Development and applications of a new deep-level transient spectroscopy method and new averaging techniques.

摘要

In this thesis, we report new advancements in the field of Deep Level Transient Spectroscopy (DLTS) which is a powerful method for investigation of electrically active point defects in semiconductors. We demonstrate these advancements by building a state-of-the-art DLTS system and performing extensive measurements on several types of field-effect transistors (FETs).;We introduce a new approach to digital signal processing in DLTS systems. The problems of signal recovery from noise and efficient data storage are addressed separately from the transient signal analysis. We combine two complementary digital averaging techniques which substantially improve the DLTS digital signal processing. Compared to other digital DLTS systems, the new averaging techniques offer an improved time resolution at the beginning of the transient, improved signal-to-noise ratio, and more efficient data storage. At the same time it offers real-time observation of essentially noise-free transients and real-time data processing.;We designed and fabricated a new feedback circuit which solves the speed and sensitivity problems of constant-capacitance (CC-) DLTS. The speed of the feedback circuit is demonstrated by comparing recorded traces from CC-DLTS with conventional capacitance-transient DLTS. Sensitivity is demonstrated with measurements of the interface trap density of virgin and hot-carrier stressed metal-oxide-semiconductor (MOS)FETs. After a slight modification, the same feedback circuit makes technically possible a new method which we call constant-resistance (CR-)DLTS.;The new CR-DLTS method is similar to the conductance DLTS, but it is more sensitive and it does not require other measurements for calculation of the trap concentrations. Unlike the conductance or current DLTS, in the new CR-DLTS technique the test transistor operates at very low current levels and stressing of the device is avoided. In addition, the CR-DLTS signal is largely independent of the transistor size, thus allowing measurements of very small-size transistors. Since the sensitivity of CR-DLTS is proportional to the gain of the transistor (or the aspect ratio), it is completely independent of the area of the test device which is not true for CC-DLTS. We demonstrate this new method by measurements of virgin submicron MOSFETs, but the technique can be used also to study other field-effect transistors.;Next, CR-DLTS is demonstrated with measurements of proton radiation-induced traps in buried channel MOSFETs which are used as CCD output amplifiers. The unique structure of these devices offers extended opportunities for studying the space distribution of the radiation induced defects. In addition, we show. a variation of the CR-DLTS technique using back-gate driving, which is applicable for studying the channel-substrate p-n junction, and the results are compared with those obtained from CC-DLTS measurements.;Finally, CR-DLTS was also successfully applied to study virgin and radiation-damaged Si and Ge junction field-effect transistors (JFETs). CR-DLTS was confirmed to be a simple, very sensitive, and area independent technique which is well suited for measurement of a wide range of deep level concentrations. Comparisons have been made again with the CC-DLTS and conventional DLTS. In addition, new possibilities for defect profiling in the channel have been demonstrated.;We expect, that the results from this thesis will be useful for many new applications of DLTS, previously not available. Also, the described averaging and data reduction techniques can be useful for many other applications involving transient data recording and analysis.