title: Lateral Ge Diffusion During Oxidation of Si/SiGe Fins.
abstract: This Letter reports on the unusual diffusion behavior of Ge during oxidation of a multilayer Si/SiGe fin. It is observed that oxidation surprisingly results in the formation of vertically stacked Si nanowires encapsulated in defect free epitaxial strained SixGe1-x. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) shows that extremely enhanced diffusion of Ge occurs along the vertical Si/SiO2oxidizing interface and is responsible for the encapsulation process. Further oxidation fully encapsulates the Si layers in defect free single crystal SixGe1-x(x up to 0.53), which results in Si nanowires with up to -2% strain. Atom probe tomography reconstructions demonstrate that the resultant nanowires run the length of the fin. We found that the oxidation temperature plays a significant role in the formation of the Si nanowires. In the process range of 800-900 °C, pure strained and rounded Si nanowires down to 2 nm in diameter can be fabricated. At lower temperatures, the Ge diffusion along the oxidizing Si/SiO2interface is slow, and rounding of the nanowire does not occur, while at higher temperatures, the diffusivity of Ge into Si is sufficient to result in dilution of the pure Si nanowire with Ge. The use of highly selective etchants to remove the SiGe could provide a new pathway for the creation of highly controlled vertically stacked nanowires for gate all around transistors.
authors.affiliation: Department of Materials Science and Engineering, University of Florida , Gainesville, Florida 32611, United States.
authors.forename: William M
authors.identifier: 0000-0002-1255-310X
authors.initials: WM
authors.lastname: Brewer
authors.affiliation: National High Magnetic Field Laboratory, Florida State University , Tallahassee, Florida 32310, United States.
authors.forename: Yan
authors.initials: Y
authors.lastname: Xin
authors.affiliation: Applied Materials, Gloucester, Massachusetts 01930, United States.
authors.forename: C
authors.initials: C
authors.lastname: Hatem
authors.affiliation: Department of Metallurgical and Materials Engineering, Colorado School of Mines , Golden, Colorado 80401, United States.
authors.forename: D
authors.initials: D
authors.lastname: Diercks
authors.affiliation: Department of Materials Science and Engineering, University of Florida , Gainesville, Florida 32611, United States.
authors.forename: V Q
authors.initials: VQ
authors.lastname: Truong
authors.affiliation: Department of Materials Science and Engineering, University of Florida , Gainesville, Florida 32611, United States.
authors.forename: K S
authors.initials: KS
authors.lastname: Jones
keywords: Ge condensation; SiGe oxidation; gate all around transistor (GAA); interfacial diffusion; lateral diffusion; silicon nanowire