(751e) Tuning the Domain Size of Block Copolymers for Directed Self-Assembly Using Polymer Blending

Implementation of block copolymers (BCPs) in a directed self-assembly (DSA) scheme for industrial lithography introduces a series of scientific and engineering challenges that have not been significantly addressed in previous block copolymer phase separation studies. One fundamental engineering challenge that underlies the entire DSA field is the development of methods for producing large scale quantities of BCPs with low, controlled polydispersity and well controlled total and individual block molecular weights. Since the domain size D of a BCP is proportional to the degree of polymerization N, the pattern size and pitch of DSA patterns are strongly dependent on BCP molecular weight. In current optical photoresists, molecular weight variation in polymer batches mainly affects photospeed and is typically overcome using blending of polymer resins from different batches. Generally, this polymer blending in optical resists has relatively little effect on other resist performance characteristics such as CD control or line edge roughness (LER). In contrast, current DSA efforts are driving for the synthesis and use of extremely low polydispersity (i.e. PDI<1.1) polymers. This perceived need and demand for low PDI polymers for DSA processes is in direct conflict with such polymer blending strategies that could potentially be used mitigate polymer batch-to-batch variation and achieve tight matching of CD and pitch targets for DSA materials. Synthetic control of polymer molecular weight is still very challenging, and molecular weight variations of up to 10% are not uncommon in current DSA polymer synthesis. For reference, a 10% variation in molecular weight for a low PDI block copolymer used for DSA lithography would result in more than a 6% change in domain size. Therefore, there is a strong motivation and need to develop and understand methods for fine-tuning the domain size of DSA BCPs to meet the CD and pitch specifications that will be required for practical implementation of DSA processes.  This study investigates two methods of fine-tuning the domain size of a specific batch of BCP through blending of the BCP with another polymer, either 1. a set of similar homopolymers (HPs) or 2. a similar BCP of different molecular weight.  Each method was investigated and compared using a coarse grained molecular dynamics simulation.  For BCP-HP blends, the domain size increases as the amount of HP increases because the HPs tend to slightly swell the BCP domains.  For blends of different molecular weight BCPs, two different scaling regimes were identified; one regime is majority large chains and the other regime is majority small chains.  Using the simulation results, design heuristics were developed for both methods of blending which should guide experimental attempts to fine tune domain size.