Masked ion-beam lithography: A feasibility demonstration for submicrometer device fabrication

Abstract

Masked ion-beam lithography (MIBL) is a high-resolution pattern-replication process that offers high throughput capability with submicrometer resolution. In MIBL, a collimated beam of protons is directed through a mask to expose a resist-covered wafer in proximity to the mask. We report here on four key MIBL technology issues: (1) mask technology, (2) radiation-damage effects, (3) resist materials, and (4) fabrication of NMOS devices using MIBL. We have established a process for fabricating thin (0.7 μm) silicon-membrane masks with submicrometer e-beam-generated gold absorber patterns. We have evaluated mask-induced beam scattering (<0.4° for channeled 175-keV-protons) and mask in-plane thermal distortions (<0.1 μm over 1 cm2 for 0.1 W/cm2 beam power) which are the principle factors affecting resolution and throughput. Radiation-damage effects were studied by simulating MIBL fabrication of MOS test chips. No statistically significant radiation effects were found after annealing at 450°C. We have demonstrated submicrometer resist patterning in both positive (PMMA) and negative (PS) resists, and have used these resists in the fabrication of submicrometer-gate NMOS test devices using MIBL exposures on all levels.