Critical dimension issues for 200 mm electron projection masks

Electron projection lithography (EPL) is one possible successor to conventi onal optical lithography. One type of EPL mask, a SCALPEL mask, consists of an array of rectangular membranes on a 200 mm silicon support wafer. An im age of a die is formed by scanning and stitching the patterns resident on t he membrane array. Key areas of concern for controlling the mask critical d imension (CD) include temperature uniformity during the resist post exposur e bake (PEB) process, heating issues during resist exposure, fogging effect s caused by electron scattering from the mask chuck and variations resultin g from the pattern transfer of the mask scattering layer. A finite element model was used to evaluate heating issues during the mask writing step and PEB process. Masks were then written to verify the models. A Monte Carlo mo del was used to evaluate CD variations caused by electrons scattering from the chuck during the mask writing process.