AVS 52nd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThM

Paper PS-ThM3
Innovative Strategy to Improve the Stability of Plasma Processes

Thursday, November 3, 2005, 9:00 am, Room 304

Session: Plasma-Surface Interactions II
Presenter: R. Ramos, CNRS/LTM, France
Authors: R. Ramos, CNRS/LTM, France
G. Cunge, CNRS/LTM, France
B. Pelissier, CNRS/LTM, France
O. Joubert, CNRS/LTM, France
Correspondent: Click to Email
Plasma process drifts associated with changes in the reactor wall conditions have become a major issue in silicon etching processes used in integrated circuit fabrication. The solution today to achieve good wafer-to-wafer repeatability is the dry-cleaning of the chamber in fluorine-based plasma between each wafer. However, this procedure leaves AlF residues on the Al@sub 2@O@sub 3@ reactor walls. This leads to several issues including flake off of AlF@sub x@ particles on the wafer and process drifts - due both to the progressive growth of AlF material and to the release of F atoms from the chamber walls during the etching process. For all these reasons, we are introducing here a new strategy to improve the stability of plasma processes. Before the etching process, a thin carbon-rich layer is deposited on the reactor walls by a short plasma step. After silicon gate etching, the SiOCl layer formed on the carbon layer is cleared with an appropriate plasma chemistry and the carbon layer removed by an O@sub 2@ plasma, thus resetting the reactor walls to their initial state. Using this strategy the process is perfectly reproducible since it always starts under the same carbon-rich chamber walls conditions. At the same time, issues associated with AlF deposits are prevented because chamber walls are protected from aggressive fluorine-based cleaning plasma. X-ray Photoelectron Spectroscopy analysis of the reactor wall surfaces is used to show feasibility and efficiency of this technique in an industrial context. Then performance of state-of-the-art silicon gate etching process in carbon-coated chamber and in traditionally seasoned chamber are compared in terms of feature profile, etch rate and selectivity toward gate oxide. Correlation with time-resolved broad-band UV absorption spectroscopy analysis of plasma gaseous phase suggests promising future of this strategy for metal gate etching.