Infrared studies of laser induced oxide on (1 0 0) Si and SiGe layers

Oxide layers have been grown on single crystal (1 0 0) Si and SiGe surfaces with exposure to a pulsed UV laser at 266 nm under various controlled environments. During the growth, sample surfaces were first melted by the laser power. Oxygen related species then diffused into the melt. Oxide was formed after the samples re-solidified. Besides the strong stretching mode absorption at 1080 cm−1 (T2 mode), there was an intense shoulder around 1200 cm−1 (the A1 mode) in the Fourier transform infrared spectrum, compared to thermal oxide. The relative intensity of the shoulder decreased with ambient water vapor concentration. The porosity of this oxide leads to the intense shoulder and more water vapor incorporation can decrease the porosity. The porous oxide could be annealed to some extent with a high-temperature thermal process. Because the adsorption and diffusion of water molecules to and in melted silicon are easier than oxygen molecules, ambient water vapor can fill the voids in the oxide more efficiently and leads to less significant absorption shoulder than oxygen molecules. Also because the diffusion of water molecules in Ge is faster than in Si, less voids are formed and hence the absorption shoulder is less prominent in SiGe samples.