Photomask fabrication feasibility for next-generation reticle format

A next reticle format is considered from a view point of photomask fabrication process. In order to determine optimal reticle thickness corresponding to 230 mm size, processes feasibility for the thickness are examined. Cr dry etching is studied in terms of plasma condition and patterning accuracy. It is found that Cr dry etching with accurate critical dimension (CD) control is possible with substrate as thick as 12.7 mm. Post exposure bake (PEB) process for chemically amplified (CA) resists is also examined in terms of CD uniformity on substrates. Relationship of substrate thickness and CD uniformity is estimated with PEB controllability and CA resists characteristics. In addition to this, it is demonstrated that actual temperature uniformity for substrate with a thickness of 9 mm is equivalent to that for a present thickness of 6.35 mm. From these results in overall, it is proposed that substrate thickness of 9 mm is feasible for actual photomask production.