Measuring Surface Energies of GaAs (100) and Si (100) by Three Liquid Contact Angle Analysis (3LCAA) for Heterogeneous Nano-Bonding^TM

Analysis of the total surface energy γ^T and its three components as established by the van Oss-Chaudhury-Good Theory (vOCG) is conducted via Three Liquid Contact Angle Analysis (3LCAA). γ^T is correlated with the composition of the top monolayers (ML) obtained from High-Resolution Ion Beam Analysis (HR-IBA). Control of γ^T enables surface engineering for wafer bonding (Nano-Bonding^TM) and/or epitaxial growth. Native oxides on boron-doped p-Si(100) are found to average γ^T of 53 ± 1.4 mJ/m²) and are always hydrophilic. An HF in methanol or aqueous HF etch for 60 s always renders Si(100) hydrophobic. Its γ^T decreases by 20% to 44 ± 3 mJ/m² in HF in methanol etch and by 10% to 48 ± 3 mJ/m² in aqueous HF. On the contrary, GaAs(100) native oxides are found to always be hydrophobic. Tellurium n+-doped GaAs(100) yields an average of γ^T of 37 ± 2 mJ/m², 96% of which is due to the Lifshitz-Van der Waals molecular interactions (γ^LW = 36 ± 1 mJ/m²). However, hydrophobic GaAs(100) can be made highly hydrophilic. After etching, γ^T increases by almost 50% to 66 ± 1.4 mJ/m². 3LCAA shows that the γ^T increase is due to electron acceptor and donor interactions, while the Lifshitz-van der Waals energy γ^LW remains constant. IBA combining the 3.039 ± 0.01 MeV oxygen nuclear resonance with <111> channeling, shows that oxygen on Si(100) decreases by 10% after aqueous HF etching, from 13.3 ± 0.3 monolayers (ML) to 11.8 ± 0.4 ML 1 hour after etch.Te-doped GaAs(100) exhibits consistent oxygen coverage of 7.2 ± 1.4 ML, decreasing by 50% after etching to a highly hydrophilic surface with 3.6 ± 0.2 oxygen ML. IBA shows that etching does not modify the GaAs surface stoichiometry to within 1%. Combining 3LCAA with HR-IBA provides a quantitative metrology to measure how GaAs and Si surfaces can be altered to a different hydroaffinity and surface termination.