| AVS 65th International Symposium & Exhibition | |
| Applied Surface Science Division | Thursday Sessions |
| Session AS+SE-ThM |
| Session: | Applied Surface Analysis of Novel, Complex or Challenging Materials |
| Presenter: | Sukesh Ram, Arizona State University |
| Authors: | S. Ram, Arizona State University K.L. Kavanagh, Simon Fraser University, Canada F.J. Ark, Arizona State University C.E. Cornejo, Arizona State University T.C. Diaz, Arizona State University M.E. Bertram, Arizona State University S.R. Narayan, Arizona State University J.M. Day, Arizona State University M. Mangus, Arizona State University R.J. Culbertson, Arizona State University N. Herbots, Arizona State University R. Islam, Cactus Materials, Inc. |
| Correspondent: | Click to Email |
Native oxides used as surface passivation during semiconductor processing hinder the formation of high quality epitaxial layers. In this research, the surface energies and oxygen content of native oxides of Si(100) and GaAs(100) are measured before and after surface processing prior to a wafer bonding process at T<220°C, “NanoBonding™” [1,2]. Based on Van Oss’s theory, Three Liquid Contact Angle Analysis (3LCAA) yields the total surface energy, yT, of semiconductors and insulators. Van Oss models yT as combining of molecular interactions or “Lifshitz-Van der Waals” energy yLW with the energy of interaction with electron donors, y+,and acceptors, y-. A new automated image analysis algorithm, “Drop and Reflection Operative Program”(DROP), enables fast, accurate and reproducible extraction of contact angles without subjectivity, reducing to <1° the typical ~5° error between contact angles measurements due to manual extraction. Using for each wafer, a minimum of 12 to 30 drops yields 48 to 120 contact angles, yielding yT , yLW, y+ and y- with accuracies better than 3%. By using Ion Beam Analysis (IBA) combining <111> channeling in (100) crystals with the 3.039 ± 0.01 MeV (16O, 16O) nuclear resonance, oxygen coverage can be measured with ML accuracy before and after processin, via SIMNRA simulations, correlating oxygen coverage to data within 1%.
Boron-doped p-Si(100) is found to be always hydrophilic pre-etch, with a yT of 53 ± 1.4 mJ/m2. After an aqueous HF (1:20) etch, yT decreases 10% to 48 ± 2.6 mJ/m2, and Si is hydrophobic. GaAs(100) is initially always very hydrophobic with a yT of 37 ± 2.0 mJ/m2. After etching, Te-doped n+GaAs always becomes hydrophilic with a yT increase of 50% to 66 mJ/m2 ± 1.4 mJ/m2. Native oxides on B-doped p-Si(100) wafers are found by IBA to contain 13.3 x 1015 at/cm2 or 13.3 ± 0.3 oxygen monolayers (ML). After an aqueous HF (1:20) etch, Si(100) exhibits only a 11.6 ± 3% reduction in oxygen to 11.8 ± 0.4 ML . GaAs native oxides contain 7.2 ± 1.4 oxygen ML. After a proprietary passivation-based etch, GaAs native oxides are reduced 49.1 ± 4% to 3.6 ± 0.2 oxygen ML without change in GaAs surface stoichiometry.
3LCAA can quantify accurately the reactivity of a surface before Nano-BondingTM, which can be correlated to oxygen coverage and structure. High-resolution IBA and 3LCAA allows for a quantitative analysis of Si and GaAs surfaces energies as function of surface processing, enabling for the engineer interactions between surfaces for NanoBonding.
1. Herbots N. et al. US Pat. No 9,018,077 (2015), US Pat. No 9,018,077 (2017)
2. Herbots N., Islam R., US Pat. Pending (2018), filed March 18, 2018