Dependence of the hardness of AlxGa1−xAs on composition and effect of oxidation

The mechanical properties of semiconductor materials determine the reliability of microelectronics. The hardness of Al1−xGaxAs is investigated together with oxidation and its effect on this parameter. A structure consisting of three AlxGa1−xAs layers of different composition separated by In0.01Ga0.99As etch stops was deposited via metal-organic vapor phase epitaxy. High resolution x-ray diffraction determined the composition of the baseline layers to be Al0.9Ga0.1As, Al0.8Ga0.2As and Al0.7Ga0.3As. Nanoindentation measurements demonstrated that hardness decreases with aluminum content following a linear correlation. To study the effect of oxidation on hardness, two samples of Al0.8Ga0.2As were oxidized in air at 475 °C for 2 and 4 h. The surface morphology of the oxide imaged using atomic force microscopy was granular. X-ray diffraction simulated curves estimated the Al0.8Ga0.2As thickness decrease due to oxidation. The growth of the oxide layer was linear with time indicating that the process is reaction-rate limited and the layer is porous. The hardness of the (Al0.8Ga0.2)2O3 oxide was extrapolated to be more than twice the value of the baseline sample.