AVS 52nd International Symposium
    Plasma Science and Technology Friday Sessions
       Session PS-FrM

Paper PS-FrM7
Depletion of Plasma-Induced Charge on Semiconductor Dielectrics using Ultraviolet and Vacuum Ultraviolet Radiation

Friday, November 4, 2005, 10:20 am, Room 302

Session: Plasma Surface Interactions III
Presenter: G.S. Upadhyaya, University of Wisconsin-Madison
Authors: G.S. Upadhyaya, University of Wisconsin-Madison
J.L. Shohet, University of Wisconsin-Madison
J.L. Lauer, University of Wisconsin-Madison
R.W.C. Hansen, University of Wisconsin-Madison
Correspondent: Click to Email
Radiation-induced charging during the processing of semiconductor materials can adversely affect device reliability. We have reported previously that vacuum ultraviolet (VUV) radiation with energies between 7-30eV can cause ionizing collisions in the dielectric creating charge carriers, thereby increasing the dielectric conductivity. However, the most dominant form of plasma-induced damage on a semiconductor dielectric is from electron and ion bombardment. As technology progresses, is more problematic because of increasing feature aspect ratios, Ions tend to collect at the bottom of high-aspect-ratio trenches while the lighter electrons crowd the trench walls, thus "shading" the ions. This electron-shading effect is not well documented due to the lack of a reliable diagnostic. In-situ techniques for depleting plasma-deposited charge will be an invaluable tool for manufacturing high quality devices. To this end, a technique for depleting plasma-induced charge by exposing plasma-charged wafers to either ultraviolet (UV) or VUV has been developed. Photons with energies ranging from 5-12eV possess sufficiently large penetration depths so as to photo-inject carriers from the substrate and thus deplete the previously deposited charge by conductive effects. Silicon wafers with silicon oxide or silicon nitride of thicknesses between 200 and 3000 Å grown on silicon were precharged to range of surface potentials of the order 4-10 volts by exposure to a 13.56 MHz RF plasma. The wafers were then exposed to synchrotron radiation with photon energies between 5-12 eV. From the comparison of the surface potential distributions before and after UV/VUV exposure, it is possible to determine the penetration depth of the VUV, the conditions for photoemission and photoconductivity, as well as the effectiveness of charge depletion as a function of photon energy and dielectric thickness. @FootnoteText@ Work supported by NSF under grants DMR-0306582. and DMR-0084402.