Reduction and creation of paramagnetic centers on surfaces Of three different polytypes of SIC

SiC is of interest to create power metal-oxide-semiconductor field-effect t ransistors because it can be thermally oxidized to form a SiO2 dielectric l ayer. Previously, we used electron paramagnetic resonance to identify cente rs in 3C-SiC epilayer samples and 4H-SiC and 6H-SiC wafer samples after oxi dation and dry heat treatment [P. J. Macfarlane and M. E. Zvanut, Appl. Phy s. Lett. 71, 2148 (1997); Mater. Res. Sec, Symp. Proc. 513, 433 (1998)]. Th e spectroscopic and thermal characteristics of these centers indicate that they are related to C. Because these centers are activated in a H2O-poor am bient and are passivated in an ambient that is H2O-rich, we suggest that th e activation mechanism is release of a hydrogenous species. In this investi gation, the effect of repeated oxidations on the concentration of heat-trea tment-induced centers is studied. Samples are successively oxidized at 1150 degrees C in O-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 H2O) N-2. Prior to the next oxidation, the oxide is removed. Upon oxidation of t he samples we observe an order of magnitude reduction in the concentration of centers that are present on the as-prepared substrates. After each oxida tion centers are activated by dry heat treatment. We suggest that the cente rs present on the as-prepared substrates are related to surface damage and are removed during the oxidation as the surface SiC material is converted i n the oxidation products. Two models are offered for the source of the cent ers generated by dry heat treatment. The centers could be activated from C- H bonds related to damage like micropipes, nanopipes, or Si vacancies distr ibuted throughout the SIC substrate, or they could arise from C-H bonds tha t form during the oxidation. We will discuss the merits of both of these mo dels. (C) 1999 American Vacuum Society. [S0734-211X(99)09004-6].