157 nm resist materials: Progress report

Many semiconductor device manufacturers plan to make products with 157 nm lithography beginning in 2004. There is, at this time, no functional photoresist suitable for 157 nm exposure. Developing resist materials for 157 nm lithography is particularly challenging since water, oxygen, and even polyethylene are strongly absorbing at this wavelength. A modular approach to the design of a single layer resist for 157 nm has been undertaken. In this approach, the resist has been conceptually segmented into four functional modules: an acidic group, an acid labile protecting group, an etch resistant moiety, and a polymer backbone. Each of these modules has an assigned function and each must be transparent at 157 nm. Progress has been made toward finding candidate structures for each of these modules. We have demonstrated that acidic bistrifluoromethylcarbinols are very transparent at 157 nm and function efficiently in chemically amplified resists with both high and low activation energy protecting groups. Judicious incorporation of fluorine in acrylates and alicyclics has provided etch resistant polymers with greatly improved transparency at 157 nm. In particular, esters of poly(α-trifluromethylacrylic acid) are far more transparent than their protio analogs. The Diels–Alder adducts derived from reaction of these and other fluorinated alkenes with cyclopentadiene offer a route to a wide range of alicyclic monomers that show great promise as transparent, etch resistant platforms for the design of 157 nm resists. Polymers of this sort with absorbance below 2 per micrometer are reported.