Oxidation-enhanced annealing of implantation-induced Z 1 / 2 centers in 4H-SiC: Reaction kinetics and modeling
2012; American Physical Society; Volume: 86; Issue: 7 Linguagem: Inglês
10.1103/physrevb.86.075205
ISSN1550-235X
Autores Tópico(s)Thin-Film Transistor Technologies
ResumoHigh-purity epitaxial layers of $n$-type 4H-SiC have been implanted with 4.3-MeV Si ions to a dose of 3 $\ifmmode\times\else\texttimes\fi{}$ 10${}^{8}$ cm${}^{\ensuremath{-}2}$ and then subjected to dry isothermal oxidation at temperatures between 1050 and 1175 \ifmmode^\circ\else\textdegree\fi{}C. Analysis of the samples by depth-resolved deep level transient spectroscopy unveils a strong oxidation-enhanced annealing of the prominent Z${}_{1/2}$ center, commonly ascribed to the carbon vacancy. The integrated (total) loss of Z${}_{1/2}$ centers is proportional to the thickness of the silicon dioxide (SiO${}_{2}$) layer grown but the proportionality constant, or annihilation efficiency, decreases with decreasing oxidation temperature. At a given depth $x$, the annealing of Z${}_{1/2}$ obeys first-order kinetics with a rate constant $c$ having an activation energy of \ensuremath{\sim}5.3 eV. The pre-exponential factor $c$ decreases with increasing $x$ and a normalized concentration-versus-depth distribution of the species injected from the surface and annihilating the Z${}_{1/2}$ centers has been deducted. This species is believed to be the carbon interstitial and is labeled C${}_{\mathrm{I}}$: numerical simulations of the reaction kinetics employing a model where (i) the generation rate of C${}_{\mathrm{I}}$ at the SiO${}_{2}$/SiC interface is related to the oxidation rate, (ii) the diffusion of C${}_{\mathrm{I}}$ into the SiC layer is fast, and (iii) a steady-state concentration profile of C${}_{\mathrm{I}}$ is rapidly established, yield good agreement with the experimental data for the evolution of both Z${}_{1/2}$ (absolute values) and C${}_{\mathrm{I}}$ (relative values) with temperature, depth, and time. The activation energy obtained for the diffusivity of C${}_{\mathrm{I}}$ is \ensuremath{\sim}3.0 eV, presumably reflecting the migration barrier for C${}_{\mathrm{I}}$ and possibly some contribution from an extra barrier to be surmounted at the SiO${}_{2}$/SiC interface.
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