Characterization of an ultrashallow junction structure using angle resolved x-ray photoelectron spectroscopy and medium energy ion scattering

Abstract

The control of dose and energy (and therefore depth distribution) of ion implantation in n-channel MOSFET (NMOS) ultrashallow junctions is vital. Therefore there is a need to provide reliable metrology. Since the standard sheet resistance probing method, and the dynamic secondary ion mass spectroscopy method used to calibrate it both become more problematic for very shallow junctions, other techniques need to be evaluated. Angle resolved x-ray photoelectron spectroscopy (AR-XPS) is investigated here as an additional, nondestructive, laboratory-based tool to characterize NMOS junctions. The arsenic depth distribution and chemical bonding configuration are investigated for a set of p-type wafers implanted at 2keV with nominal doses from 1×1015to2×1015at.∕cm2. The results are compared to those using medium energy ion scattering (MEIS). It is demonstrated that XPS is a useful nondestructive tool for obtaining dopant chemical bonding state, qualitative elemental and chemical state depth information without modeling, and quantitative information on overlayer film thickness. Modeling the AR-XPS data and comparison to trial depth structures can lead to a more quantitative, but crude, depth profile. The combination of AR-XPS and MEIS was also able to explain why secondary ion mass spectroscopy profiling measures an approximately 2% increase for 1×1015at.∕cm2 in apparent dose on annealing the arsenic as-implanted wafer.