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 degrees 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 (>10(12) cm(-2) eV(-1)) interface state density (D-it). The effect of series resistance on the accumulation capacitance of the tunnel diodes is also studied. The density of interface states (D-it) 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 (D-it) and fixed oxide charge density (Q(f)). The POA is carried out in the temperature range 300-650 degrees 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 (similar to 5 x 10(11) cm(-2) eV(-1)) due to POA. The fixed oxide charge (Q(f)) has been evaluated from the C-V characteristics. It is observed that Q(f) has a minimum value (similar to 2.2 x 10(12) cm(-2)) when the oxynitride is annealed at 350 degrees C.