Impact of EUV light scatter on CD control as a result of mask density changes

Abstract

The Power Spectral Density (PSD) function for a large-field EUV exposure system is used to compute the impact of flare on critical dimension (CD) control for masks exhibiting Cr density changes that result in cross-field flare variation. It is shown that open field flare must be controlled to 11 percent for 30 nm isolated features and 6 percent for 20 nm isolated features for an NA equals 0.25 system assuming a +/- 3 percent CD control budget allocated to flare. Based on these results individual mirror surface roughness specifications for the mid-spatial frequencies of about 0.14 and 0.11 nm RMS, respectively, are needed for future chip production. This paper also discusses that either mask 'dummification' or CD resizing can be applied to minimize the effects of flare on CD control in case mirror fabrication targets may be difficult to achieve.