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

摘要

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 N_2O plasma-assisted oxidation at 200℃. The oxynitride is characterized by fabricating Al/thin oxynitride-Si tunnel diodes and measuring the capacitance--voltage (C--V) and conductance--voltage (G--V) characteristics in the frequency range l0 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℃ 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 (～5 × 10~11 cm~-2 eV~-1 ) due to POA. The fixed oxide charge (Q_f) has been evaluated from tlie C--V characteristics. It is observed that Q_f has a minimum value (～2.2 × 10~12 cm~-2) when the oxynitride is annealed at 350℃.