Terahertz time-domain spectroscopic ellipsometry: Instrumentation and calibration

We present a new instrumentation and calibration procedurefor terahertz time-domain spectroscopic ellipsometry (THz-TDSE) that isa newly established characterization technique. The experimental setup iscapable of providing arbitrary angle of incidence in the range of 15◦–85◦in the reflection geometry, and with no need for realignment. The setupis also configurable easily into transmission geometry. For this setup, wesuccessfully used hollow core photonic band gap fiber with no pre-chirpingin order to deliver a femtosecond laser into a THz photoconductive antennadetector, which is the first demonstration of this kind. The proposedcalibration scheme can compensate for the non-ideality of the polarizationresponse of the THz photoconductive antenna detector as well as thatof wire grid polarizers used in the setup. In the calibration scheme, theellipsometric parameters are obtained through a regression algorithm whichwe have adapted from the conventional regression calibration methoddeveloped for rotating element optical ellipsometers, and used here for thefirst time for THz-TDSE. As a proof-of-principle demonstration, results arepresented for a high resistivity silicon substrate as well as an opaque Sisubstrate with a high phosphorus concentration. We also demonstrate thecapacity to measure a few micron thick grown thermal oxide on top of Si.Each sample was characterized by THz-TDSE in reflection geometry withdifferent angle of incidence.