Thermal oxidation of polycrystalline and single crystalline aluminum nitride wafers

Two types of aluminum nitride (AlN) samples were oxidized in flowing oxygen between 900 degrees C and 1150 degrees C for up to 6 h-highly (0001) textured polycrystalline AIN wafers and low defect density AIN single crystals. The N-face consistently oxidized at a faster rate than the Al-face. At 900 C and 1000 C after 6 h, the oxide was 15% thicker on the N-face than on the Al-face of polycrystalline AIN. At 1100 degrees C and 1150 degrees C, the oxide was only 5% thicker on the N-face, as the rate-limiting step changed from kinetically-controlled to diffusion-controlled with the oxide thickness. A linear parabolic model was established for the thermal oxidation of polycrystalline AlN on both the Al- and N-face. Transmission electron microscopy (TEM) confirmed the formation of a thicker crystalline oxide film on the N-face than on the Al-face, and established the crystallographic relationship between the oxide film and substrate. The oxidation of high-quality AIN single crystals resulted in a more uniform colored oxide layer compared to polycrystalline AlN. The aluminum oxide layer was crystalline with a rough AIN/oxide interface. The orientation relationship between AlN and Al2O3 was (0001) AlN//$(1010) over bar $ Al2O3 and $(1100) over bar $ AlN//$(0112) over bar $ Al2O3.