Pellicle contribution to optical proximity and critical dimension uniformity for 1.35 numerical aperture immersion ArF lithography

摘要

Pellicles are mounted on the masks used in ArF lithographynfor integrated circuit manufacturing to ensure defect-free printing. Thenpellicle, a thin transparent polymer film, protects the reticle from dust.nBut, as the light transmittance through the pellicle has an angular depen-ndency, the pellicle also acts as an apodization filter. In the current work,nwe present both experimental and simulation results at 1.35 numericalnaperture immersion ArF lithography showing the influence of two typesnof pellicles on proximity and intra-die critical dimension uniformity (CDU).nTo do so, we mounted and dismounted the different pellicle types on onenand the same mask. The considered structures on wafer are compatiblenwith the 32-nm logic node for poly and metal. For the standard ArF pelliclen(thickness 830 nm), we experimentally observe a distinct effect of severalnnm due to the pellicle presence on both the proximity and the intra-dienCDU. For the more advanced pellicle (thickness 280 nm), no signature ofnthe pellicle on proximity or CDU could be found. By modeling the pellicle’snoptical properties as a Jones Pupil, we are able to simulate the pellicle ef-nfects with good accuracy. These results indicate that for the 32-nm node,nit is recommended to take the pellicle properties into account in the opticalnproximity correction calculation when using a standard pellicle. In addition,nsimulations also indicate that a local dose correction can compensate tona large extent for the intra-die pellicle effect. When using the more ad-nvanced thin pellicle (280 nm), no such corrections are needed