(236e) Fundamentals of Diblock Copolymer Phase Separation and Directed Self-Assembly Processes: Detailed Analysis of Lamellae Formation
Directed self assembly (DSA) of block copolymers, which relies on the use of surface features to guide the phase separation of a 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. In order to speed the development of such techniques and to understand the behavior and limitations of such processes, computer simulation of such methods are proving invaluable. In this work, the number of atoms required to simulate a useful size of polymer during the DSA process has been reduced by coarse graining the atomistic polymer into a mesoscale model form based on Kuhn segment beads to represent the polymer chain. Such mesoscale models have been developed and carefully parameterized to reproduce the behavior of potentially useful DSA block copolymers (e.g. PS-b-PMMA). These mesoscale models have been implemented into MD simulations using GPU-based computing based on a modified form of the HOOMD-Blue software package. These simulations have been used to probe several interesting questions related to block copolymer phase separation and DSA processes. First, the scaling of the pitch of phase separated patterns with the polymer degree of polymerization and chi value will be analyzed. This scaling is an important issue for those designing polymers to achieve selected target pitches for integrated circuit manufacturing. Comparisons of simulation results to a large amount of experimentally determined pitch data which indicate that the simulations are able to quantitatively predict and explain the observed behavior quite well will be shown. While it is commonly known that the order-disorder transition (ODT) in bulk diblock copolymer phase separation occurs at a XN value of ~10.4, the nature of the effective ODT in DSA processes utilizing thin diblock polymer films on topographical or chemical guiding substrate layers is not well understood. This paper will discuss the concept of an effective ODT for such thin film DSA processes and will show how this ODT depends on a a variety of factors including film thickness, nature of the guiding layer, and diblock copolymer properties. Finally, the effect of diblock copolymer polydispersity on the ODT and the resulting pattern quality (e.g. edge roughness behavior) will be discussed.