193-nm photoresists based on acid-catalyzed main chain scission

Abstract

Upcoming lithographic generations will suffer from new problems like line edge roughness (LER). For 248 nm a minor problem, LER becomes significant for lithography at higher resolution starting at 193 nm. So the concept of acid-catalyzed main chain scission of polymers for photoresist materials is expected to reduce LER occurring from phase separation phenomena of protected and deprotected polymers at the line edge and outgassing from the resist during exposure. To design new resist materials, we have studied imaging materials based on tertiary copolycarbonates that undergo the main-chain, acid-catalyzed thermolytic cleavage. The synthesis of copolycarbonates containing a tertiary diol structure has been achieved by using a solid-liquid phase-transfer-catalyzed polycondensation of the bis(carbonylimidazolide) of 2,5-dimethyl-2,5-hexanediol with various other diols in the presence of powdered potassium carbonate and 18-crown-6. The solubility and physical properties of the copolycarbonates are affected by the nature of the diol used in the polycondensation. We used 2,2-bis(4-hydroxycyclohexyl)-propane, tricyclo [5.2.1.0]-decanedimethanol, and DL-threitol as those diols to give the adhesion and dry etch-resistance properties into the backbone of the polymers suitable for 193-nm photoresists. The polymers synthesized are highly susceptible to thermal depolymerization and revert to small molecules when heated to temperatures which vary from 140-230 ℃ depending on the structure. The thermolysis temperatures are reduced well to below 100 ℃ if catalytic amounts of acid are added to the polycarbonates. Therefore the polycarbonates can be used to formulate highly sensitive resist materials with potential for self-development of positive images.