Tunnel Oxide Growth on Silicon With “Wet Nitrous Oxide” Process for Improved Performance Characteristics

Abstract

In this letter, the authors present the process, growth kinetics, and electrical characteristics of tunnel oxides grown by furnace oxidation of silicon at 800 • C in an ambient of nitrous oxide (N 2 O) and water vapor. Tunnel oxides of thickness 82-92 Å are grown by this "wet N 2 O oxidation" process, and the electrical characteristics such as the capacitance-voltage, current-voltage, voltage ramp, time-dependent dielectric breakdown, and charge to breakdown are evaluated using MOS capacitor as the diagnostic device. The results obtained clearly demonstrate superior performance characteristics of this oxide for Flash memory applications, with excellent charge to breakdown and minimum change in the gate voltage during constant current stressing.Index Terms-Dielectric breakdown, leakage currents, timedependent dielectric breakdown (TDDB), tunnel oxide nitridation, wet thermal oxidation.

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“…The survey also showed that it involved rather high temperature processes. In this paper we first give a brief account of a low temperature nitridation technology recently developed in our laboratory [19]. This process enables the growth of reliable tunnel oxides of thickness in the range 6 In this 'wet N 2 O' oxidation process, (100) p-type silicon is oxidized in a furnace at 800°C , in a gas mixture of N 2 O and water vapor by passing into the furnace 20 liters of N 2 O and 20 liters of N 2 bubbled thorough deionized (D.I.)…”

“…The presence of N 2 O enables incorporation of controlled quantities of nitrogen into the oxide during the wet oxidation process which can be carried out at temperatures in the range 750 to 800°C to achieve oxide thickness control. Based on detailed experimental studies with this process it has been established [19] that oxide thickness ranging from 2 nm to 9.5 nm can be achieved with very good uniformity on silicon cut pieces of 2 cm 2cm × size. The role played by N 2 O on the oxidation process is indeed ascertained by an increase in the oxidation rate observed [20] as shown in Fig.1 when the N 2 O gas flow rate is increased from 0 to 20 liters per hour while the flow rate of N 2 bubbled through de-ionized (D.I.)…”