Existing photomask metrology is struggling to keep pace with the rapid reduction ofudIC dimensions as traditional measurement techniques are being stretched to theirudlimits. This thesis examines the use of on-mask probable electrical test structuresudand measurement techniques to meet this challenge and to accurately characteriseudthe imaging capabilities of advanced binary and phase-shifting chrome-on-quartzudphotomasks. On-mask, electrical and optical linewidth measurement techniques haveudhighlighted that the use of more than one measurement method, complementing eachudother, can prove valuable when characterising an advanced photomask process.udIndustry standard optical metrology test patterns have been adapted for the directudelectrical equivalent measurement and the structures used to characterise differentudfeature arrangements fabricated on standard and advanced photomasks with proximityudcorrection techniques. The electrical measurements were compared to measurementsudfrom an optical mask metrology and verification tool and a state-of-the-art CD-AFMudsystem and the results have demonstrated the capability and strengths of the on-maskudelectrical measurement. For example, electrical and AFM measurements on submicronudfeatures agreed within 10nm of each other while optical measurements were offset byudup to 90nm. Hence, electrical techniques can prove valuable in providing feedback toudthe large number of metrology tools already supporting photomask manufacture, whichudin turn will help to develop CD standards for maskmaking.udElectrical test structures have also been designed to enable the characterisation ofudoptical proximity correction to characterise right angled corners in conducting tracksudusing a prototype design for both on-mask and wafer characterisation. Measurementudresults from the on-mask structures have shown that the electrical technique is sensitiveudenough to detect the effect of OPC on inner corners and to identify any defects in theudfabricated features. For example less than 10ud (5%) change in the expected resistanceuddata trends indicated a deformed OPC feature. Results from on-wafer structures haveudshown that the correction technique has an impact on the final printed features andudthe measured resistance can be used to characterise the effects of different levels ofudcorrection. Overall the structures have shown their capability to characterise this typeudof optical proximity correction on both mask and wafer level.udTest structures have also been designed for the characterisation of the dimensionaludmismatch between closely spaced photomask features. A number of photomasksudwere fabricated with these structures and the results from electrical measurementsudhave been analysed to obtain information about the capability of the mask makingudprocess. The electrical test structures have demonstrated the capability of measuringudtool and process induced dimensional mismatches in the nanometer range on masksudwhich would otherwise prove difficult with standard optical metrology techniques. Forudexample, electrical measurements detected mismatches of less than 15nm on 500nmudwide features.
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