| AVS 65th International Symposium & Exhibition | |
| Surface Science Division | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Division Poster Session |
| Presenter: | Saaketh Narayan, Arizona State University |
| Authors: | S.R. Narayan, Arizona State University J.M. Day, Arizona State University N. Herbots, Arizona State University A. Brimhall, Arizona State University A. Mascareno, Arizona State University A. Krishnan, Harvard University S.D. Whaley, Arizona State University R.B. Bennett-Kennett, Stanford University K.L. Kavanagh, Simon Fraser University, Canada |
| Correspondent: | Click to Email |
Processing modifies hydroaffinity, reactivity, and total surface energy, γT, of semiconductor oxides. Si(100) and its oxides are studied, including native oxides, conventional thermal SiO2, Rapid Thermal Oxides (RTO), Rapid Thermal Annealed (RTA) oxides, RCA processed Si, Herbots-Atluri (HA) passivated [1] Si, alpha-quartz SiO2, and oxides after HF-based etching. Correlating surface energies of Si(100) and SiO2 to composition and processing can reproducibly establish the metrology needed for wafer bonding. Cross-bonding is key in bonding conducted at T < 220°C, or NanoBondingTM, [2,3] for Si(100) to SiO2, GaAs(100), and LiTaO3. Si(100) and Si(111) samples investigated include B-doped p- and p+ wafers, and P-doped n- and n+ wafers.
The surface energy of 50 wafers is measured via Three Liquid Contact Angle Analysis (3LCAA) using the van Oss-Chaudhury-Good (vOCG) model for semiconductors and insulators. The γT includes Lifshitz-van der Waals interaction, γLW, interaction with electron donors, γ+, and with acceptors, γ-. Reproducibility of contact angle measurements to extract γT, γLW, γ+, and γ- is achieved by metering µL droplets of 18 MΩ deionized H2O, glycerin, and α-bromonaphthalene in a class 100/ISO 4 laminar flow hood. 4 contact angles are extracted from each droplet and its reflection through 18 MP images analyzed automatically via the Drop and Reflection Operative Program (DROP) which removes subjectivity and speeds up analysis. 30 droplets yield 120 angles, with an accuracy of 3%.
MeV Ion Beam Analysis (IBA) combining <111> channeling with nuclear resonance yields 16O coverage, which is then correlated to γT, γLW, γ+, and γ-. Native oxides on p- Si are always hydrophilic, with a γT of 53 ± 2 mJ/m2. RCA wafers have a lower γT of 47.3 ± 0.5 mJ/m2, as RCA removes impurities, but are still relatively hydrophilic. Next, RTA oxides exhibit a lower γT than RCA oxides, as thicker oxides are more hydrophobic, corroborated by higher 16O coverage. H-A wafers have a lower 16O coverage but also a more hydrophobic γT of 37.3 ± 1 mJ/m2, being terminated with ordered Si2O4H4. RTO on H-A wafers yields the most hydrophobic surfaces with γT = 34.5 ± 0.5 mJ/m2. IBA on native oxides of p- Si detects 13.3 ± 0.3 16O ML, while IBA on H-A and HF etched Si detects 11.8 ± 0.4 16O ML. IBA on RTA and RTO oxides show that thicker oxides yield more hydrophobic surfaces. In summary, 3LCAA in conjunction with IBA yields new insights in the relationship between γT, oxygen coverage, and processing.[1] Herbots N. et al, US Pat N° 6613677 (2003), 7,851,365 (2010).
[2] Herbots, N. et al, US Pat. N° 9,018,077 (2015) 9,589,801 (2017)
[3] Herbots N., Islam R., US Pat. Pend. (2018)