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28 March 2017 SAQP pitch walk metrology using single target metrology
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Self-aligned quadruple patterning (SAQP) processes have found widespread acceptance in advanced technology nodes to drive device scaling beyond the resolution limitations of immersion scanners. Of the four spaces generated in this process from one lithography pattern two tend to be equivalent as they are derived from the first spacer deposition. The three independent spaces are commonly labelled as α, β and γ. α, β and γ are controlled by multiple process steps including the initial lithographic patterning process, the two mandrel and spacer etches as well as the two spacer depositions. Scatterometry has been the preferred metrology approach, however is restricted to repetitive arrays. In these arrays independent measurements, in particular of alpha and gamma, are not possible due to degeneracy of the standard array targets. . In this work we present a single target approach which lifts the degeneracies commonly encountered while using product relevant layout geometries. We will first describe the metrology approach which includes the previously described SRM (signal response metrology) combined with reference data derived from CD SEM data. The performance of the methodology is shown in figures 1-3. In these figures the optically determined values for alpha, beta and gamma are compared to the CD SEM reference data. The variations are achieved using controlled process experiments varying Mandrel CD and Spacer deposition thicknesses.
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Fang Fang, Pedro Herrera, Taher Kagalwala, Janay Camp, Alok Vaid, Stilian Pandev, and Franz Zach "SAQP pitch walk metrology using single target metrology", Proc. SPIE 10145, Metrology, Inspection, and Process Control for Microlithography XXXI, 101452R (28 March 2017);

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