Kinetic mechanisms of the [ital C]49-to-[ital C]54 polymorphic transformation in titanium disilicide thin films: A microstructure-scaled nucleation-mode transition

Journal Article · Sun May 15 00:00:00 EDT 1994 · Physical Review, B: Condensed Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.49.13501· OSTI ID:6622371

Ma, Z; Allen, L H ^[1]

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1. Department of Materials Science and Engineering and Coordinated Science Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

Kinetics and mechanism of polymorphic transformation in TiSi[sub 2] thin films from a base-centered orthorhombic structure ([ital C]49-TiSi[sub 2]) to a face-centered orthorhombic structure ([ital C]54-TiSi[sub 2]) were investigated with emphasis on effect of film thickness scaling on phase transition using [ital in] [ital situ] resistance measurements, XRD, and TEM. [ital C]49 disilicide films of different thicknesses were prepared by annealing Ti/polycrystalline Si thin film couples of varying Ti thicknesses (250, 550, and 1000 A). Transformation rate was found to be a strong function of film thickness and temperature, and can be described by [tau][proportional to]exp([ital E][sub [ital a]]/[ital kT]) with an activation energy of 3.73, 4.44, and 5.08 [+-]0.07 eV for 1000, 550, and 250 A Ti, respectively. An unusual transition between nucleation sites was observed as a result of the scaling: for samples with 250 A Ti, the transformation proceeded by nucleating the [ital C]54 polymorph at grain edges (three-grain junctions) of the [ital C]49-TiSi[sub 2] films while the [ital C]54 nuclei were predominantly formed at the grain boundaries (two-grain junctions) in thicker films, which are in good agreement with predictions of the nucleation mode from kinetics analyses. It has been suggested that the nucleation of the [ital C]54-TiSi[sub 2] is likely to be the rate-limiting step in the overall transformation. Based on microstructural evidences provided by TEM, the significance of these observations due to reduction in film thickness was discussed by considering energetics of nucleation at different geometrical sites, nucleation site density, and effects of surface and stress. It was demonstrated that the surface contribution and nucleation site density become important for nucleation in thinner films with largely increased surface-to-volume ratio...

• OSTI ID: 6622371
• Journal Information: Physical Review, B: Condensed Matter; (United States), Vol. 49:19; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
TITANIUM SILICIDES
CRYSTAL-PHASE TRANSFORMATIONS
THIN FILMS
ELECTRIC CONDUCTIVITY
KINETICS
MICROSTRUCTURE
NUCLEATION
ORTHORHOMBIC LATTICES
TEMPERATURE RANGE 0400-1000 K
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
ELECTRICAL PROPERTIES
ELECTRON MICROSCOPY
FILMS
MICROSCOPY
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SCATTERING
SILICIDES
SILICON COMPOUNDS
TEMPERATURE RANGE
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
360202* - Ceramics
Cermets
& Refractories- Structure & Phase Studies