Surface micro-structuring of glassy carbon for precision glass molding of diffractive optical elements

Karin Prater; Julia Dukwen; Toralf Scharf; Hans Peter Herzig; Andreas Hermerschmidt

doi:10.1117/12.2062904

25 September 2014 Surface micro-structuring of glassy carbon for precision glass molding of diffractive optical elements

Karin Prater, Julia Dukwen, Toralf Scharf, Hans Peter Herzig, Andreas Hermerschmidt

Author Affiliations +

Proceedings Volume 9192, Current Developments in Lens Design and Optical Engineering XV; 919211 (2014) https://doi.org/10.1117/12.2062904
Event: SPIE Optical Engineering + Applications, 2014, San Diego, California, United States

Abstract

Glassy carbon is used nowadays for a variety of applications because of its mechanical strength, thermal stability and non-sticking adhesion properties. This makes it also a suitable candidate as mold material for precision compression molding of low and high glass-transition temperature materials. To fabricate molds for diffractive optics a highresolution structuring technique is needed. We introduce a process that allows the micro-structuring of glassy carbon by reactive ion etching. Key parameters such as uniformity, surface roughness, edge definition and lateral resolution are discussed. They are the most relevant parameters for a stamp in optical applications. The use of titanium as a hard mask makes it possible to achieve a reasonable selectivity of 4:1, which has so far been one of the main problems in microstructuring of glassy carbon. We investigate the titanium surface structure with its 5-10 nm thick layer of TiO₂ grains and its influence on the shape of the hard mask. In our fabrication procedure we were able to realize optically flat diffractive structures with slope angles of more than 80° at typical feature sizes of 5 μm and at 700 nm depth. The fabricated glassy carbon molds were applied to thermal imprinting onto different glasses. Glassy carbon molds with 1 mm thickness were tested with binary optical structures. Our experiments show the suitability of glassy carbon as molds for cost efficient mass production with a high quality.

Citation Download Citation

Karin Prater, Julia Dukwen, Toralf Scharf, Hans Peter Herzig, and Andreas Hermerschmidt "Surface micro-structuring of glassy carbon for precision glass molding of diffractive optical elements", Proc. SPIE 9192, Current Developments in Lens Design and Optical Engineering XV, 919211 (25 September 2014); https://doi.org/10.1117/12.2062904

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