Metrology of very thin silicon epitaxial films

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.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Materials Science and Engineering

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

1998

Author dc:creator

• Chen, Weize, 1966-

Advisor dc:contributor.advisor

• L. Rafael Reif and Lionel C. Kimerling.

• Materials Science and Engineering

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/17469

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/17469