Fabrication of 3D nanoimprint stamps with continuous reliefs using dose-modulated electron beam lithography and thermal reflow

Abstract

3D electron beam lithography and thermal reflow were combined to fabricate structures with multilevel and continuous profiles. New shapes, smooth surfaces and sharp corners were achieved. By using exposure with variable doses, up to 20 steps were fabricated in a 500 nm thick resist with a lateral resolution of 200 nm. Steps were reflowed into continuous slopes by thermal post-processing, and were transferred into silicon substrates by proportional plasma etching. The method can be used for the fabrication of 3D nanoimprint stamps with both sharp features and continuous profiles.

Light confinement effect of non-spherical nanoscale solid immersion lenses

“…17 Note that the T g of PMMA varies depending on the molecular weight M w , which also varies depending on the exposure dose of the electron beam. 17 Several studies report that reflow below 120°C led only to smoothing, the reduction of surface roughness, partial reflow, or partial deformation of the structures. [17][18][19] Therefore, we start with 120°C.…”

“…17 Several studies report that reflow below 120°C led only to smoothing, the reduction of surface roughness, partial reflow, or partial deformation of the structures. [17][18][19] Therefore, we start with 120°C. The reflow time is as well a governing parameter for proper reflow.…”

Optical characterization of subwavelength-scale solid immersion lenses

“…Since PMMA is a transparent thermoplastic, the thermal reflow structuring 14,15 can be applied and a final pattern can be directly used as an optical element in the visible spectrum. Recently, micro-size structuring by EBL and a following thermal reflow have been reported 16 . However, in order to achieve high-resolution nano-size patterns, one needs a very thin PMMA coating, which is typically below 500 nm.…”

“…Note that the T g of PMMA varies depending on the molecular weight M w , which also varies depending on the exposure dose of the electron beam 16 . Several studies report that reflow below 120°C led only to smoothing, the reduction of surface roughness, partial reflow, or partial deformation of the structures [16][17][18] . Therefore, we set our reference temperature to be 120°C.…”

Reflow of non-circular nano-pillars to fabricate nano-scale solid immersion lenses

“…As PMMA is also a thermoplastic, thermal reflow is applied to transform the flat-top pillar into a spherical structure. The glass transition temperature (T g ) of PMMA is approximately 110 ~ 120 °C, which mainly depends on the electron beam dose [7]. We heat samples above T g by using a hot plate.…”