Thermal oxidation of polycrystalline and single crystalline aluminum nitride wafers

Abstract

Two types of aluminum nitride (AlN) samples were oxidized in flowing oxygen between 900°C and 1150°C for up to 6 h-highly (0001) textured polycrystalline AlN wafers and low defect density AlN 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 AlN. At 1100°C and 1150°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 AlN single crystals resulted in a more uniform colored oxide layer compared to polycrystalline AlN. The aluminum oxide layer was crystalline with a rough AlN/oxide interface. The orientation relationship between AlN and Al 2 O 3 was (0001) AlN//(101 -0) Al 2 O 3 and (11 -00) AlN//(011 -2) Al 2 O 3 .

Oxidation kinetics of aluminum nitride at different oxidizing atmosphere

“…Therefore, the study of AlN oxidation is of great interest for both fundamental science and practical applications. Several articles have reported the oxidation behavior of AlN, both in powder form and as bulk ceramic [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Among these studies, many techniques including X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been employed to study the oxidation phenomenon.…”

“…These studies have determined the crystalline state of the oxide, the composition and chemical bonding states of Al, N, and O atoms, and have developed simple oxidation kinetics rate models. Because the oxidation process is affected by parameters such as: particle size, temperature, the humidity of environment, and characteristics of the sample [5][6][7][8][9][10][11][12][13][14][15][16][17], various kinetics models (linear or parabolic) have been proposed. Kim and Moorhead [12] reported that the oxidation kinetics of sintered aluminum nitride followed linear rate law while at higher temperature became parabolic.…”

X-Ray Photoelectron Spectroscopy Characterization of Aluminum Nitride Surface Oxides: Thermal and Hydrothermal Evolution

“…A transition temperature of 65°C for conversion of Al(OH) 3 to AlOOH was calculated by Fukumoto et al 6 Slack and McNelly 2 reported that AlN single crystals formed a 50-100 Å thick protective layer of Al 2 O 3 upon room temperature exposure to air, based on optical ellipsometry measurements. The hightemperature oxidation of polycrystalline and singlecrystal AlN wafers was studied by Gu et al, 7 who reported that a layer of Al 2 O 3 formed on the surface after oxidation in flowing oxygen at temperatures above 900°C. In an x-ray photoelectron spectroscopy (XPS) study of AlN thin films grown on SiC, King et al 8 presented data showing that surface oxygen was bonded to Al in both O 2-and OH -chemical states, which indicated the presence of a hydrated oxide, i.e., a hydroxide.…”

Growth of bulk AlN single crystals with low oxygen content taking into account thermal and kinetic effects of oxygen-related gaseous species

“…In particular, a more intensive yellowish coloration was found in volume parts that were grown on crystal faces exhibiting lower growth rates. Furthermore, Gu et al [18] studied the oxidation kinetics of AlN single crystals between 900 and 1150 1C and observed faster oxidation rates at N-faces compared to Al-faces. As a consequence, the influence of oxygen-related species is also different when comparing growth of single crystal parts grown on different facets.…”