MPPC technique for gate etch process monitoring using CD-SEM images and its validity verification

The effectiveness of multiple parameter profile characterization (MPPC) as a three-dimensional measurement technique for etched gates is examined by comparison of shape indices with device performance. The MPPC method derives shape indices from top-down, critical-dimension scanning electron microscopy (CD-SEM) images to characterize the sidewall angle and footing roundness of the gate, which are considered to be the structural features that have a great effect on device performance. The capabilities of the proposed method are evaluated through experiments using processed gate wafers etched under different conditions, comparing the shape indices with the cross-sectional profiles obtained by atomic force microscopy. The relationship between the MPPC indices and threshold voltage is also investigated, confirming that variations in sidewall angle and footing roundness have several times the impact on threshold voltage as line width variation. This study confirms the importance of three-dimensional measurement of gate profiles for process monitoring through the use of a method such as MPPC.