Detection and Characterization of Single Defects in MOSFETs

Abstract

Charge pumping (CP) technique is known to be a highly precise method for evaluating the density of interface defects between the gate oxide and the semiconductor surface in MOSFETs. Recently, a unique and systematic characterization of genuine single MOS interface defects was carried out using the CP method. Based on the experimental results, it is shown in this chapter that two energy levels participate in electron capture/emission processes in a single defect, and it is clarified that the CP current per defect shows various values in the range of 0–2fq, but not a fixed value of fq, which is the conventional belief (f: the gate pulse frequency, q: the electron charge). This results from the differences in the pairs of donor-like and acceptor-like defect energy levels. These results mean, in other words, the first success of direct and electrical observation of single P _b0 centers. The distribution of the energy levels of these single defects is also obtained for the first time. The distribution is reasonably similar to that of the P _b0 density of states reported previously. By considering the essential nature of these defects, the conventional CP theory is fundamentally corrected. Moreover, a novel method is proposed for characterizing the individual oxide defects that participate in random telegraph noise (RTN) using charging history effects on the defects. In this method, the variation in the frequency of the high/low drain current derived from RTN with the charging history is monitored instead of the timescale parameters that are usually used. To help the novel method, a simple procedure to determine the number and charging conditions of the defects is also proposed. These methods are particularly effective for characterizing individual oxide defects in multi-defect RTN.