Paper SE+2D+EM-WeA3
Cross-Bonding between Silicon, Silica and III-V Surfaces at the Nano-Scale Using Energy Analysis via Three Liquid Contact Angle Analysis (3LCAA) to achieve Hermetic Wet NanoBonding™

Wednesday, November 9, 2016, 3:00 pm, Room 101D

Mobile ions such as Na, percolate from saline environments into marine and atmospheric sensors and limit their reliability to less than a week. Implantable glucose monitors for diabetics require replacement about every 3-7 days, with finger blood samples re-calibration daily. Hermetic bonding can yield economic, medical, and human benefits by extending lifetime of such integrated sensors from days to years. Si-based surfaces such as thermally-grown amorphous a-SiO₂ on Si(100), and on III-V surfaces can be hermetically bonded with Wet NanoBonding™ to yield dense, hermetic cross-bonding. In Wet Nonbonding™, planarization is first accomplished at the nano-scale, then a-SiO₂ is etched with HF, while a 2 nm precursor β-cSi₂O₄H₄ phase is grown on Si(100) to initiate cross-bonding. Next, both surfaces are put into mechanical contact in a class 10 clean-room and nano-bonded under low temperature (T<180° C) steam pressurization.

Modifying the surface energy components of 2 surfaces can help optimize hermerticity by increasing the density of cross-bonding. Surface energy γ^T can be measured via 3 Liquid Contact Angle Analysis (3LCAA) using the the Van-Oss theory, which models γ^T for semiconductor and insulators in 3 interactions : (1) Lifschitz-Van der Waals molecular dipole interactions γ^LW, (2) electron donor interactions γ⁺, and (3) electron acceptor interactions γ⁻. Successful NanoBonding™ can occur between one surface with high γ⁺ and one with high γ⁻. 3LCAA extracts these from contact angles between several liquids with known surface energies and the surface. Sessile drop analysis with water, glycerin, and α-bromonaphthalene is conducted in a Class 100 hood using 4-8 drops per liquid for statistical accuracy. RCA cleaned Si(100) and Si(100) terminated with 2-nm β-cSi₂O₄H₄ via the Herbots-Atluri (H-A) process are used, in combination with Rapid Thermal Anneal and Oxidation (RTA and RTO), to grow a-SiO₂ [3]. The γ^T of hydrophilic RCA-cleaned Si(100) is 47.3±0.5 mJ/m² , 25% higher than the γ^T of ordered, hydrophobic β-cSi₂O₄H₄ Si(100) , 37.3±1.5mJ/m², and 30% higher than RTO oxides 34.5±0.5 mJ/m². Interactions from γ^LW account for 90-98±2% of γ^T in ordered oxides, but only 76.5±2.0% of those in hydrophilic surfaces. Thus, 3LCAA detects changes in surface reactivity from defects, impurities, and dangling bonds. While γ⁺ accounts for little to none of γ^T for all but one surface, 180° C annealing during Wet NanoBonding significantly increases γ⁺ in β-cSiO₂. Conversely, HF etching significantly increases γ⁻ for a-SiO₂. When matching acceptor with donor interactions between surfaces via 3LCAA, cross-bonding density appears to increase, and NanoBonding™