Structure and epitaxy studies of cobalt silicide/silicon heterostructures
Zaluzec, Matthew John
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Permalink
https://hdl.handle.net/2142/21033
Description
Title
Structure and epitaxy studies of cobalt silicide/silicon heterostructures
Author(s)
Zaluzec, Matthew John
Issue Date
1991
Doctoral Committee Chair(s)
Rigsbee, J. Michael
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Engineering, Metallurgy
Engineering, Materials Science
Language
eng
Abstract
When considering transition metal silicides for use in integrated circuit technology, CoSi$\sb2$ stands out as a silicide possessing an excellent combination of properties. These include, low resistivity (15-25 $\mu$ohm-cm), reproducible Schottky barrier heights (0.43 eV and 0.65 eV) on both p and n-type silicon respectively, and most notably the ability to grow epitaxially on Si(111). However, this silicide suffers the detrimental effects of CoSi$\sb2$ pinhole formation seriously restricting the applicability of this silicide system.
This investigation examines the structure/processing/property relationship of thin film cobalt silicide/silicon heterostructures grown on Si(111). The two primary objectives of this research are: (1) identify the basic mechanisms associated with pinhole formation and cobalt silicide thin film growth; and (2) characterization of cobalt silicides grown by Si$\sb{\rm a}$/Co/Si$\sb{\rm c}$ multilayer deposition and reaction and the effect this deposition technique has on the microstructure of cobalt silicide thin films. Thin film deposition and silicide phase formation was carried out in an ultra high vacuum environment using electron beam evaporation and in-situ reaction annealing. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been used to characterize the microstructure and identify the onset of pinhole formation during cobalt silicide thin film growth. Auger electron spectroscopy (AES), and secondary ion mass spectroscopy (SIMS) have been used to determine depth compositional data and impurity content across the silicide/silicon interface. X-ray diffraction (XRD) was used for silicide phase identification and to determine the relative crystalline quality of the epitaxial silicide layers.
Interfacial pinhole formation was identified at the CoSi/Si interface and involves several active mechanisms which include locally enhanced silicon and cobalt diffusion, silicide spike formation during CoSi thin film growth, and volumetric contractions during the CoSi $\to$ CoSi$\sb2$ phase transformation. Multilayer Si$\sb{\rm a}$/Co/Si$\sb{\rm c}$ thin film deposition is an effective processing technique for controlling microstructure and preventing pinhole formation by promoting uniform interfacial silicide growth. Epitaxial pinhole free CoSi$\sb2$ films were grown by single step annealing Si$\sb{\rm a}$/Co/Si$\sb{\rm c}$ multilayer structures. Two step annealing Si$\sb{\rm a}$/Co/Si$\sb{\rm c}$ multilayer thin films results in polycrystalline CoSi$\sb2$.
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