The impact of sub monolayers of HfO/sub 2/ on the device performance of high-k based transistors [MOSFETs]

Thin layers of ALCVD/spl trade/ HfO/sub 2/ were deposited on top of 1.5 nm SiON. At 5 growth cycles - resulting in less than 1 monolayer of HfO/sub 2/ - the mobility is as low as 70% of the SiON control. Simulation results show that a fixed charge density of 3/spl times/10/sup 13/ cm/sup -2/ at the poly-Si/HfO/sub 2/ interface can explain this behavior. Two different kinds of poly-Si - in situ doped and implanted - result in different inversion capacitance. Both poly-Si varieties show similar VT shifts and mobility reduction. However, for in situ doped poly-Si, no poly depletion is observed whereas for implanted poly-Si it is.

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