Using low-contrast negative-tone PMMA at cryogenic temperatures for 3D electron beam lithography

Abstract

We report on a 3D electron beam lithography (EBL) technique using polymethyl methacrylate (PMMA) in the negative-tone regime as a resist. First, we briefly demonstrate 3D EBL at room temperature. Then we concentrate on cryogenic temperatures where PMMA exhibits a low contrast, which allows for straightforward patterning of 3D nano- and microstructures. However, conventional EBL patterning at cryogenic temperatures is found to cause severe damage to the microstructures. Through an extensive study of lithography parameters, exposure techniques, and processing steps we deduce a hypothesis for the cryogenic PMMA's structural evolution under electron beam irradiation that explains the damage. In accordance with this hypothesis, a two step lithography technique involving a wide-area pre-exposure dose slightly smaller than the onset dose is applied. It enables us to demonstrate a >95% process yield for the low-temperature fabrication of 3D microstructures.

CSAR 62 as negative-tone resist for high-contrast e-beam lithography at temperatures between 4 K and room temperature

“…Low-temperature negative-tone PMMA was found to suffer from an extensive swelling due to trapped gaseous scission products around 70 K that also reduced the etch selectivity in this temperature regime in a drastic way 11 . Low-temperature writing of PMMA also requires a two-step lithography technique to prevent it from peeling when trapped gases burst out 10,32 . In the case of CSAR 62 we did not observe such structural damage for structures written at low-temperatures, which makes it much more suitable for low temperature EBL.…”

“…Due to the emission properties of most semiconductor quantum dots, such processing has to be performed at low cryogenic temperatures or even liquid helium (l-He) temperature for sufficient signal-to-noise ratio 6 . Naturally, EBL is the most attractive technique to fabricate very precise or even three dimensional device structures with flexible design [7][8][9][10] . This initiates the quest for a detailed understanding of low-temperature-capable electron-beamsensitive resists 11 .…”

Quantitative mechanics of 3D printed nanopillars interacting with bacterial cells

“…An increasing number of advanced nanotechnological applications require highly repeatable fabrication of 'three-dimensional' devices with complex and precisely-controlled geometries. Depending on the targeted feature size and the complexity of the desired geometry, nanofabrication techniques, such as two-photon polymerization (TPP), 1 imprint lithography, [2][3][4][5] interference lithography, 6 3D molding, 7 electron beam lithography (EBL), [8][9][10] electron beam-induced deposition (EBID), [10][11][12][13] ion beam lithography (IBL), 14 or focused ion beam (FIB) 10,15,16 could be used to fabricate such 3D structures.…”

Parametric influences of fiber laser micro-machining for the generation of micro-channels on PMMA

“…In the present era, a rapid advance in micro-fluidic devices is observed owing to the need to perform large-scale applications. Micro-fluidic device fabrication was popularized by the conventional fabrication methods that include lithography [1], casting [2], injection molding [3], and hot embossing [4] on different traditional materials (silicon, glass, etc.) to various polymer materials.…”