Abstract:
Optical simulation can be performed employing a calibrated printing model, in which a unique phase transmission value is assigned to each type of sub-resolution assist features (SRAFs). The printing model can be calibrated employing a mask including multiple test patterns. Each test pattern is defined by a combination of a main feature, at least one SRAF applied to the main feature, and the geometrical relationship between the main feature and the at least one SRAF. Generation of the phase transmission values for each SRAF can be performed by fitting a printing model employing phase shift values and/or transmission values for SRAFs with measured printed feature dimensions as a function of defocus and/or with measured SRAF printing behavior on a printed photoresist layer. A properly calibrated printing model can predict the printed feature dimensions, shift in the best focus, and presence or absence of printed SRAFs.