Implementing chemically amplified resist to 10kV raster e-beam process in photomask manufacturing

Abstract

CAR(Chemically amplified resist) is widely used in 50keV VSB (Variable Shaped Beam) e-beam process in photomask manufacturing due to its advantage of high sensitivity which gives to reduced writing time compared to non-CAR. The 10kV raster e-beam system, however, is spread out already worldwide and plays a important role till now in middle grade mask-making. Conventionally the non-CAR like ZEP7000 has been applied to the 10kV raster e-beam system and it gives good performance for raster scan e-beam system. In mass production, sometimes, maintaining two kinds of resist simultaneously of CAR and non-CAR are inefficient strategy to the mask house which has limited resources. This situation makes the authors to apply CAR to the 10kV raster e-beam process. Generally, the grid of 10kV raster e-beam(MEBES) is large and limited compared to the current VSB grid. Historically, many layout data is designed already based on the large limited grid and this gives to limited sizing value. Moreover, it is difficult to control exposure dose in raster e-beam system and control bias with develop time in CAR process. These situations make more difficult CAR application to raster e-beam system under the simple mask data preparation strategy. In this paper, some critical problems will be discussed in isofocal process making for raster scan e-beam system. Advantage and disadvantage will be also discussed through the comparison of basic parameters such as dose margin, develop margin, and the fogging effect between the CAR and non-CAR process in 10kV raster e-beam process.