Advances in modern semiconductor integrated circuits have always demanded faster and more sensitive analytical methods on a large-scale wafer. The surface of wafers is fundamentally essential to start building circuits, and quantitative measures of the surface potential, defects, contamination, passivation quality, and uniformity are subject to inspection. The present study provides a new approach to access those by means of terahertz (THz) emission spectroscopy. Upon femtosecond laser illumination, THz radiation, which is sensitive to the surface electric fields of the wafer, is generated. Here, we systematically research the THz emission properties of silicon surfaces under different surface conditions, such as the initial surface with a native oxide layer, a fluorine-terminated surface, and a hydrogen-terminated surface. Meanwhile, a strong doping concentration dependence of the THz emission amplitude from the silicon surface has been revealed in different surface conditions, which implies a semiquantitative connection between the THz emission and the surface band bending with the surface dipoles. Laser-induced THz emission spectroscopy is a promising method for evaluating local surface properties on a wafer scale.
Metal–insulator–semiconductor (MIS) is an essential structure in semiconductor devices. Owing to the increasingly complex development of semiconductor devices, the local information of MIS, such as passivation, defects, and transient carrier dynamics, is becoming more challenging to characterize. Laser-excited terahertz (THz) emission spectroscopy and imaging are promising for investigating such local properties in a noncontact and nondestructive manner; however, the discussions are speculative and phenomenological. In this study, we formulate the mechanism of THz radiation based on a Si metal–oxide–semiconductor (MOS) structure to semi-quantitatively evaluate the MOS devices. A simplified model for both n- and p-type Si MOS structures is derived from Poisson's equation, which can effectively explain the dependence of THz emission amplitudes on external bias voltages considering external effects, including the flatband voltage, hot carrier diffusion, and quick recombination through interface states in addition to the photocurrent due to photocarrier field acceleration. The result reveals that one can estimate various “local” parameters such as the surface potential, semiconductor doping level, and dielectric constant of the passivation layer. The simplified model fills the gap between theory and observation, resulting in an advanced analytical tool for semiconductor research and development.
This study conducted laser-induced terahertz emission spectroscopy on a VO2/Si heterojunction. Consequently, rapid estimation of the local interface potential was realized and the work function of VO2 was obtained as 5.17–5.25 eV with increasing temperature from 320 to 380 K. Moreover, an obvious terahertz emission variation was observed across the metal–insulator phase transition of VO2, and the doping conditions of the Si substrate largely influenced the terahertz emission. These results imply a strong relationship between the terahertz emission amplitude and the interface electric field, which supports the rapid performance of terahertz emission spectroscopy in estimating the work function of VO2.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.