Abstract

We describe techniques for characterization of doping concentration profile of semiconductors via terahertz deep-level spectroscopy, direct volume-imaging, and an empirical modeling approach. Since the semiconductors are doped mainly via diffusion and ion implantation techniques, the doping concentration is not always uniform across the thickness. Hence, it is important to determine the doping concentration profile across the depth. The deep-level spectroscopy allows (i) to construct a profile of doping concentration across the depth of a wafer or other substrates and (ii) spectral analysis of subsurface layers via absorbance peaks. The direct volume-imaging is used for quantitative dimensional metrology of layers with different compositions such as epitaxial layer thickness and lattice parameter of constituent layers. High resolution images may also be used for lattice scale interface analysis. Finally, an empirical approach has been described for modeling the doping concentration. This empirical route may be used for modeling any dopant-substrate combination. Such model for a given substrate is useful for instantaneous evaluation of doping concentration by the measured reflected intensity of incident T-ray beam. Specific practical examples have been used to described each of the three techniques; all provided via a single experimental setup.

Keywords: Doping concentration, Depth profile, Deep-level spectroscopy, reflectance modeling, volume imaging