Large-area patterning of ∼50 nm structures on flexible substrates using near-field 193 nm radiation

Near-field contact exposures through a chromeless phase-shifting mask at 193 nm are used to create arbitrarily shaped structures as small as 45 nm on thin $\text{(∼10–15\hspace{0.17em}μ}\mathrm{m})$ sheets of polyimide. The thin sheets make smooth, stable laminates on carrier wafers through van der Waals interactions for processing like normal silicon wafers and can be removed to enable conformal mask contact during exposure. Further, the thin substrates are flexible enough to allow for curved and/or shaped photonic surfaces. When a silicon-containing bilayer resist is used, high aspect ratio $\text{(>4:1)}$ structures 50–80 nm in width are obtained following oxygen-plasma pattern transfer. Optical simulations using the finite-difference time-domain model are used to predict the near-field intensity distribution, and its results are compared to the experiments. This model indicates that with unpolarized light and a contact gap $\text{⩽25\hspace{0.17em}}\mathrm{nm},$ exposure latitudes in excess of 15% are possible for printing isolated, arbitrarily shaped features 50–60 nm wide over areas limited in size only by the mask dimensions $\text{(>10\hspace{0.17em}}\mathrm{cm}$ square).