(217be) Diblock Copolymer Directed Self-Assembly Line Roughness: Effects of Polydispersity and ?N

Directed self assembly (DSA) of block copolymers (BCPs), which relies on the use of surface features to guide the phase separation of the block copolymer into structures with long range order and precise registration, is a very promising technique for producing sub-30 nm pitch regular patterns. These patterns could be used as an enhancement to current lithographic techniques for manufacturing integrated circuit features below the current minimum pitch of ~80nm provided by leading edge 193nm lithography tools. One of the challenges in developing such DSA processes is understanding what the limits of such a process are in terms of defectivity, critical dimension control, and pattern roughness. A general goal of our work is to elucidate the connections between DSA material properties and process parameters and the characteristics of the resulting lithographic patterning achieved using such methods. In particular, this paper addresses two fundamental issues: (1) the connection between block copolymer polydispersity and pattern LER/LWR limits and (2) the connection between BCP χN value and pattern LER/LWR limits.

There is currently a drive to produce block copolymers for DSA with tightly specified molecular weights and extremely low polydispersities (i.e. polydispersity indices or PDI < 1.1). Such synthetic control of polymer molecular weight and PDI is extremely difficult and will make such materials expensive to produce. Furthermore, the perceived need for extremely low PDI materials is in conflict with the desire of material companies to be able to use polymer blending as a means to compensate for polymer batch-to-batch variation. In fact, such low PDI targets have been chosen somewhat arbitrarily without a fundamental understanding of the connection between BCP PDI and other DSA lithographic properties such as LER/LWR. In this work, we have used coarse grained molecular dynamics (MD) simulations of BCP DSA to study the effect of block copolymer PDI on DSA properties including LER/LWR and patterning capability. It is observed that as PDI increases from 1 to values of ~1.3, there is little effect on pattern LER/LWR, and as PDI increases above ~1.3 the LER/LWR increases slowly with increasing PDI. This suggests that LER/LWR concerns are not a major limitation in terms of determining BCP PDI specifications or the use of polymer blending methods.