First-principles calculations of Cu adsorption on an H-terminated Si surface

In this study, we use first-principles simulations to study the adsorption of copper onto H-terminated and partially OH-terminated silicon surfaces. We show that, in contrast to previous studies, copper adsorbs strongly to the H-terminated silicon surface and that the adsorption energy is significantly dependent on the local bonding environment. The addition of a hydroxide group increases the average adsorption energy while reducing the range of adsorption energies due to the strong interaction between copper and oxygen. Our results predict that copper will generally prefer to adsorb at dihydride sites on the surface, agreeing with experimental studies of copper nucleation. The adsorption energy hierarchy predicted by the calculations strongly supports the suggestion that copper acts as a micromask in wet chemical etching, blocking reactive sites.

Figure 1

(Color online) Side and overhead views of the atomic structure of a monohydride step. Silicon is represented by large yellow (large light gray) spheres, and hydrogen by small white spheres.

Figure 2

(Color online) Side and overhead views of the atomic structure of a horizontal dihydride step. Colors as in Fig. 1.

Figure 3

(Color online) Side and overhead views of the atomic structure of a vertical dihydride step. Colors as in Fig. 1.

Figure 4

(Color online) Overhead views of the atomic structure of (a) a kink in a horizontal dihydride step and (b) a kink in a monohydride step. Colors as in Fig. 1.

Figure 5

(Color online) Overhead and side views of the atomic structure of copper adsorbed at different sites on the surface. Silicon is represented by large yellow (large light gray) spheres, copper by small blue (dark gray) spheres, and hydrogen by small white spheres.

Figure 6

(Color online) Electron densities for different copper adsorption sites plotted from above at an isosurface of $0.019\mathrm{e}∕{\mathrm{\AA }}^3$.

Figure 7

(Color online) Overhead and side views of the atomic structure of copper adsorbed at OH-terminated A and F3 sites on the surface. Silicon is represented by large yellow (large light gray) spheres, copper by small blue (dark gray) spheres, hydrogen by small white spheres, and oxygen by the large red (black) spheres.

Figure 8

(Color online) (a) Structure of a $50\times 50{\mathrm{nm}}^2$ etched (100) silicon surface, adsorption energy profiles for the (b) H-terminated and (c) OH-terminated surfaces, (d) plot of the copper adsorption energy across the surface for hydrogen termination, and (e) plot of the copper adsorption energy across the surface for hydroxyl termination. The dashed lines in (d) and (e) mark the path of the energy profiles.