Thin film block copolymer assembly in mixtures of highly selective solvents

Perpendicular orientation of block copolymer (BCP) domains in thin films is generally preferred over parallel orientation for lithographic applications. [1] Thermal annealing can be used to promote this orientation, but often requires a top coat since one block will typically wet the air interface. [2] Solvent annealing is an attractive alternative for achieving perpendicular orientation of the domains by neutralizing the surface energy of the air interface. Many examples of using solvent annealing in BCP thin films exist in the literature, involving domain non-selective [3] and selective [4] solvents. Silicon-containing polymers are desirable for lithographic applications because their high chi-parameters and high etch selectivity allow them to self-assemble into small domains and be transferred easily into an underlying substrate by oxygen etching. [5,6] This paper describes the process used to solvent anneal a new silicon-containing polymer, poly(trimethylsilyl styrene-b-lactide) (PTMSS-b-PLA) using cyclohexane vapor, a solvent that preferentially swells the PTMSS domain.