AVS 47th International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS1+MS-WeA

Paper PS1+MS-WeA7
Productivity Solutions for Eliminating Within-Wafer and Wafer-to-Wafer Variability in a Silicon Etch Process through Plasma and Surface Diagnostics

Wednesday, October 4, 2000, 4:00 pm, Room 310

Session: Sensors and Control in Plasma Processing
Presenter: E.A. Edelberg, Lam Research Corporation
Authors: E.A. Edelberg, Lam Research Corporation
L.B. Braly, Lam Research Corporation
V. Vahedi, Lam Research Corporation
J. Daugherty, Lam Research Corporation
S.J. Ullal, University of California, Santa Barbara
A.R. Godfrey, University of California, Santa Barbara
E.S. Aydil, University of California, Santa Barbara
H.K. Chiu, Taiwan Semiconductor Manufacturing Corp.
H.J. Tao, Taiwan Semiconductor Manufacturing Corp.
Correspondent: Click to Email
Various plasma and surface diagnostics were used to understand the root causes that lead to within-wafer and wafer-to-wafer variability in critical dimension (CD) loss in Si etch applications. It is found that the conditions of the reactor walls can play a significant role in determining the plasma properties and therefore the figures of merit of the etching process. Etch products from the wafer can adsorb and build up on the walls of the chamber leading to changes in the wall properties. These changes can lead to drifts in the plasma properties and cause wafer-to-wafer variability of the etch process. It is demonstrated that such drifts can be avoided by cleaning the walls of the reactor using Fluorine-containing plasmas in between wafers. We demonstrate that a fundamental understanding of the chemistry and composition of the deposited materials on the walls of the chamber and their relation to the gas phase species can be used to develop and optimize appropriate reactor wall cleaning processes. A multiple pass downstream Fourier transform infrared (FTIR) spectrometer is used to quantitatively measure the concentration of gas phase species such as SiCl@sub 4@ and SiF@sub 4@ in the reactor exhaust. In addition, a novel diagnostic technique based on the principles of multiple total internal reflection FTIR spectroscopy is used to measure, in situ, the presence and composition of material deposited or removed from the walls of the chamber. In particular, during Si etching processes with Cl@sub 2@/O@sub 2@ plasmas, the deposited films were found to be the byproducts of the etching reactions and contain Si, O and Cl. We show that performing a short plasma chamber clean with the appropriate chemistry between each wafer can reduce the wafer-to-wafer variability of both etch rate and CD bias. By performing an in situ clean after every wafer during a 0.13 micron gate etching process the wafer-to-wafer repeatability is reduced to 2nm (at 3 sigma).