Non-contact measurement of dopant depth profile with terahertz emission spectroscopy

Abstract

Depth profile of the dopant concentration in silicon substrate has a crucial influence on the electric characteristics that defines the device performance, whereas those profile has only been evaluated by destructive methods, most typically Secondary-Ion Mass Spectrometry (SIMS). We applied Terahertz Emission Spectroscopy (TES) that exploits charge carrier drift within the built-in potential structure to p-n junction structure in order to non-destructively extract the information about carrier dynamics and consequently the dopant profile. We prepared samples composed of Boron doped region as a p-Si and Phosphor doped region as a n-Si with a different p-n junction depth, and the TES evaluation was conducted illuminating the pump beam with the wavelength of 400nm. The obtained signals exhibit a clear difference among each sample in spite of the junction depth difference of as small as 15nm. The depth sensitivity of TES measurement was also investigated by utilizing carrier dynamics simulation, and clearly indicates the sensitivity to dopant depth profile, which is consistent with experimental TES signal. These results suggest that TES technology is very promising as in-line dopant profile measurement tool which is currently unrealistic with existing technologies and expected to greatly enhance the process control capability.