In situ on-wafer monitoring of the electron and ion energies at the contact-hole bottom is primarily achieved in Ar ultrahigh-frequency plasma. The on-wafer probe reveals a lower electron density and higher electron temperature at the contact-hole bottom due to the electron-shading effect, as compared with that in the bulk plasma. The on-wafer probe also shows the ion energy distribution function (IEDF) at the contact-hole bottom. The peak energy of IEDF corresponded to the sheath potential. Accordingly, the authors found that the on-wafer probe is a very effective tool for investigating the electron and ion energies in real SiO2 contact structures. (c) 2007 American Vacuum Society.