We study nonuniform transmission filters to improve resolution and/or depth of focus (DOF) in lithography. To understand the behavior of these filters for periodic structures we study the changes produced by the defocus in the image of a five-bar test. We analyze the behavior of the system with different degrees of coherence. For partially coherent illumination, we use the apparent transfer function (ATF), which is defined by the contrast in the image of a cosine grating object of the corresponding spatial frequencies. We also compare the ATF for incoherent illumination with the optical transfer function (OTF). © 1998 Society of Photo-Optical Instrumentation Engineers.
|Publication status||Published - 1 Apr 1998|
- Apparent transfer function
- Depth of focus