A study of post exposure baking effect for CAR process in photomask fabrication

As the requirement of specification on photomask continues to be tightening with advanced logic and memory devices, the combined process of chemically amplified resist (CAR) and high acceleration voltage e-beam writing tool is widely used to meet the resolution and throughput for advance photomask fabrication. It is well known that the post exposure baking (PEB) condition makes serious effect on the characteristic of CAR due to its de-protection reaction with thermal acid catalyzation. In this paper, we present the PEB temperature effect on pattern resolution such as line edge roughness (LER) and proximity effect correction (PEC) latitude that is practical limitation in the combined process of 50 kV writing tool and CAR resist. Our results show that LER and PEC latitude are strongly dependent on PEB temperature due to resist contrast variation. At higher PEB temperature, increasing the contrast value can reduce the LER and it can increase the optimum PEC latitude.