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The silicon dioxide/silicon interface is critical in the electrical behavior of metal-oxidesemiconductor
(MOS) field-effect transistors. As device dimensions shrink, roughness at this
interface becomes increasingly important to electrical properties for two reasons. Roughness-induced
local thickness variations lead to more significant fluctuating electric fields, and oxide growth
temperatures must be reduced for thin oxides, leading to greater roughness. In this paper several
experiments are described which provide information on the degree of roughness and its origin
during the oxidation process. There are two types of experiments discussed: direct observation of
atomic steps and structure during the very initial stages of room-temperature oxide growth on ultraclean
Si(1 1 1) surfaces, and determination of roughness at conventional furnace-grown Si/SiO2
interfaces by a novel electron diffraction technique. The results of both these studies suggest that
oxidation occurs primarily by the breaking of backbonds adjacent to the interface, and not by a
terrace-ledge-kink mechanism. As a result, roughness is intrinsically created by the oxidation
process, and can be removed only by a post-oxidation anneal. There is also evidence that the
interface tension of Si/Si02 is sufficiently high, especially on Si(1 1 1), that it drives interface
flattening during non-oxidizing thermal anneals.
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