Nondestructive extraction of junction depths of active doping profiles from photomodulated optical reflectance offset curves

The ITRS Roadmap highlights the electrical characterization of the source and drain extension regions as a key challenge for future complimentary-metal-oxide-semiconductor technology. Presently, an accurate determination of the depth of ultrashallow junctions can routinely only be performed by time-consuming and destructive techniques such as secondary ion mass spectrometry (SIMS). In this work, the authors propose to use the fast and nondestructive photomodulated optical reflectance (PMOR) technique , as implemented in the Therma-Probe® (TP) dopant metrology system, for these purposes. PMOR is a pump-probe technique based on the measurement of the pump-induced modulated change in probe reflectance, i.e., the so-called (photo) modulated reflectance. In this article, the authors demonstrate that the absolute junction depths of boxlike active dopant structures can be extracted in a very simple and straightforward way from the TP offset curves, which represent the behavior of the modulated reflectance as a function of the pump-probe beam spacing. Although the procedure is based on the insights into the physical behavior of the offset curves, no modeling is involved in the actual extraction process itself. The extracted junction depths are in good correlation with the corresponding junction depths as measured by means of SIMS. The technique has a subnanometer depth sensitivity for depths ranging from 10to35nm with the present Therma-Probe® 630XP system. The extension of the proposed procedure to the general ultrashallow profiles is also explored and discussed.