Multi-beam mask writer exposure optimization for EUV mask stacks

Background: EUV lithography is making substantial progress in optimizing (i) tool, (ii) mask blanks, and (iii) resist materials to support the next generation EUV imaging performance. EUV masks use a variety of absorbers and capping layers fabricated on mirroring multi-layer (ML) stacks. Aim: The highly conformal e-beam resist-patterning process needs to understand the absorbed intensity distribution spread 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 dissolution behavior of the resist. Approach: We present the results of resist response to 50-keV electron multi-beam exposure based on statistical numerical simulation on different EUV absorbers and reflecting ML stacks directly compared with the numerical lithographic parameters extracted from the experimental resist screening. The experiments were performed with the IMS Nanofabrication Multi-Beam Mask Writer (MBMW) ALPHA tool in a positive Chemically Amplified Resist provided by FUJIFILM, coated on experimental EUV masks with different stack compositions prepared by HOYA. Results: All input parameters for MBMW corrections were precisely specified to the corresponding absorbed energy distribution signature of the specific EUV stack. Experiments confirmed the necessity to match the model calibration values to each small change in the mask stack composition. Conclusions: The method was successfully implemented into leading-edge mask writing and resist/substrate/tool testing for achieving the sub-7-nm node at different EUV-mask stacks.