Reduction and creation of paramagnetic centers on surfaces of three different polytypes of SiC

Abstract

SiC is of interest to create power metal–oxide–semiconductor field-effect transistors because it can be thermally oxidized to form a ${\mathrm{SiO}}_{\mathrm{2}}$ dielectric layer. Previously, we used electron paramagnetic resonance to identify centers in 3C–SiC epilayer samples and 4H–SiC and 6H–SiC wafer samples after oxidation and dry heat treatment [P. J. Macfarlane and M. E. Zvanut, Appl. Phys. Lett. 71, 2148 (1997); Mater. Res. Soc. Symp. Proc. 513, 433 (1998)]. The spectroscopic and thermal characteristics of these centers indicate that they are related to C. Because these centers are activated in a ${\mathrm{H}}_{\mathrm{2}}\mathrm{O-poor}$ ambient and are passivated in an ambient that is ${\mathrm{H}}_{\mathrm{2}}\mathrm{O-rich,}$ we suggest that the activation mechanism is release of a hydrogenous species. In this investigation, the effect of repeated oxidations on the concentration of heat-treatment-induced centers is studied. Samples are successively oxidized at 1150 °C in ${\mathrm{O}}_{\mathrm{2}}$ bubbled through de-ionized water for 1, 2, 4, 8, and 16 h. After each oxidation, the samples are heat treated in dry (<0.1 ppm ${\mathrm{H}}_{\mathrm{2}}\mathrm{O)}$ ${\mathrm{N}}_{\mathrm{2}}\mathrm{.}$ Prior to the next oxidation, the oxide is removed. Upon oxidation of the samples we observe an order of magnitude reduction in the concentration of centers that are present on the as-prepared substrates. After each oxidation centers are activated by dry heat treatment. We suggest that the centers present on the as-prepared substrates are related to surface damage and are removed during the oxidation as the surface SiC material is converted in the oxidation products. Two models are offered for the source of the centers generated by dry heat treatment. The centers could be activated from C–H bonds related to damage like micropipes, nanopipes, or Si vacancies distributed throughout the SiC substrate, or they could arise from C–H bonds that form during the oxidation. We will discuss the merits of both of these models.