The occurrence of the hysteresis-like breakdown (denoted by BD-H) and the minority carrier generation in MOS structures under substrate injection enhanced by the direct illumination treatment in a rapid thermal processing (RTP) are examined in this study. It is generally believed that the oxide breakdown under substrate injection is related to the oxide quality and the minority carrier generation contributed by bulk traps in Si substrate. For the breakdown behavior of MOS devices subjected by substrate injection, we find that the occurrence frequency of BD-H is more for the samples treated by the front-side heating (FH) processing than for those done by the back-side heating (BH) one in RTP. Besides, it is also observed that the gate saturation current is under the influence of the direct illumination processing. Moreover, from capacitance-voltage (C-V) measurements with various frequencies, it indicates that the generation rate of minority carriers is higher for the samples treated by FH processing than for those done by BH one. These results show that not only localized oxide traps but also Si bulk traps are much easy to be created in the direct illumination processing. It is, therefore, clear that the characteristics of MOS structures with ultra-thin oxides are influenced by the direct illumination in RTP. (c) 2005 Elsevier Ltd. All rights reserved.