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Abstract-We present an efficient and accurate method to characterize the physical thickness of ultrathin gate oxides (down to 25Å) and the effective polysilicon doping of advanced CMOS devices. The method is based on the model for Fowler-Nordheim (F-N) tunneling current across the gate oxide with correction in gate voltage to account for the polysilicon-gate depletion. By fitting the model to measured data, both the gate oxide thickness and the effective poly doping are unambiguously determined. Unlike the traditional capacitance-voltage (C0V ) technique that overestimates thin-oxide thickness and requires large area capacitor, this approach results in true physical thickness and the measurement can be performed on a standard sub-half micron transistor. The method is suitable for oxide thickness monitoring in manufacturing environments.

This work shows that the worst-case gate voltage stress condition for LDD nMOSFETs is a strong function of the channel length, drain voltage, and operating temperature. A new cross-over behavior of the worst-case gate voltage condition is reported at low temperatures. New understanding of the hot-carrier mechanisms at low temperatures is also discussed. Low temperature effects such as freeze-out are shown to have important contributions to the hot-carrier behavior at low temperatures. A trend is identified for the first time which suggests important consequences for the hot-carrier reliability of deep sub-micron channel length MOSFETs under normal operating temperatures.

In this paper, we report performance and reliability of sub-lOOnm MOSFETs with ultra thin direct tunneling (DT) gate oxides. Both pure oxides and nitrided oxides down to 17A were investigated. For a L, of about 90nm (Leff of about 50nm), a drive current of larger than 1.OmAIpm and a transconductance of higher than 800mSImm were obtained at room temperature. Channel electron transport properties were investigated. High field mobility degradation with decrease of oxide thickness and subsequent improvement with use of nitrided oxides were observed. Reliability characteristics such as gate leakage, stress-induced-leakage, and hot-carrier degradation are described. A new mechanical stress induced leakage phenomenon for ultra thin DT oxides was revealed.