Theoretical study of the mechanism of dry oxidation of $4H$-SiC

Possible defect structures, arising from the interaction of ${\mathrm{O}}_2$ molecules with an ideal portion of the $\mathrm{SiC}∕\mathrm{Si}{\mathrm{O}}_2$ interface, have been investigated systematically using density functional theory. Based on the calculated total energies and assuming thermal quasiequilibrium during oxidation, the most likely routes leading to complete oxidation have been determined. The defect structures produced along these routes will remain at the interface in significant concentration when stopping the oxidation process. The results obtained for their properties are well supported by experimental findings about the $\mathrm{SiC}∕\mathrm{Si}{\mathrm{O}}_2$ interface. It is found that carbon-carbon bonds can explain most of the observed interface states but not the high density near the conduction band of $4H$-SiC.

Figure 1

Schematic overview of the experimental data about the $D_{it}$ at the $4H\text{−}\mathrm{SiC}∕\mathrm{Si}{\mathrm{O}}_2$ interface, after Ref. 1. For explanation, see the text.

Figure 2

(Color online) The interface model [O, small, dark grey (red) spheres; C, medium sized black spheres; Si, large, light grey (yellow) spheres, H, small light grey spheres].

Figure 3

(Color online) The most important interface defects, viewed nearly parallel to the interface, $\mathrm{Si}{\mathrm{O}}_2$ on top. [O, small, dark grey spheres (red) C, medium sized black spheres; Si, large, light grey spheres (yellow) defect atoms are marked by large spheres.]

Figure 4

(Color online) ${\left({\mathrm{C}}_{\mathbf{i}}\right)}_2$ carbon diinterstitial at the interface, viewed nearly parallel to the SiC surface, $\mathrm{Si}{\mathrm{O}}_2$ on top. [O, small, dark grey spheres (red); C, medium sized black spheres; Si, large, light grey spheres (yellow); defect atoms are marked by large spheres.] The oxygen neighbors of the upper front silicon atoms have been removed from the picture for clarity.

Figure 5

(Color online) The SiC dry oxidation reaction scheme. Positive energies indicate exother- mic reactions between initial defects of the interface (rectangular frames) and incoming ${\mathrm{O}}_2$ molecules (round frames) at the beginning of the arrows. The resulting defects (and possible CO molecules) are at the end of the arrow(s) near which the reaction energy is shown. [Equations (2, 3, 4, 5, 6, 7, 8) were extracted this way from the figure.] The dominant reaction paths are marked by thick lines (green and red).

Figure 6

Environment dependent range of energy levels of the elementary C-C units compared to the observed $D_{it}$ (cf. Introduction) of $4H$-SiC.

Figure 7

(Color online) ${\left({\mathrm{C}}_3\right)}_{\mathrm{Si}}$ carbon aggregates at the interface, (a) obe unit viewed nearly parallel to the SiC surface, (b) top view of the interface layer with three neighboring units. [O, small, dark grey spheres (red) C, medium sized black spheres; Si, large, light grey spheres (yellow) defect atoms are marked by large spheres.]