Effect of post-oxidation annealing of the oxynitride onthe C-V and G-V characteristicsof Al/thin oxynitride/n-Si tunnel diodes

Abstract

Ultrathin oxynitrides have several advantages over conventionaloxides of silicon. In this paper we report the resultsof ultrathin (2.7 nm) oxynitride films grown on n-Si by N2Oplasma-assisted oxidation at 200 °C. Theoxynitride is characterized by fabricating Al/thin oxynitride/n-Si tunnel diodes and measuring thecapacitance-voltage (C-V) and conductance-voltage (G-V)characteristics in the frequency range 10 kHz to 1 MHz. Thesetunnel diodes with `as-grown' oxide have shown a frequencydependence in C-V characteristics, indicating a high({>}1012 cm-2 eV-1) interface state density (Dit). The effect of series resistance on the accumulation capacitance of the tunnel diodes is also studied. The density ofinterface states ({D}it) is estimated from the G-V characteristics at 10 kHz. Annealing of these oxynitrides (calledpost-oxidation annealing (POA)) is found to have a profoundeffect on the interface state density (Dit) and fixedoxide charge density (Qf). The POA is carried out in thetemperature range 300-650 °C in ambient nitrogen for 20 min. The tunnel diodes with POA oxide showed littlefrequency dependence in the C-V characteristics; thisobservation is attributed to the reduction in the interfacestate density (~5×1011 cm-2 eV-1) dueto POA. The fixed oxide charge (Qf) has been evaluatedfrom the C-V characteristics. It is observed that Qfhas a minimum value (~2.2×1012 cm-2) when theoxynitride is annealed at 350 °C.