Reminder: University Oral Examination - Daniel B. Aubertine (Nov. 25, 10AM)

Dan Aubertine auber at stanford.edu
Mon Nov 24 16:07:29 PST 2003


University Oral Examination
Daniel B. Aubertine
Department of Materials Science and Engineering

Tuesday, November 25, 2003
10:00AM (Refreshments will be served at 9:45AM)
335 McCullough Building
Stanford University

An x-ray diffraction study of concentration and strain dependent Si/SiGe 
interdiffusion

SiGe alloys have become important materials for semiconductor device 
engineering.  They provide a means of tailoring the properties of the 
semiconductor, such as band-gap, carrier mobility, and dopant solubility, 
at specific locations within a device.  CVD growth rates for single crystal 
SiGe are also much faster than for Si, allowing improved throughput and 
decreased contamination.  Further, all of these benefits are realized at a 
relatively low cost owing to the high degree of compatibility between SiGe 
and Si processing technologies.

As SiGe films are introduced into deeply scaled, ultra-fast MOS devices, it 
is increasingly clear that interdiffusion at Si/SiGe interfaces is a 
significant problem.  Strained Si MOSFETs typically utilize a thin, 
epitaxial, strained Si channel grown onto a relaxed SiGe layer.  For these 
structures, out-diffusion of Ge from the SiGe layer into the Si channel is 
a factor limiting the practical thermal exposure during 
processing.  Predicting the degree of intermixing is difficult because the 
interdiffusion process is influenced by the local Ge concentration, film 
strain, and non-equilibrium point defect concentrations. Development of a 
robust model for Si/SiGe interdiffusion requires that each of these effects 
be isolated and quantified.

Toward this end, I have employed x-ray diffraction from concentration 
modulated SiGe films as a probe of both interdiffusion and strain 
relaxation.  Although less commonly applied to semiconductor diffusion than 
techniques that map out concentration profiles directly, this technique has 
a long history as an ultra-high-sensitivity probe of both interdiffusion 
and film strain.  By growing and analyzing a series of films with varied 
mean Ge concentrations, spatial modulation periods, and degrees of strain 
relaxation, I have built up a model for concentration and strain-dependent 
Si/SiGe interdiffusion.  The model results have been successfully tested 
against x-ray measurements of interdiffusion in large-amplitude Si/SiGe 
superlattices and SIMS measurements of intermixing at Si/SiGe 
interfaces.  Further, this model is readily applicable to predicting the 
thermal stability of technologically important Si/SiGe interfaces during 
device processing.

=====
Daniel B. Aubertine
PhD Candidate
Department of Materials Science & Engineering
Stanford University
Room 203, McCullough Bldg.
476 Lomita Mall
Stanford, CA 94305-4045
URL: www.stanford.edu/~auber
Ph: 650-724-5371 (office)
Fax: 650-736-1984




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