Spontaneous N Incorporation onto a Si(100) Surface

Initial nitridation of the Si(100) surface is investigated using photoemission, ion-scattering and ab initio calculations. After dissociation of NO or $\mathrm{N}{\mathrm{H}}_{\mathrm{3}}$, nitrogen atoms are found to spontaneously form a stable, highly coordinated $\mathrm{N}\mathrm{S}{\mathrm{i}}_{\mathrm{3}}$ species even at room temperature. The majority of the N species is incorporated into the subsurface Si layers occupying an interstitial site, whose atomic structure and unique bonding mechanism is clarified through ab initio calculations. This unusual adsorption behavior elucidates the atomistic mechanism of initial silicon nitride formation on the surface and has important implication on the N-rich layer formation at the ${\mathrm{S}\mathrm{i}\mathrm{O}}_x{\mathrm{N}}_y/\mathrm{S}\mathrm{i}$ interface.

Figure 1

N 1s photoemission spectra for (a) a standard oxynitride thin film (1.4 nm thick), (b) a Si(100) surface dosed with NO (100 L) at RT, (c) the surface as in (b) after an annealing at 950 K, (d) a ${\mathrm{N}\mathrm{H}}_3$-dosed Si(100) surface (100 L) annealed at (d) 550 K and at (e) 950 K. The spectra are taken at a photon energy ($h\nu$) of 500 eV. The reported energy for an $\mathrm{O}\mathrm{N}{\mathrm{S}\mathrm{i}}_2$ species is marked with a gray bar.

Figure 2

Medium-energy ion scattering spectrum (dots) of a Si(100) surface dosed with NO (100 L) at RT. The best-fit simulation is shown by the solid curve and the scattering energies of the Si, N, and O surface atoms are indicated by arrows. The inset shows the relative population of N and O atoms between different Si layers determined through the simulations.

Figure 3

(a) Top view of a Si(100) surface with a $c(4\times 4)$ unit cell (the large square) with various nitrogen adsorption sites considered. The side views of the two stable $\mathrm{N}{\mathrm{S}\mathrm{i}}_3$ configurations: (b) the HC configuration near the third-layer interstitial site and (c) the ${\mathrm{N}}_{\mathrm{s}\mathrm{u}\mathrm{b}}$ configuration with the down Si-dimer atom substituted by N. In (b) and (c), the bond lengths and angles are given in $\AA$ and degree, respectively.

Figure 4

Comparison of the energies calculated for various N configurations (TD and D for the surface adsorption and HC, HC1, HC2, HC3 for the subsurface interstitial incorporation) in terms of their depth from the surface Si layer (the first layer with “up” and “down” dimer atoms).