Optically matched trilevel resist process for nanostructure fabrication

A novel trilevel resist process has been developed which enables high-contrast imaging of periodic structures with spatial periods down to 200 nm in thick resist on highly reflective substrates, using λ=351.1 nm argon-ion laser exposure. The process utilizes a 200-nm-thick, high-contrast, imaging resist layer, a thin (∼15-nm) evaporated dielectric interlayer, and a 300–600-nm-thick bottom antireflection coating (ARC) which suppresses reflections from the substrate. Our trilevel resist scheme has been implemented in a manufacturing process which utilizes a high-contrast interferometric lithography system for the formation of large-area, 200–1000 nm period grating and dot array images. The choice of interlayer is the most critical feature of this process. This material must have good deposition and adhesion properties, must be optically matched to the resist and ARC, must etch quickly during the reactive-ion etching (RIE) pattern transfer from the resist into the interlayer, must display very high selectivity to the ARC during the RIE pattern transfer into the bottom layer, and must be easily stripped after the trilevel resist structure has served its purpose. We also report on computer modeling which elucidates the factors influencing standing wave formation and present results of tests with several interlayer materials which display good optical matching and selectivities of up to 240:1 during RIE of the ARC.