X-RAY-LITHOGRAPHY MASK METROLOGY - USE OF TRANSMITTED ELECTRONS IN ANSEM FOR LINEWIDTH MEASUREMENT

X-ray masks present a measurement object that is different from most o ther objects used in semiconductor processing because the support memb rane is, by design, x-ray transparent. This characteristic can be used as an advantage in electron beam-based x-ray mask metrology since, de pending upon the incident electron beam energies, substrate compositio n and substrate thickness, the membrane can also be essentially electr on transparent. The areas of the mask where the absorber structures ar e located are essentially x-ray opaque, as well as electron opaque. Th is paper shows that excellent contrast and signal-to-noise levels can be obtained using the transmitted-electron signal for mask metrology r ather than the more commonly collected secondary electron signal. Mont e Carlo modeling of the transmitted electron signal was used to suppor t this work in order to determine the optimum detector position and ch aracteristics, as well as in determining the location of the edge in t he image profile. The comparison between the data from the theoretical ly-modeled electron beam interaction and actual experimental data were shown to agree extremely well, particularly with regard to the wall s lope characteristics of the structure. Therefore, the theory can be us ed to identify the location of the edge of the absorber line for linew idth measurement. This work provides one approach to improved x-ray ma sk linewidth metrology and a more precise edge location algorithm for measurement of feature sizes on x-ray masks in commercial instrumentat ion. This work also represents an initial step toward the first SEM-ba sed accurate linewidth measurement standard from NIST, as well as prov iding a viable metrology for linewidth measurement instruments of x-ra y masks for the lithography community.