Understanding gaas Native Oxides By Correlating Three Liquid Contact Angle Analysis (3LCAA) and High Resolution Ion Beam Analysis (HR-IBA) to X-Ray Photoelectron Spectroscopy (XPS) as Function of Surface Processing

Abstract

Chemical bonding in native oxides of GaAs, before and after etching, is detected by X-Ray Photoelectron Spectroscopy (XPS). It is correlated with surface energy engineering (SEE), measured via Three Liquid Contact Angle Analysis (3LCAA), and oxygen coverage, measured by High Resolution Ion Beam Analysis (HR-IBA).Before etching, GaAs native oxides are found to be hydrophobic with an average surface energy, γT, of 33 ± 1 mJ/m2, as measured by 3LCAA. After dilute NH4OH etching, GaAs becomes highly hydrophilic and its surface energy, γT, increases by a factor 2 to a reproducible value of 66 ± 1 mJ/m2. Using HR-IBA, oxygen coverage on GaAs is found to decrease from 7.2 ± 0.5 monolayers (ML) to 3.6 ± 0.5 ML. The 1.17 ratio of Ga to As, measured by HR-IBA, remains constant after etching.XPS is used to measure oxidation of Ga and As, as well as surface stoichiometry on two locations of several GaAs(100) wafers before and after etching. The relative proportions of Ga and As are unaffected by adventitious carbon contamination. The 1.16 Ga:As ratio, measured by XPS, matches HR-IBA analysis. The proportions of oxidized Ga and As do not change significantly after etching. However, the initial ratio of As2O5 to As2O3, within the oxidized As, significantly decreases after etching from approximately 3:1 to 3:2.Absolute oxygen coverage, as a function of surface processing, is determined within 0.5 ML by HR-IBA. XPS offers insight into these modifications by detecting electronic states and phase composition changes of GaAs oxides. The changes in surface chemistry are correlated to changes in hydro-affinity and surface energies measured by 3LCAA.

GaAs to Si Direct Wafer Bonding at T ≤ 220°C in Ambient Air via Nano-BondingTM and Surface Energy Engineering (SEE)

“…NB is a new DWB process at T ≤ 220°C [9,18,19,[23][24][25]. NB uses SEE to cross-bond wafers at the nanoscale and 2D-PP to modify γ T0 and H-A 0 by bringing each surface in the wafer pair to synergistic 'farfrom-equilibrium' states [14,15,17,24,26].…”

“…They are characterized by 3LCAA, then a few 7 mm x 7 mm squares pieces for conducting HR-IBA and a few 10 mm x 10 mm square pieces for XPS. Wafers 3 The vOCG theory was proposed in 1989 as a three-component theory for γ T [9,18,19,[23][24][25]27]. The theory states in Eq.…”

“…The model for this work's approach is low temperature NB, which can lower thermal budgets for DWB to ≤ 220°C and wafer pair compression to P ≤ 60 kPa (9 psi). NB lowers thermal budget via Room Temperature Surface Energy Engineering (SEE) for compound semiconductors [9,18,19,[23][24][25]. SEE modi es initial total surface energies, γ T0 , to far-from-equilibrium states, γ T *, so direct cross-bonds between two different crystals can occur via direct donor-acceptor interactions between SEE-modi ed surfaces.…”

“…Measuring water contact angles to ± 1° makes possible precise characterizations of hydro-a nities as well. Four data points are collected on two different samples cut from GaAs wafers before and after SEE to establish reproducibility [23].…”

“…Thus, HR-IBA shows that SEE decreases oxygen coverage on GaAs by 50%. Critically, the Ga:As ratio does not change after etching[23,29]. The 50% decrease in O detected by HR-IBA affects primarily the oxidation states of Arsenic.…”