## 3 Results
However, just as the concentration of molecules at the surface cannot be directly inferred from that of the solution, the pH at the bonding interface (if such a concept is meaningful) cannot be straightforwardly deduced from the pH of the spreading solution. Furthermore, knowing the molecular concentration at the surface provides limited insight, as the amount of water at the bonding interface depends on numerous factors, making it difficult to estimate an \"interfacial pH\" value. Indeed, firstly, the humidity of the bonding atmosphere affects the amount of water adsorbed on the surfaces. Additionally, the propagation of the bonding wave itself could alter the water content at the interface. For example, gas compression between wafers during bonding increases its temperature, influencing the equilibrium between the surface and the atmosphere. It is the opposite of the edge bonding void generation mechanism, which is driven by gas decompression, lowering the temperature and causing water droplet condensation at the wafer edges [46; 47; 48]. The compression associated with bonding wave propagation explains why using dry gases like nitrogen or argon alone is insufficient to \begin{table}
\begin{tabular}{c c} \hline \hline
**Dispense Solution** & **DEAE Concentration on Wafer Surface (molecule/cm\({}^{2}\))** \\ \hline H\({}_{2}\)O & ND \\ DEAE \(10^{-6}\) g/cm\({}^{3}\) & ND \\ DEAE \(10^{-5}\) g/cm\({}^{3}\) & \(9.74\times 10^{12}\) \\ DEAE \(10^{-4}\) g/cm\({}^{3}\) & \(8.14\times 10^{13}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: DEAE concentration on wafer surfaces measured by WOS/ATDGCMS. \begin{table}
\begin{tabular}{c c} \hline \hline
**Dispense Solution** & **Na\({}^{+}\) Concentration on Wafer Surface (at/cm\({}^{2}\))** \\ \hline H\({}_{2}\)O & \textless{}2 \(\times\) 10\({}^{11}\) \\ NaOH \(10^{-8}\) g/cm\({}^{3}\) & \textless{}2 \(\times\) 10\({}^{11}\) \\ NaOH \(10^{-7}\) g/cm\({}^{3}\) & \(2.8\times 10^{11}\) \\ NaOH \(10^{-6}\) g/cm\({}^{3}\) & \(1.8\times 10^{12}\) \\ NaOH \(10^{-5}\) g/cm\({}^{3}\) & \(1.2\times 10^{13}\) \\ NaOH \(10^{-4}\) g/cm\({}^{3}\) & \(8.4\times 10^{13}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Na\({}^{+}\) concentrations on wafer surfaces from TXRF. 2 \(\times\) 10\({}^{11}\) at/cm\({}^{2}\) is the TXRF detection limit for Na\({}^{+}\). prevent voids [46], as these gases can remove water from the wafer surface. Moreover, the water quantity at the interface may vary during the queue time before annealing. As demonstrated by [PERSON] et al. [44], the water content at a hydrophilic silicon dioxide bonding interface can range from 1.6 to 3.4 monolayers, partially filling surface roughness gaps. Given these complexities, it is difficult to determine the exact water content at the bonding interface, which is thus challenging to calculate concentrations. Additionally, at an interface width of only 1 nm, water ceases to behave like a liquid and exhibits properties more akin to ice, significantly reducing atomic mobility. Even if the concentration, acid-base equilibrium, and pH value could be determined, their physical interpretation under such interfacial confinement would differ markedly from conventional conditions. Therefore, focusing on the quantity of molecules may offer more practical and meaningful insights.