Photomask blanks enhancement by optimizing resist baking and coating for advanced e-beam reticle fabrication

Advanced e-beam reticle fabrication, including phase-shifting mask (PSM) and optical proximity correction (OPC) reticle, has created a growing need for a resist system with wider process latitude, superior resolution and linearity, better CD uniformity. Some of aqueous-based DNQ-novolak resist systems, including chemical amplified one, have been proposed, however, their feasibility has not reached practical level yet. Accordingly, high-molecular polymer resist systems, conventional PBS for instance, are still the majors. We studied resist behavior to soft-baking conditions for the majors of high-molecular polymer resists in order to bring out their potential at its maximum. We also attempted to optimize coating thickness with an intention of superior linearity in conjunction with a risk of clear defects increase. We then examined very basic patterning features of each resist system in soft-baking latitude, coating thickness latitude, exposure dose latitude, develop latitude, adhesion and so on to make clear advantages and disadvantages of each the above resist system. This paper describes details of our findings on photomask blanks enhancement by optimizing soft-baking condition and coating thickness for the conventional high-molecular polymer resist systems for advanced e-beam reticle fabrication.