Reactions and diffusion of atomic and molecular oxygen in the $\mathrm{Si}{\mathrm{O}}_2$ network

To address the reactions and diffusion of atomic and molecular oxygen in $\mathrm{Si}{\mathrm{O}}_2$, the modification of the $\mathrm{Si}{\mathrm{O}}_2$ network on exposure to an atomic or molecular oxygen atmosphere is investigated by measuring the x-ray-diffraction profile of the residual order peak emanating from the oxide. Analyses of the peak intensity and its fringe pattern provide experimental evidence for the recent theoretical predictions, indicating that atomic oxygen is incorporated into the $\mathrm{Si}{\mathrm{O}}_2$ network near the surface and diffuses toward the interface along with modifying it even at a low temperature of $400°\mathrm{C}$, whereas molecular oxygen diffuses without reacting with the bulk $\mathrm{Si}{\mathrm{O}}_2$ even at a temperature of $850°\mathrm{C}$ that is sufficiently high for oxidation reaction at the interface.

Figure 1

X-ray-diffraction intensity profiles for the $\mathrm{O}\text{−}400°\mathrm{C}$ (circles), ${\mathrm{O}}_2\text{−}400°\mathrm{C}$ (triangles), and ${\mathrm{O}}_2\text{−}850°\mathrm{C}$ (squares) samples, coupled with the data for the base $\mathrm{Si}{\mathrm{O}}_2$ sample (filled circles). The intensity profiles are scanned along the CTR scattering extending from the 111 bulk Bragg peak and are plotted as a function of the $l$ value in a silicon reciprocal lattice unit. The solid lines are guides for the eyes.

Figure 2

Enlargement of the data in Fig. 1 for the $\mathrm{O}\text{−}400°\mathrm{C}$ (circles) and ${\mathrm{O}}_2\text{−}850°\mathrm{C}$ (squares) samples.

Figure 3

Schematic illustration of the positions of Si atoms in thermally grown $\mathrm{Si}{\mathrm{O}}_2$. The open circles represent Si atoms. The inside of the box is the substrate region. The small black dots show the positions of the expanded Si lattice in the absence of static disorder: (a) Model A: a homogeneous structure and (b) Model B: a gradually disordered structure.

Figure 4

X-ray-diffraction intensity profiles calculated for Model A and Model B in Fig. 5 on the basis of kinematical diffraction theory.

Figure 5

Side views of the model structures used for the calculation in Fig. 4, in [110] projection. Dark gray spheres represent Si atoms in the oxide region and light gray spheres represent Si atoms in the substrate region: (a) Model A: a homogeneous structure and (b) Model B: a gradually disordered structure.