Fabrication of low loss polyimide optical waveguides using thin-film multichip module process technology

Polyimides containing fluorine are attractive for integrated optics since the introduction of fluorine increases the optical transparency in the visible and near infrared spectrum. Polyimides are easily integrated with silicon or GaAs optical devices, can be spin-coated on a number of substrates and are resistant to chemical etchants, solvents and package assembly temperatures. Photosensitive polyimides are being widely used as dielectrics in multichip module fabrication because they offer a combination of good electrical and mechanical properties and low cost processing relative to non-photosensitive polyimides. In this paper, a simple, wet chemical patterning process for the fabrication of low loss waveguides using photosensitive polyimides is described. Optically transparent, fluorinated polyimides are modified by copolymerizing a low concentration of photocrosslinking groups into the backbone. The polyimides can then be patterned into channel, ribs, or Y branches by UV exposure through a photomask followed by wet chemical development. Sidewall smoothness and sidewall profiles can be controlled by varying exposure and development conditions