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Fabrication of waveguide tapers by semitransparent mask photolithography

: Wengelink, J.; Engel, H.


Microelectronic engineering 30 (1996), No.1-4, pp.137-140
ISSN: 0167-9317
International Conference on Micro- and Nanofabrication (MNE) <1995, Aix-en-Provence>
Conference Paper, Journal Article
Fraunhofer HHI ()
masks; optical couplers; optical fabrication; optical losses; photolithography; fabrication; waveguide tapers; semitransparent mask photolithography; electron beam exposure; surface roughness; acetone; symmetric layer structure; fiber-chip coupling losses; fresnel correction; lateral alignment tolerances; relief structure; optoelectronic integrated circuits; 1.6 db

An improved process for semitransparent mask lithography is described. The uniformity of mask transmittance is increased by adapting the electron beam exposure field size to a binary multiple of the pattern period. In addition surface roughness of resist patterns is reduced by exposure of the resist-coated sample to an acetone atmosphere which results in negligible micro roughness. Using this process waveguide tapers employing a symmetric layer structure were fabricated. The tapers exhibit fiber-chip coupling losses of 1.6 dB after Fresnel correction and lateral alignment tolerances of +or-2.2 mu m for 1 dB excess loss. These values are comparable to results obtained for waveguide tapers fabricated using direct write electron beam lithography. This proves the described process to be suitable for the fabrication of relief type structures for optoelectronic integrated circuits.