Thin (2–10 nm) silicon nitride films have been grown by repetitive plasma nitridation of Si using a NH3 remote plasma and deposition of Si by a SiH2Cl2 thermal reaction. The deposition rate is self-limited at nearly half-molecular layer (ML) per one deposition cycle. The process window for the half-ML/cycle of growth has been investigated with respect to the NH3 plasma power, SiH2Cl2 exposure time, and substrate temperature. The thickness fluctuation of the film over a 2 in. wafer is within measurement accuracy of the ellipsometer (± 1.9%) for the atomic layer controlled film while it is ± 8.5% for all the remote-plasma chemical vapor deposition film.

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We report on a new roadblock which will limit the gate oxide thickness scaling of MOSFETs. It is found that statistical distribution of direct tunnel leakage current through 1.2 to 2.8 nm thick gate oxides induces significant fluctuations in the threshold voltage and transconductance when the gate oxide tunnel resistance becomes comparable to gate poly-Si resistance. By calculating the measured tunnel current based on multiple scattering theory, it is shown that the device characteristics fluctuations will be problematic when the gate oxide thickness is scaled down to less than 1 nm.