AVS 45th International Symposium
    Applied Surface Science Division Friday Sessions
       Session AS+VT-FrM

Paper AS+VT-FrM8
Measurement of Carrier Concentration and Lattice Absorption in Bulk and Epitaxial Silicon Carbide Using Infrared Ellipsometry

Friday, November 6, 1998, 10:40 am, Room 307

Session: Application of Surface Analysis Techniques to Semiconductor Technology
Presenter: T.E. Tiwald, University of Nebraska, Lincoln
Authors: T.E. Tiwald, University of Nebraska, Lincoln
S. Zollner, Motorola Semiconductor Products Sector
J.A. Woollam, University of Nebraska, Lincoln
J. Christiansen, Motorola Semiconductor Products Sector
P.G. Snyder, University of Nebraska, Lincoln
Correspondent: Click to Email
We have measured the dielectric function of bulk nitrogen-doped 4H and 6H SiC substrates from 700 to 4000 cm@super -1@ using Fourier-transform infrared spectroscopic ellipsometry. We observe a strong reststrahlen band between 800 and 1000 cm@super -1@ due to photon absorption by transverse optical phonons. The shape of this band is influenced by plasma oscillations of free electrons, which can be described with the Drude model. A detailed analysis of the data allows the determination of the free electron concentration, which is between 10@super 18@ and 10@super 19@ cm@super -3@, in good agreement with electrical measurements. We were also able to determine the surface layer thickness for epitaxial 4H SiC (with an electron concentration of 10@super 16@ cm@super -3@) on heavily-doped bulk 4H SiC. Finally, we observe Berreman peaks near the longitudinal optical phonon energy in all samples. These interference effects are the result of carrier depletion and accumulation near the surface. The effect is strongest in the epitaxial sample and the more lightly doped substrates.