Scanning thermal lithography: Maskless, submicron thermochemical patterning of photoresist by ultracompliant probes

This article introduces a scanning probe lithography technique in which ultracompliant thermal probes are used in the selective thermochemical patterning of commercially available photoresist. The micromachined single-probe and multiprobe arrays include a thin-film metal resistive heater and sensor sandwiched between two layers of polyimide. The low spring constant $(<0.1N∕m)$ and high thermal isolation provided by the polyimide shank is suitable for contact mode scanning across soft resists without force feedback control. The probes provide what is effectively a spatially localized postexposure bake that crosslinks the photoresist in the desired pattern, rendering it insoluble in developer. For $450-nm–1400-nm$-thick AZ5214E (Clariant Corp.), line and dot features with sizes of $450–1800nm$ can be printed using probe powers of $13.5–18mW$⁠, and durations of $1–60s$ per pixel. Variation of feature sizes with process parameters is described.