Resist exposure optimization using figure of merit of resist profile

The resist pattern obtained after a lithography process must reproduce the features on the mask without any kind of distorsion. Best resolution obtained from a particular resist is limited by its contrast. A realistic resist image profile can be predicted using a detailed simulation program like SAMPLE. For characterizing resist image of small features, one has to take into account the abberations like corner rounding etc. This is not possible by the existing programs. Recently a method has been proposed for such an application using a figure of merit (FOM) concept. This approach has been used in this paper to optimize dose in a lithography process by simulation. Three dimensional resist image profile was first computed from a two dimensional image intensity distribution data, for a given rectangular object, by stimulating exposure and development process. Then resist image FOM is calculated from this resist profile. The effect of dose on resist FOM has been studied for different exposure wavelengths and feature sizes. From FOM Vs Dose curves one can get the optimum dose value, corresponding the maximum FOM value.