Asymmetric biasing for subgrid pattern adjustment

The location of a printed edge can be controlled to a fineness that is two orders of magnitude smaller than the design grid, if a slight displacement of the pattern can be tolerated. The essence of this asymmetric subgrid biasing technique is the crenelation of two edges of a pattern into different periods. Fractional arithmetic results in a bias increment that much smaller than that can be achieved with halftone biasing. For a design grid of 20 nm (1X), and an exposure system with λ = 248 nm, NA = 0.68, and σ = 0.8, the bias increment can be as small as 0.22 nm. © 2001 SPIE · 1605-7422/01/$15.00.