Transfer of photolithographic patterns by excimer laser ablation of polymers

Abstract

Pattern transfer of lithographically produced patterns is a key technology in microelectronics and other micro- and nanotechnologies. This approach has been perfected continuously to meet the requirements for size and quality, but vacuum processes are required for pattern transfer into microelectronic materials. Here an atmospheric pressure approach of pattern transfer by laser ablation is proposed and demonstrated. Similar plasma-based pattern transfer laser beams provide a directed energy impact to the exposed material, but the resulting material reactions are different as distinct primary processes govern the material removal mechanism by ablation. The laser ablation-based pattern transfer mechanism comprises (i) optical effects such as laser photon absorption and scattering processes, (ii) thermal processes such as material heating and melting, and (iii) laser ablation processes of the masking and the substrate materials. These characteristics cause topographical effects of laser-based pattern transfer (LiPT) process that results in a specific sidewall angle of the transferred pattern due to cone formation effects, trench formation related to diffraction and reflection at the patterns and surrounding wavy pattern due to laser beam diffraction. The ablation rate ratio determines the selectivity for laser-based pattern transfer and therewith the limit in depth. The pattern transfer can be achieved locally with varying parameters including different inclination angles. The results pave the way to a new approach for sustainable economic fabrication processes that do not need vacuum and reactive gases.