Diffusion of oxygen in aluminum nitride

In this study, we investigate the thermal diffusion behavior of oxygen in bulk aluminum nitride (AlN) using an aluminum oxide (Al2O3) coating layer as an oxygen source. We used dynamic secondary ion mass spectrometry (D-SIMS) and time-of-flight SIMS (ToF-SIMS) for accurate profiling of the oxygen concentration across the Al2O3/AlN interface of as-grown and annealed samples. Initial tailing and limited dynamic range of ToF-SIMS measurements due to oxygen redeposition was addressed by employing an optimized dual-beam sputtering strategy with staged crater resizing. This eliminates all adverse effects and allows achieving detection sensitivity and depth resolution comparable to D-SIMS. Additional artifacts in the chemical profiling arise from surface roughening and localized phase transitions from amorphous Al2O3 to partially crystalline AlxOy induced by the high-temperature annealing, which are supported by correlative AFM (atomic force microscopy) and TEM (transmission electron microscopy) analyses. Eliminating all these factors reveals that, upon high-temperature annealing, a limited thermal diffusion of oxygen into AlN occurs after 12 h at 1600°C, or after 4 and 1 h at 1700°C, respectively, indicating an oxygen diffusion coefficient below 1.8×10−16cm2s−1 under these conditions.