Optical EngineeringConcept of two-dimensional swing curves for critical dimension prediction and optimization of resist/antireflective coating bilayers in topographic situations
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In microlithography, the necessity of using bottom antireflective coatings (BARCs) to reduce linewidth variations resulting from reflective notching and thin film interference effects has been largely demonstrated. We report a new methodology, based on a 2-D swing curve concept, to predict the lithographic performance of resist/BARC bilayers in a topographic situation to optimize the critical dimension (CD) range. Due to inherent planarization effects when coating on topography, both the resist and organic BARC thicknesses vary, as do the final reflectivity and CDs. As a consequence, it is not easy to determine the optimal BARC thicknesses and to predict the lithographic performance, taking into account topography effects over the whole chip. Usually, lithographic performance (CD swing curves) is measured or calculated using modeling over plane wafers. Over the topography of a real chip, however, the resist thickness can cover up to four periods of the swing curve, which means that lithographic performance over a real chip cannot be predicted using swing curves calculated or measured on plane wafers. We therefore propose a new method of representing the reflectivity and CD swing curves in two dimensions to evaluate the lithographic performance of the BARC/resist bilayer. A simulation algorithm is performed that enables the determination of both the optimal BARC thicknesses and the lithographic performance window over the whole chip. Practical examples are given demonstrating the role of such a simulation.