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30 October 2007 Calibration of contact areas: the influence of corner rounding
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The precise reporting of critical dimension (CD) features on photolithographic masks is an essential part of the mask production process. A wide range of external (standardization by national institutes) and internal (standardization within mask houses to match different tools) methods has been set up to ensure calibration consistency for the simple one dimensional case. One of the current developments is to expand these concepts to area measurements. This is to achieve better reproducibility of CD tools and to achieve a better characterization of contacts with respect to their imaging behaviour in wafer scanners. Here, we report some very fundamental constrains of this approach that have to be taken into account regardless of the actual measurement strategy. The major result is that for two dimensional contacts the shape has to be considered. This is due to the fact that the usually constant offset for calibration of critical dimensions in one dimension is no longer a constant but depends on the absolute size of the contact and the value of the corner rounding. For standard values of 200 nm contacts with corner rounding of 75 nm and calibration offsets around 20 nm maximum systematic differences of about 2nm will be obtained. Given the fact that even 40 nm calibration differences for photomask standards can be observed even for national institutes, these systematic errors can be easily as large as 6 nm for 200 nm structures. This systematic error clearly exceeds the road map targets for critical dimension off-target specifications for the coming technology node. This statement is even emphasized by the fact that in future contact layer specifications will be smaller than for lines/space layers. Once tool independent characterization of contact areas has to be achieved, area measurement in each mask house needs a second thought to implement these systematic constrains. Here, we show that the additional measurement of the corner rounding ís a relatively easy method to accomplish this.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jan Richter, Eva-Maria Zerbe, and Thomas Marschner "Calibration of contact areas: the influence of corner rounding", Proc. SPIE 6730, Photomask Technology 2007, 67303B (30 October 2007);

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