No abstract

Managing the total CD error in advanced mask manufacturing requires that error contributions from writing, process and metrology are minimized. This paper describes how both the writing and process contributions have been addressed in the Sigma7500 DUV laser pattern generator, which prints masks by imaging a programmable spatial light modulator (SLM). System enhancements have reduced the writing contribution to global CD uniformity to 5 nm (3s). Processrelated CD error sources, such as the signatures from mask developing and etching can be significant contributors to the total CD error in mask manufacturing. These errors are classified as being either pattern-independent or patterndependent, and the effects of both can be reduced using the ProcessEqualizer feature of the Sigma7500. This software tool performs CD sizing during writing based on pattern density maps derived during mask data preparation, along with tunable parameters that are determined experimentally. The CD sizing function has no effect on system throughput and does not require flattening and re-fracturing of the pattern data.

No abstract

No abstract

Optical proximity correction (OPC) is widely used in wafer lithography to produce a printed image that best matches the design intent while optimizing CD control. OPC software applies corrections to the mask pattern data, but in general it does not compensate for the mask writer and mask process characteristics. The Sigma7500-II deep-UV laser mask writer projects the image of a programmable spatial light modulator (SLM) using partially coherent optics similar to wafer steppers, and the optical proximity effects of the mask writer are in principle correctable with established OPC methods.To enhance mask patterning, an embedded OPC function, LinearityEqualizer™, has been developed for the Sigma7500-II that is transparent to the user and which does not degrade mask throughput. It employs a Calibre™ rule-based OPC engine from Mentor Graphics, selected for the computational speed necessary for mask run-time execution. A multinode cluster computer applies optimized table-based CD corrections to polygonized pattern data that is then fractured into an internal writer format for subsequent data processing. This embedded proximity correction flattens the linearity behavior for all linewidths and pitches, which targets to improve the CD uniformity on production photomasks.Printing results show that the CD linearity is reduced to below 5 nm for linewidths down to 200 nm, both for clear and dark and for isolated and dense features, and that sub-resolution assist features (SRAF) are reliably printed down to 120 nm. This reduction of proximity effects for main mask features and the extension of the practical resolution for SRAFs expands the application space of DUV laser mask writing.