AVS 56th International Symposium & Exhibition
    Plasma Science and Technology Thursday Sessions
       Session PS1-ThA

Paper PS1-ThA10
Charge Trapping and Valence-band Structure of VUV-Irradiated BEOL Dielectrics

Thursday, November 12, 2009, 5:00 pm, Room A1

Session: Fundamentals of Plasma-Surface Interactions II
Presenter: J.L. Lauer, University of Wisconsin-Madison
Authors: J.L. Lauer, University of Wisconsin-Madison
J.L. Shohet, University of Wisconsin-Madison
Y. Nishi, Stanford University
A. Antonelli, Novellus Corporatiion
Correspondent: Click to Email
The minimum spacing between conductive lines in advanced integrated circuits (ICs) continues to decrease with each generation of technology. As a result, the long-term reliability of ICs is becoming increasingly dependent on the reliability of the intermetal dielectrics which often become damaged during back-end-of-the-line (BEOL) processing. Dielectrics used in BEOL structures are often irradiated with photons of various energies during plasma processing, charge annealing, and curing of porous materials. In particular, processing plasmas produce significant amounts of vacuum ultraviolet (VUV) radiation which are, among other processes, capable of creating electron-hole pairs within dielectrics. As a result, VUV radiation has an impact on the electrical conductivity of dielectrics during plasma processing which can either contribute to or mitigate trapped charge within dielectrics. We compare the charging response of 50, 250, and 450 nm of SiOCH, SiN, SiCO, SiCN, and SiC dielectrics on Si substrates after irradiation to vacuum ultraviolet (VUV) radiation. We choose to irradiate the dielectric layers to a photon energy of 9.5 eV because photons with this energy are often emitted from processing plasmas that contain oxygen, i.e. ashing and etching plasmas. The charging response of the dielectrics was evaluated by measuring the surface potential on the dielectrics with a Kelvin probe after irradiation with several doses of 9.5 eV photons. The surface potential on all of the dielectrics after VUV irradiation was positive due to the accumulation of positive charge by traps located within the dielectrics. By comparing the surface potential on several thicknesses of dielectrics after VUV irradiation we can estimate the location within the dielectric the charge is trapped. The surface potential on SiOCH layers of varying k-values after VUV irradiation indicates the presence of both negative- and positive-charged traps. From VUV-spectroscopy, we determined the SiOCH layers have electron traps located 0.8 eV below the conduction-band edge and hole traps located 1.4 eV above the valence-band edge.

Supported by the National Science Foundation under Grant Number DMR-0306582 and the Semiconductor Research Corporation under Contract Number 2008-KJ-1781. The Synchrotron Radiation Center is funded by the National Science Foundation under Grant Number DMR-0537588.