Impact of thermal and structural effects on EUV lithographic performance

Thermal and structural effects will be an important consideration for all advanced lithography approaches targeting the 100nm technology generation and beyond. Such effects can contribute to loss of CD control, decrease in process latitude and reticle-wafer overlay error, This necessitates a system approach to account for thermo-mechanical effects in a complete system performance analysis of an EW lithography tool. Multilayer-coated mirrors will typically absorb 35-40% of the in-band radiation causing thermal deformation of the mirror figure. In addition, Mo-Si multilayer films are deposited with compressive stress of approximately 350 MPa, which will also serve to deform the mirror substrate. To study these effects, we have inter-connected the capabilities of several software packages which include thermal and structural finite element, optical, and lithographic analysis. This enables us to determine the impact of mechanical effects on Lithographic metrics such as the exposure-defocus process window, pattern placement and throughput. This paper includes results from a theoretical study of an EW alpha tool with a wafer throughput of 20 200mm wafers per hour (assuming 80% die coverage and 68% exposure time) for the 100nm technology generation.