Effects of aberration and flareon lithographic performance of SFET

摘要

The effects of aberration and flare on the lithographic performance of the EUV small-field exposure tool (SFET)were evaluated. Simulation results indicated that the effect of aberration on the image contrast of line-and-space (L&S)patterns should be small. In exposure experiments, 26-45-nm L&S patterns were successfully fabricated under annularillumination (σ=0.3/0.7). A key factor limiting resolution should be resist performance. Simulation results also indicatedthat the astigmatic aberration could produce a focal shift of about 60 nm between horizontal and vertical L&S patterns.The experimentally obtained focus shift agreed well with the simulation results. Dense 32-45-nm contact-hole (C/H)patterns were also successfully fabricated under annular illumination (σ=0.3/0.5). Due to astigmatic aberration, the C/Hpatterns were deformed at defocused positions, but they were almost circular at the best focus position. The flare of theprojection optics measured by the Kirk method was 11% over a flare range of 1-100 μm. The effects of the 11% flarewere evaluated using dark- and bright-field 32-nm L&S patterns. It was found that the top loss and line-width roughness(LWR) of the resist were larger for bright-field than for dark-field patterns. To reduce the impact of flare, we need EUVresists that are more robust with regard to flare. A comparison of the measured point spread function (PSF) of the flareand the calculated PSF revealed good agreement for long-range flare but some difference for short-range flare.