Simulation Study of Workfunction Variability in MOSFETs with Polycrystalline Metal Gates

The polycrystalline nature of the metal gate and the corresponding non-uniformity in the gate workfunction results in statistical variability in MOSFETs with high-!/metal gate stacks. Here the impact of the workfunction variation (WFV) associated with different gate grain orientations on the threshold voltage variation in a test bed 35 nm nMOSFETs is studied in details using full scale 3D numerical simulation. The workfunction-induced variability is compared with the variability introduced by other traditional sources of statistical variability including random discrete dopants (RDD) and line edge roughness (LER). Keywordsgranularity, metal gate, MOSFETs, variability, workfunction.

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