AVS 47th International Symposium
    Thin Films Wednesday Sessions
       Session TF+EL-WeA

Paper TF+EL-WeA9
In-Situ Monitoring of Adsorption and Film Growth Using Infrared Reflection Absorption Spectroscopy

Wednesday, October 4, 2000, 4:40 pm, Room 203

Session: In-situ Characterization of Thin Film Growth
Presenter: V.M. Bermudez, Naval Research Laboratory
Authors: V.M. Bermudez, Naval Research Laboratory
W.J. DeSisto, Naval Research Laboratory
Correspondent: Click to Email
Chemical methods for thin-film growth and processing, such as CVD, suffer from a lack of techniques for surface-sensitive, chemically-specific diagnostics under steady-state conditions. Infrared reflection absorption spectroscopy (IRRAS) has been demonstrated as a viable approach to addressing this need. Polarization modulation (PM) has been coupled with a Fourier transform IR spectrometer, permitting the use of linear dichroism to distinguish weak, polarized surface absorptions from strong, isotropic gas-phase absorptions. Buried metal layers have been used both to increase the IRRAS sensitivity to adsorbates on nonmetallic surfaces and to impose the high degree of polarization needed for detection of surface species. Numerical modelling, via the Fresnel relations, has also been included as an integral part of the experiment. This approach has been used to observe the different @delta@@sub s@ frequencies of NH@sub 3@ adsorbed on Al nitride, oxide and oxynitride in a 200 Torr NH@sub 3@ ambient, which can be understood in terms of the different Lewis acidities of the surface Al cations. The optical system has been mated with a production CVD facility and used to observe the steady-state growth of Cr@sub 2@O@sub 3@ thin films on Al@sub 2@O@sub 3@ by reaction of Cr(CO)@sub 6@ and O@sub 2@ at @<=@270 °C. The T-dependence of the physisorbed Cr(CO)@sub 6@ coverage measured with PM-IRRAS gives a desorption energy of 11 Kcal/mol, indicating a weak interaction with the substrate. The growth rate of the Cr@sub 2@O@sub 3@ film is first-order in the Cr(CO)@sub 6@ pressure (both quantities having been obtained from IR data). Modeling of the IR data shows interfacial roughness to be important in this system.