Effect of process parameters on sidewall roughness in polymeric optical waveguides

Most polymeric optical devices are mainly fabricated by photolithography and reactive ion etching (RIE). This paper describes the fabrication of fluorinated polyether (FPE) waveguides by using a metallic hard mask and proximity exposure followed by RIE. In particular, we focused on the effects of various fabrication parameters on the sidewall roughness. According to our study, a high-power, low-pressure oxygen RF plasma environment will provide vertical and smooth sidewalls desired in a cladded waveguide. The sidewall roughness increases with pressure in pure oxygen plasma, while adding nitrogen gas to oxygen during RIE, creates a more vertical profile and smoother sidewalls along with low vertical and lateral etch rates. A simple technique is presented to quantify sidewall roughness using an atomic force microscope (AFM).