Complex 3D structures having lateral and depth resolutions of <1 µm and 20 nm, respectively, are fabricated in various polymers, including PMMA, ABS, CR-39, and others, by a direct photoablation process utilizing 172 nm radiation from flat microplasma-driven excimer lamps. The developed process does not require any toxic or photosensitive materials, and, therefore, may be performed outside of a clean room. The fabricated 3D structures may also serve as a master mold for PDMS and the curing of other materials.
Gratings, Fresnel lenses, phase masks, and waveguides are among the optical components that have been fabricated by 172 nm irradiation of various polymers through photomasks. Intensities above ~ 70 mW/cm^2 are now commercially available at 172 nm with flat Xe2 lamps. Such optical fluences are capable of precisely (< 500 nm lateral and 20 nm depth resolution) ablating a wide range of polymers, including PMMA and ABS, thereby allowing for a variety of 3D optical and biomedical components to be realized economically by dry processing.
Photolithographic techniques capable of producing sub-micron scale features typically involve laser or electron beam sources and chemical development of an exposed photoresist. We report here a novel, low cost photolithographic process utilizing flat, efficient lamps emitting at 172 nm. Recently developed 10 cm x 10 cm lamps, for example, produce more than 25 W of average power at 172 nm which enables the precise and fast patterning of most polymers, including those normally employed as e-beam resists and photoresists. Recent experiments demonstrate that PMMA films less than 100 nm in thickness are patterned in less than 20 s through a contact mask with high contrast resolution of 500 nm features. The ultimate resolution limit is expected to be ≤ 300 nm for a contact method. Electroplating technique was further used to deposit 500 nm gold features on a silicon substrate. The reported process does not require a photoresist development step and is performed in nitrogen atmosphere at atmospheric pressure which make it fast and affordable for fabrication facilities that have no access to high-tech photolithography equipment. Samples as large as 76 mm (3”) in diameter may be exposed with a single lamp in one step and areas of 1 m2 and above may be processed with tiled arrays of lamps.
Patterning of bulk polymers (acrylic sheets, for example) through a photomask and subsequent formation of sub-micron features has also been demonstrated.