MBMW exposure optimization for EUV mask stacks

Abstract

EUV Lithography makes substantial progress in optimizing (i) tool, (ii) mask blanks, and (iii) resist materials to support the next generation EUV imaging performance. Novel EUV masks use a variety of absorbers and capping layers fabricated on mirroring multilayer stacks coated on ULE substrate. 50 keV electron multi-beams are used to write high-resolution patterns in an appropriate resist coated over the absorber layer stack. The main goal of multi-beam mask writing (MBMW) has been the precise geometry control and faithful reproduction of the intended pattern on the substrate. \nThe highly conform MBMW resist-patterning process needs to understand the absorbed intensity distribution from the electron scattering in the resist/substrate stack, as well as the consecutive radiation-chemical effects induced by the electron energy spread together with the nonlinear dissolution behavior of the resist. It is difficult to exactly calculate the relative contribution of these factors separately, but their overall effect can be modeled by the analytic point spread response function (PSF) for the resist.\nThe ultimate resolution is determined by the amount of laterally- and back-scattered electrons from specific target compositions. These interaction events cause proximity, fogging, local heating, and surface charging effects, defining the accurate pattern. \nSimulations have shown alterations in the absorbed energy distributions of EUV masks with different stacks, and the experiments approved the results from the calculations. We present results of resist response to the electron multi-beam exposure based on statistical numerical simulation on different EUV-stacks directly compared with the corresponding numerical lithographic parameters extracted from the experimental resist screening. Consequently, all input parameters for MBMW writing corrections were precisely specified to the corresponding absorbed energy distribution signature of the concrete EUV mask.\nThe experiments were performed with the IMS MBMW-101 ALPHA tool in a high dose positive-tone chemically amplified resist (pCAR), provided by FUJIFILM, and coated on experimental EUV masks containing different novel stack compositions as prepared at HOYA Corporation.