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

Ultrathin oxynitrides have several advantages over conventional oxides of silicon. In this paper we report the results of ultrathin (2.7 nm) oxynitride films grown on n-Si by N2O plasma-assisted oxidation at 200 °C. The oxynitride is characterized by fabricating Al/thin oxynitride/n-Si tunnel diodes and measuring the capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics in the frequency range 10 kHz to 1 MHz. These tunnel diodes with `as-grown' oxide have shown a frequency dependence 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 of interface states (Dit) is estimated from the G-V characteristics at 10 kHz. Annealing of these oxynitrides (called post-oxidation annealing (POA)) is found to have a profound effect on the interface state density (Dit) and fixed oxide charge density (Qf). The POA is carried out in the temperature range 300-650 °C in ambient nitrogen for 20 min. The tunnel diodes with POA oxide showed little frequency dependence in the C-V characteristics; this observation is attributed to the reduction in the interface state density (approximately 5×1011 cm-2 eV-1) due to POA. The fixed oxide charge (Qf) has been evaluated from the C-V characteristics. It is observed that Qf has a minimum value (approximately 2.2×1012 cm-2) when the oxynitride is annealed at 350 °C.