ELSEVIER Microelectronic Engineering 40 (1998) 131-146 laC~mflmtBn Application of Charge Pumping Technique for sub-micron MOSFET Characterization C.R.Viswanathan and V. Ramgopal Rao Electrical Engineering Department, University of California, Los Angeles, CA 90095-1594, USA In this paper, charge pumping technique for MOSFET interface characterization will be reviewed. The basic principles of charge pumping technique will be elaborated and its evolution as an excellent tool for a thorough characterization of MOSFET interface properties will be illustrated. Published results regarding the applicability of charge pumping technique for a study of sub-micron MOSFET interface and its degradation under various electrical stress conditions and radiation will be analyzed. The effect of geometric components on charge pumping current as well as the recent reports of single interface trap characterization in sub-micron MOSFETs will be described. The application of charge pumping technique at cryogenic temperatures and in other MOS based devices will also be included. 1. INTRODUCTION During the last decade, charge pumping (CP) technique, originally discovered by Burgler and Jespers in 1969, has evolved as the most powerful technique for interface characterization in MOS transistors [1]-[21. Even for the present day ultra small MOSFETs, the charge pumping technique proved to be extremely useful, since no other technique allows the probing of MOS interface properties with the same kind of simplicity and accuracy. This can be gauged from the recent demonstrations [3]-[5] where charge pumping has been used to resolve individual interface traps in sub-micron MOSFETs and from the reports that single interface trap generation [3] in deep sub- micron MOSFETs under hot-carrier stress can be monitored with charge pumping. The major advantage of the charge pumping (CP) technique however is that the measurements are done on the actual transistor itself without needing a separate test device. The need to extrapolate the results obtained on a test capacitor to characterize the interface in a transistor is thus eliminated. The technique yields precise results. Several authors have developed different ways of applying the charge pumping principle for the determination of the average density of interface traps [6]-[9], their energy and spatial distributions [9]-[15], the geometric mean value of the capture cross section for electrons and holes [9], and recently even the reverse short channel effect in sub-micron MOSFETs [16]. This technique is adequate for the evaluation MOSFET degradation due to electrical stress and radiation damage [17]- [251. Much work has been carried out over the last 2 decades in order to improve the understanding of the technique [1]-[2]. The basic principle of the technique is discussed in Section 2. The presence of geometric components in the charge pumping current was first reported by Brugler and Jespers [6]. The geometric component originates from free minority carriers that do not have enough time to escape via source and drain during the switch-off of the gate pulse. It is very important either to eliminate the geometric component, or to separate it from the actual interface trap component of the charge pumping current. Section 3 deals with this issue of separating the geometric component from the actual charge pumping current. The modifications to the basic charge pumping technique to extract energy distribution of interface traps, as well as the lateral and vertical spatial profiles of the interface traps and/or of the trapped oxide charge is discussed in Section 4. A demonstration of the extremely high sensitivity of the technique was reported recently [3]-[5] by the observation of single interface traps in sub-micron MOSFET's, which is the subject of Section 5, in 0167-9317/98/$- see front matter Copyright© 1998 Elsevier Science B.V. All rights reserved. PII: S0167-9317(98)00266-4