CHEMICAL VAPOR DEPOSITION OF THIN FILM MATERIALS FOR ...

statistical roughening. For epitaxy, one more parameter, lattice mismatch is also important for
determining the film growth mode.[15] The lattice mismatch (f) is defined as below,
f a f -a s a s
where af and as represent the atomic spacings along some direction in the film and substrate
crystal, respectively. When the thermal expansion coefficients of the two materials are different,
f becomes a function of T and this will also contribute to the temperature dependence of thin film
growth mode or surface topography development.[16,17] For example, at certain high growth
temperatures, due to the difference of thermal expansion, the lattice mismatch becomes large
enough to induce much larger interfacial energy (γi) and thus inequality Eqa. (1.5) will fail and
the thin film growth will change to 3D island mode.
1.2.3 Thin Film Characterization
17
(1.6)
Thin film characterization includes in situ monitoring of thin film growth behavior and
post deposition measurement of various film properties. The in situ monitoring of thin film
growth can provide continuous updated information such as chemical composition, crystal
structure, surface topography, film thickness, and optical properties, etc.. For instance, reflection
high energy electron diffraction (RHEED) can be used to detect surface crystallographic
information in epitaxy. The RHEED pattern is an instantaneous reflection of the arrangement of
atoms on a thin film surface.[18] Other in situ monitoring tools, such as attenuated total
reflectance Fourier transform infrared spectroscopy (ATR-FTIR), ellipsometry, quartz crystal
microbalance (QCM) are also widely used. Post deposition measurement has a much wider
window of option of analysis techniques. For example, for the chemical composition analysis, X-
ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Energy dispersive X-