7 July 1997 CMP overlay metrology: robust performance through signal and noise improvements
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Historically, effective overlay registration measurement of chemical mechanical polish (CMP) processes has posed a challenge to optical based metrology systems. This is primarily due to the extreme planarization process of CMP which produces very small transition step heights between adjacent features resulting in a very low signal differential. The repeatability and accuracy of overlay measurements is intimately relate to the signal to noise ratio and the signal to interference ration of the acquired data. Measurement performance of CMP overlay targets was improved through enhancement of the optical signal and electronic noise reduction. Hewlett Packard provided a series of wafers having a range of tungsten deposition thickness and CMP processing. These were measured on the IVS-120 fully automated optical metrology system to quantify the effects of the improvements. The result was overlay registration measurement repeatability which was typically better than 3 nanometers 3-(sigma) and tool induced shift of less than 1 nanometer.
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John C. Podlesny, John C. Podlesny, Francis Cusack, Francis Cusack, Susan Redmond, Susan Redmond, } "CMP overlay metrology: robust performance through signal and noise improvements", Proc. SPIE 3050, Metrology, Inspection, and Process Control for Microlithography XI, (7 July 1997); doi: 10.1117/12.275947; https://doi.org/10.1117/12.275947

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