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20 October 2006 Contact hole CD and profile metrology of binary and phase shift masks: effect of modeling strategies in application of scatterometery
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Scatterometers are widely used for line/space or 2D structure measurements in both wafer and mask industries. This technology is now gaining more acceptance and is being applied 3D structures such as contacts and pads. Contact CDs and trench depth in photomasks are critical monitoring parameters in mask industry and are discussed here. We are reporting contact CDs and profile results measured from targets from Binary, PSM, and Crless plates. The strategies of model creation such as using simple trapezoid versus more advanced shapes affect how well SWA and footings can be measured and reported from these structures. We are reporting CD and profile information obtained with Scatterometer, and then comparing CD SEM, AFM, and cross section SEM. Multiple different modeling configurations were used with different levels of complexity, and we report on optimum modeling strategy to obtain profile information from 3D structures. The relationship between the modeling strategy versus cross correlation between different parameters is discussed. CD linearity, uniformity, and other correlation parameters to the reference CD SEM tool are reported. Target CDs ranged from 60nm up to 600nm. CD uniformity reported from Scatterometry is 20~30% less than that from CD SEMs. This CD uniformity improvement is due to the fact that scatterometer beam samples dozens to hundreds of samples and 'averages' profile parameters, thus eliminating local effect such as line edge roughness. Contact depth are also measured and compared to AFM, in which the bias between the two tools are usually around 3nm or less. In terms of smallest target CD measurable, in this paper we report routine measurement of small contacts with middle CD down to 65nm (bottom CD close to 50nm) with both RP and SE mode. Application of scatterometry method to mask contacts and pads leads to accurate and fast measurement of 3D profiles, and opens up possibility of in-line monitoring of profile information due to the higher runrate compared to traditional metrology tools.
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Kyung-man Lee, Sanjay Yedur, Malahat Tavassoli, Kiho Baik, and Milad Tabet "Contact hole CD and profile metrology of binary and phase shift masks: effect of modeling strategies in application of scatterometery", Proc. SPIE 6349, Photomask Technology 2006, 63490M (20 October 2006);

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