Abstract
Applications for high resolution 3D profiles, so-called grayscale lithography, exist in diverse fields such as optics, nanofluidics and tribology. All of them require the fabrication of patterns with reliable absolute patterning depth independent of the substrate location and target materials. Here we present a complete patterning and pattern-transfer solution based on thermal scanning probe lithography (t-SPL) and dry etching. We demonstrate the fabrication of 3D profiles in silicon and silicon oxide with nanometer scale accuracy of absolute depth levels. An accuracy of less than 1nm standard deviation in t-SPL is achieved by providing an accurate physical model of the writing process to a model-based implementation of a closed-loop lithography process. For transfering the pattern to a target substrate we optimized the etch process and demonstrate linear amplification of grayscale patterns into silicon and silicon oxide with amplification ratios of ∼6 and ∼1, respectively. The performance of the entire process is demonstrated by manufacturing photonic molecules of desired interaction strength. Excellent agreement of fabricated and simulated structures has been achieved.
Highlights
Device performance can frequently be significantly improved by moving from the typically 2D fabricated structure to a 3D geometry, for example in the case of plasmonic nanostructures[1] or multi-gate FET transistors[2]
In thermal scanning probe lithography (t-SPL), a heated scanning probe is used to locally remove the resist polyphthalaldehyde, which decomposes endothermically when it comes into contact with a hot tip
Are fabricated in a single patterning run with high resolution[17] rather than requiring one patterning run per depth level[16]
Summary
The written amplitude falls to half the target amplitude for a half wavelength of λc = 48 nm for Fig. 3g This lateral resolution is consistent with the finite opening angle slope of the t-SPL tip and the patterning depth. We have developed a complete resist-patterning and pattern-transfer solution that provides high resolution lateral and nanometer-accurate vertical fabrication of grayscale patterns in a substrate To achieve this goal, we have implemented a closed-loop lithography process that is capable of fabricating surface profiles in resist with an accuracy of less than 1 nm in a single pass. We anticipate that the ability to fabricate 3D topographies with nanometer accuracy will open up new routes for the experimental realization of nanoscale devices as well as for exciting fundamental studies in fields ranging from tribology to electron optics
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