Block copolymers will self-assemble when coated onto a patterned surface.
The trick is to pre-pattern the surface well enough so that the lowest energy state for the polymer is the desired accurate pattern. In this way, a less-than-perfect pre-pattern can become an excellent polymer pattern.
However, block copolymers can get stuck in mid-level energy ‘meta-stable’ states that have the wrong pattern (see diagram).
Researchers Juan de Pablo and Paul Nealey set out to find a way to encourage incorrect meta-stable states to climb their local energy barriers and drop into the correct pattern.
“What we have done in this work is predict the path these molecules must follow to find defect-free states and designed a process that delivers industry-standard nano-circuitry that can be scaled down to smaller densities without defects,” said de Pablo of the University of Chicago’s and Argonne’s Institute for Molecular Engineering.
Using the Mira and Fusion supercomputers, the team ran molecular simulations of self-assembling polymers and created algorithms to calculate where barriers to structural rearrangement would arise. Then they modelled how temperature, solvents and applied fields would affect the situations. The result was a way to predict the pathways of molecular rearrangement necessary to move from meta-stable to stable state.
Now de Pablo and Nealey are testing the theory at Belgian semiconductor lab IMEC, which has commercial-grade fabs and characterisation equipment.
Finding a defect in a 100cm2 area is like finding a needle in hay stack, and there are only a few places in the world where one has access to the necessary equipment to do so,” said de Pablo.
The work is described in ‘Molecular pathways for defect annihilation in directed self-assembly‘, a paper in the Proceedings of the National Academy of Sciences.