Metrology of very thin silicon epitaxial films
Name
42077708-MIT.pdf
Description
Full printable version
Size
8.09 MB
Format
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Checksum (MD5)
40eeef74fce951bbbdef843c115bc35f
Author(s)
Chen, Weize, 1966-
Advisor(s)
L. Rafael Reif and Lionel C. Kimerling.
Date Issued
1998
Publisher
Massachusetts Institute of Technology
Abstract
In this thesis, non-destructive thickness measurement of sub-0.5 µm silicon epitaxial films has been successfully performed using spectroscopic ellipsometry (SE) in the visible to near infrared (NIR) range (0.73 - 3.3 eV). The undoped epitaxial .films are grown on heavily doped substrates by chemical vapor deposition at 700 - 900° C. The effect of heavy doping on the optical properties of crystalline silicon in the spectral range 0.73 - 3.3 eV is precisely described by the Drude free carrier model. It is shown that visible-NIR SE can simultaneously determine the substrate dopant concentration, the thicknesses of epitaxial film and native oxide, and if present, the thickness of the transition layer between the epitaxial film and the substrate. The epitaxial film thicknesses measured by visible-NIR SE are in excellent agreement with results of secondary ion mass spectrometry (SIMS). The substrate dopant concentrations measured by SE also agree well with SIMS results for n-type substrates, but are consistently higher than SIMS values for p-type substrates. It is also demonstrated that visible-NIR SE is very sensitive to the epi/substrate interface quality therefore can be used for process monitoring in low temperature silicon epitaxy. Non-destructive determination of thickness and composition of strained Si1-xGex (0 < x 0.30) heteroepitaxial layers has also been successfully carried out in this thesis using visible-NIR SE. The dielectric function of the Sii-xGex layers in the spectral range 0. 75 - 2. 75 e V is fitted to a self-consistent empirical formula with only five fitting parameters. Accurate ellipsometry measurement of thickness and composition is successfully demonstrated using this formula. This thesis has developed a non-destructive technique for the measurement of both silicon and Sii-xGex epitaxial films. This technique is suitable and can be easily implemented for in-line, in situ and real-time measurement. This study also provides a numerical expression for the optical constants of strained Si1-xGex in the spectral range of interest for most optoelectronic applications.
Description
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.
Includes bibliographical references (p. 161-169).
Subjects
Materials Science and Engineering
MIT Department
Massachusetts Institute of Technology. Department of Materials Science and Engineering
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