5:00 PM - EP10.03.06
Understanding the Modification of Oxidation States in GaAs Surface by Etching Using XPS, IBA and 3LCAA
Amber Chow1,2,Sukesh Ram1,2,3,Shaurya Khanna1,2,Nikhil Suresh1,2,3,Saaketh Narayan1,2,3,Brian Baker1,2,3,Francesca Ark1,2,Jack Day1,2,3,Nicole Herbots1,2,3,Karen Kavanagh4,Timmothy Karcher1,Robert Culbertson1,Shawn Whaley1,2
Arizona State University1,SiO2 Innovates LLC2,AccuAngle Analytics LLC3,Simon Fraser University4
Native oxides used as protective passivation layers on semiconductors, inhibit high quality epitaxial growth, increase contact resistance, and decrease reliability of measurements. For opto-electronics, a better understanding of native oxides and their removal is needed for heterovalent integration of semiconductors. In this work, the surface energies, the oxygen areal coverage, and the oxidation states of Te-doped n+ GaAs(100) and B-doped p- Si(100) surfaces are investigated before and after wet chemical etching in order to bond Ga and Si via NanoBondingTM. Heterovalent integration via NanoBondingTM consists of direct bonding between two surfaces using surface engineering where both surfaces’ hydro-affinity are reversed from hydrophobic to hydrophilic, and vice-versa. Surface Processing modifies electron donor/acceptor interactions, increasing electron exchange via precursor phases. This catalyzes cross-bonding between both etched surfaces.
The van Oss-Chaudhury-Good (vOCG) theory computes the surface energy, γT, of semiconductors from its three components via Three Liquid Contact Angle Analysis (3LCAA), combining molecular interactions or “Lifshitz-Van der Waals” energy, γLW, with energy of interaction of electron donors, γ+, and acceptors, γ-. The image analysis algorithm “Drop and Reflection Operative ProgramTM” (DROPTM) enables fast and accurate extraction of contact angles without subjectivity, reducing the typical ~5° error in manually extracted contact angles to < 1° . With multi-angle data, DROPTM yields γT within 3%. 3LCAA determines the effects of etching on hydro-affinity and oxidation states and is correlated with compositional changes.
Before etching, GaAs(100) is initially hydrophobic with γT of 33 ± 1 mJ/m2, whether for doped or semi-insulating GaAs. After etching , γT increases by a factor of two or 100% to 66 ± 1 mJ/m2, making etched GaAs highly hydrophilic. Hydro-affinity and reactivity are modified by increasing electron donor/acceptor interactions by a factor of three to ten while γLW increases by at most 50%.
High Resolution Ion Beam Analysis (HR-IBA) combines <111> channeling with 3.039 ± 0.01 MeV (16O, 16O) nuclear resonance. Ga, As, and O coverage are measured to within ± 0.2 monolayer (ML) before and after etching by matching SIMNRA simulations to HR-IBA spectra . IBA shows that after the etch, oxygen coverage on GaAs decreases 50 ± 4% from 7.2 ± 0.2 ML to 3.6 ± 0.2 ML. The 53:47 stoichiometric ratio of Ga to As remains constant after etching within ± 1%. The areal surface density shows that decreasing oxygen coverage by a factor two is commensurate with decreasing displacement of Ga and As surface atoms, implicating etching doesn’t corrode GaAs or alter stoichiometry.
X-Ray Photoelectron Spectroscopy (XPS) measured oxidation states and uniformity of the surface for C, O, Ga, and As on two locations of two wafers for both native oxide and etched GaAs(100). GaAs native oxides include binary oxides (Ga2O3, As2O3, As3O5), ternary oxides (GaAsO4), and metallic arsenic. The proportion of oxidized Ga increased from 40 ± 1% to 47 ± 1% while the proportion of oxidized As decreased from 21 ± 1% to 19 ± 1%. This change in As oxidation reverses the hydro-affinity of GaAs(100) as the decrease in fully oxidized As increases the amount of unfilled bonds of As, increasing γT.
In summary, 3LCAA measured a change in GaAs hydro-affinity before and after etching by a factor of two from strongly hydrophobic (γT = 33 ± 1 mJ/m2) to strongly hydrophilic (γT = 66 ± 1 mJ/m2). HR-IBA accurately determined to within 0.2 ML decreased oxygen coverage and stoichiometry as a function of wet chemical etching. XPS was then correlated with IBA to establish modifications in the proportion of oxidized Ga and As atoms and in their oxidation states. Modification of oxidation states help explain the dramatic change observed in hydro-affinity.
 US Patents #9,018,077; #9,589,801, Herbots N. et al (2015); (2017)