithography. One explicit formula for DOF prediction is analytically derived in the context of photolithography of periodic features (i.e., the Talbot lithography), in which wavefront aberrations contributed by all diffraction orders are considered. Besides the numerical elucidations, a direct photolithographic process is also customized for experimental demonstration. With strict DOF estimation based on the governing equation for thickness control of the resist coating, large-scale freestanding features of micromeshes with well-controlled perforation and steepness are fabricated.