22 March 2008 Characterization of 32nm node BEOL grating structures using scatterometry
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Implementations of scatterometry in the back end of the line (BEOL) of the devices requires design of advanced measurement targets with attention to CMP ground rule constraints as well as model simplicity details. In this paper we outline basic design rules for scatterometry back end targets by stacking and staggering measurement pads to reduce metal pattern density in the horizontal plane of the device and to avoid progressive dishing problems along the vertical direction. Furthermore, important characteristics of the copper shapes in terms of their opaqueness and uniformity are discussed. It is shown that the M1 copper thicknesses larger than 100 nm are more than sufficient for accurate back end scatterometry implementations eliminating the need for modeling of contributions from the buried layers. AFM and ellipsometry line scans also show that the copper pads are sufficiently uniform with a sweet spot area of around 20 μm. Hence, accurate scatterometry can be done with negligible edge and/or dishing contributions if the measurement spot is placed any where within the sweet spot area. Reference metrology utilizing CD-SEM and CD-AFM techniques prove accuracy of the optical solutions for the develop inspect and final inspect grating structures. The total measurement uncertainty (TMU) values for the process of record line width are of the order of 0.77 nm and 0.35 nm at the develop inspect and final inspect levels, respectively.
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Shahin Zangooie, Shahin Zangooie, Matthew Sendelbach, Matthew Sendelbach, Matthew Angyal, Matthew Angyal, Charles Archie, Charles Archie, Alok Vaid, Alok Vaid, Itty Matthew, Itty Matthew, Pedro Herrera, Pedro Herrera, } "Characterization of 32nm node BEOL grating structures using scatterometry", Proc. SPIE 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 69220S (22 March 2008); doi: 10.1117/12.773088; https://doi.org/10.1117/12.773088

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