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5 November 2005 Image imbalance compensation in alternating phase-shift masks towards the 45nm node through-pitch imaging
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The use of an Alternating Phase-Shift Mask (AltPSM) is a strong resolution enhancement technique combining high contrast and a low Mask Error Enhancement Factor with a large focus depth. However, image (or intensity) imbalance, which is intrinsically related to AltPSM imaging, is known to produce focus-dependent feature shifts. The evolution towards hyper NA immersion lithography systems and the associated shrinkage of feature sizes and pitches also puts stronger demands on the placement of the printed features, in order to meet the overlay requirements. Therefore, a good image imbalance reduction strategy is important for a successful implementation of AltPSM in manufacturing. A first step towards this implementation is to find a through-pitch imaging solution guaranteeing both the line width and line position to be within CD and overlay specifications in a sufficiently large dose-focus window. In this paper, we present a strategy to evaluate AltPSM imaging results by monitoring the edge displacement of the printed feature caused by image imbalance. The proposed method insures correct line printing within the calculated process window, taking image imbalance into account. We experimentally assess the imaging performance of a current state-of-the-art dry etched AltPSM with a nominal trench bias on a 0.85 NA immersion scanner. The results demonstrate that a through-pitch solution for printing 65 nm lines on wafer from P140 nm to isolated lines exists that meets both the CD and overlay requirements. Moreover, we have developed a methodology that effectively solves the image imbalance using a pitch-dependent trench bias in combination with an optimized etch depth, which should be chosen in accordance with the dose used for printing the 65 nm line.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Lieve Van Look, Bryan Kasprowicz, Axel Zibold, Wolfgang Degel, and Geert Vandenberghe "Image imbalance compensation in alternating phase-shift masks towards the 45nm node through-pitch imaging", Proc. SPIE 5992, 25th Annual BACUS Symposium on Photomask Technology, 59921S (5 November 2005);

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