Resist planarization over topography using ion implantation

We present a novel application of ion implantation for obtaining planar films of resist on substrates with deep topography (≥1 μm). The motivation of this work comes from the fabrication of laterally coupled distributed feedback lasers, where lateral gratings need to be patterned adjacent to the sidewalls of a deep ridge waveguide. We demonstrate this process using both boron and phosphorous ion species implanted into polymethylmethacrylate (PMMA, 950 K) resist. The ion energies in our experiments ranged from a few tens of keV to approximately 1 MeV at a typical dose of 1013 cm−2. Experimental results show that the developed depth of the PMMA can be controlled very accurately. Furthermore, post‐implant x‐ray lithographic exposures show no deleterious effects of the implant on the PMMA characteristics. Lateral gratings (Λ=406 nm) were fabricated on 1.1‐μm‐high ridge waveguides in InP/InGaAlAs/InGaAsP by CH4/H2 reactive‐ion etching. This process is equally applicable for other applications where lithography...