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24 March 2006 Optical measurements of critical dimensions at several stages of the mask fabrication process
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Critical dimension (CD) metrology is an essential part of the mask manufacturing process. We present a metrology solution based on broadband reflectometry, covering a wavelength range from 190 to 1000 nm, in one nanometer intervals. The analysis is performed using Forouhi-Bloomer dispersion equations, in conjunctions with Rigorous Coupled Wave Analysis (RCWA). The method provides accurate and repeatable results for critical dimensions, thickness, and optical properties (n and k spectra from 190 - 1000 nm) for all materials present in the structure. In terms of throughput (several seconds per point) and suitability for integration, the method has many advantages over conventional metrology techniques. Measurements were performed on two masks, at two different stages of the mask manufacturing process - After Etch Inspection (AEI) and After Strip Inspection (ASI). CD uniformity distribution maps at 121 points on the mask were obtained for 800 nm pitch grating arrays. The results were compared to conventional CD-SEM measurements collected at the same locations. A linearity study was conducted on 760 and 1120 nm pitch grating arrays with systematically increasing CD width. The results demonstrate excellent correlation with CD-SEM.
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John C. Lam and Alexander Gray "Optical measurements of critical dimensions at several stages of the mask fabrication process", Proc. SPIE 6152, Metrology, Inspection, and Process Control for Microlithography XX, 61523C (24 March 2006);


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