Characterization of nitrided silicon-silicon dioxide interfaces
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INTRODUCTION Measurements of minority carrier recombination lifetime are sensitive to both bulk and surface recombination, so in principle these techniques can be used for the simultaneous characterization of bulk and surface properties, provided bulk and surface contributions are accurately separated. For what concerns bulk properties, photocurrent measurements have been commonly used for a few years in the Elymat technique (Electrolytic Metal Tracer) [1]. Recently, it was shown that this technique can be extended to the evaluation of surface recombination velocity, in addition to bulk recombination lifetime. A new, nondestructive method for evaluating both surface recombination velocity and bulk minority carrier lifetime by photocurrent measurements was proposed and validated by comparison with capacitance-voltage measurements of interface state density [2]. This method consists of measurements of surface recombination velocity under an applied surface bias. The application of a surface bias allows the control of the interface potential and the identification of the suitable interface condition such that the surface recombination velocity can be considered as a measurement of interface state density. This method allows the characterization
207 Mat. Res. Soc. Symp. Proc. Vol. 591 02000 Materials Research Society
of the oxide-silicon interface to be obtained without the formation of a capacitor structure. It is known [3] that the capacitor process can alter interface properties, so a method that does not require further processing after the dielectric growth is very suitable for the study of as-grown interfaces. For this reason in this work we use the photocurrent-based measurement of surface recombination velocity in the characterization of a new technology for dielectric growth, i.e. the Rapid Thermal Oxidation (RTO) and Nitridation (RTN) of the silicon surface. A previous work concerning furnace nitridation of oxide-silicon interfaces showed that [4] surface recombination velocity (hence surface state density) is reduced as nitridation proceeds, so surface recombination velocity data give information about interface nitridation. However this information is indirect, and for this reason we compare surface recombination velocity data with nitrogen concentration at the oxide-silicon ifiterface obtained by Secondary Ion Mass Spectroscopy (SIMS) measurements. Surface recombination velocity data are a measure of interface state density at the as-grown interface, and it is to be expected that interface state density will evolve during device processing. As the electrical performances of devices are strongly affected by the presence of Si-Si0 2 interface states, the link between results concerning the as-grown interface and electrical data on fully processed wafer (in terms of both device characterization and reliability) needs to be clarified. As expected after a complete device process surface states are suppressed by hydrogen passivation obtained by a forming gas annealing, however it will be shown that they are r
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