Contribution of Lifshitz-Van der Waals Interactions to the Surface Energy $\gamma^T$ of Si(100)-based Surfaces using the Van Oss-Young-Dupre Model

Surface energy $\gamma^T$ is studied via 3 Liquid Contact Angle Analysis (3LCAA) to optimize Wet NanoBonding$^\mathrm{TM}$, where surfaces hermetically cross-bond by anneal $<200^{\circ}$C. Applications lie in electronic sensors in saline environments. The Van Oss theory models interactions with dipoles (Lifshitz-Van der Waals) $\gamma^{LW}$, electron donors $\gamma^+$, and acceptors $\gamma^-$. Combining the equations of Van Oss and Young-Dupre yield the total $\gamma^T$ and its 3 components. Contact angles for 3 different liquids are measured with the sessile drop method on 4-8 drops per liquid for accuracy, in a Class 100 hood. Si wafers are studied after RCA clean or Herbots-Atluri (H-A) processing. After H-A, 2 sets are treated with Rapid Thermal Anneal or Oxidation (RTA or RTO). $\gamma^T$ is higher for the more defective, hydrophilic RCA cleaned Si ($47.3\pm 0.5 \frac{mJ}{m^2}$), while it is lower for the more ordered, hydrophobic H-A surfaces ($37.3\pm1.5 \frac{mJ}{m^2}$) and RTO ($34.5\pm 0.5 \frac{mJ}{m^2}$). In addition, $\gamma^{LW}$ interactions account for 90 to 98$\%$ of $\gamma^T$ in ordered oxides, unlike in hydrophilic surfaces (76.5$\%$). This indicates that 3LCAA can detect decreases in surface interaction from surface defects, impurities, and dangling bonds.