Photoresists with precisely controlled molecular weight, composition, and sequence

Abstract

One of the major challenges to lithography today is minimizing the consequences of stochastics, that is, the effect of statistical differences in photoresist structure and the distribution of additives, such as photo active compounds, in the photoresist. Most polymer photoresists due to their method of production will have large differences between polymer chains in molecular weight, composition, and sequence due to the nature of polymer synthesis. However, there exist methods of polymer formation that make uniform composition polymers such a homopolymers made using living polymerization. We discuss scissionable poly(phthalaldehyde)s as one example of a low stochastics photoresist. Using another method originally developed for the biological community we make polymers in which molecular weight, composition and sequence are identical in all polymer chains produced. Here we thus describe studies of polypeptoids, synthetic analogs of peptides, which have no chirality and in which the substituents are placed on the backbone nitrogen. The peptoids are produced as chemically amplified photoresists and are intended for study as EUV materials. To produce a CAR with aqueous base development using this hydrophilic backbone we have successfully learned how to make a more hydrophobic patterning system with Tg >100 °C. With our ability to control of sequence we have started to explore the effect that monomer placement has on lithographic performance and found that indeed sequence does play an important role. Sequences of solubility switch groups, adhesive, etch resistant and hydrophobic groups have been studied. Using e-beam lithography we have recently demonstrated sub-30 nm resolution.