(236c) Poly(styrene)-b-Poly(acrylic acid) Block Copolymers: Phase Separation Behavior and Directed Self Assembly

Directed self-assembly (DSA) of block copolymers is a promising technology for extending the patterning capability of current lithographic exposure tools. For example, production of sub-40 nm pitch features using 193 nm exposure technologies is conceivably possible using DSA methods without relying on time consuming, challenging, and expensive multiple patterning schemes. Significant recent work has focused on demonstration of the ability to produce large areas of regular grating structures with low numbers of defects using phase separation-based self-assembly of poly(styrene)-b-poly(methyl methacrylate) copolymers (PS-b-PMMA). While these recent results are promising and have shown the ability to form patterns with pitches approaching 20 nm using DSA, the ability to advance to even smaller pitches will be dependent upon the ability to develop new block copolymers with higher χ values and the associated alignment and block removal processes required to achieve successful DSA with these new materials. This paper reports on work focused on identifying higher χ block copolymers and their associated DSA processes for sub-20 nm pitch patterning. Specifically, this paper will review our work focused on poly(styrene)-b-poly(acrylic acid) materials (PS-b-PAA).  We will review the synthesis and characterization of the block copolymers themselves, their phase separation behavior, and their performance in DSA.  It will be shown that poly(styrene)-b-poly(acrylic acid) copolymers (PS-b-PAA) are one promising material for achieving substantially smaller pitch patterns than those possible with PS-b-PMMA while still utilizing simple hydrocarbon polymers.  Characterization of the χ value for PS-b-PAA places it at approximately 0.18, which is roughly 4.5 times greater than the χ for PS-b-PMMA (χ_PS-b-PMMA ~ 0.04).  One particular advantage of PS-b-PAA polymers is that it is anticipated that much of the learning that has been done with the PS-b-PMMA system, such as development of highly selective plasma etch-based block removal procedures, can be directly leveraged or transferred to the PS-b-PAA system. This paper will specifically review the results of both solvent vapor annealing and thermal annealing processes and their differences in achieving DSA on topographic and chemoepitaxial guiding layers.