AVS 51st International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS-MoP

Paper PS-MoP4
A New Plasma Source for Destruction of Organic Material in the Post Chamber Hardware, and Implications for Process Endpoint Detection for Specific Low-k Applications.

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: A.K. Srivastava, Axcelis Technologies, Inc.
Authors: A.K. Srivastava, Axcelis Technologies, Inc.
P. Sakthivel, Axcelis Technologies, Inc.
T.J. Buckley, Formerly, Axcelis Technologies, Inc.
A.F. Becknell, Axcelis Technologies, Inc.
Correspondent: Click to Email
The high temperature ash of photoresist in the presence of certain oxygen-sensitive low k materials requires a plasma discharge devoid of conventional oxidizing agents. In such cases, the chemistries active on the wafer do not entirely destroy the long chain organic polymers that make up the resist. Instead, some of the photoresist is re-deposited on the chamber walls, as well as in the hardware downstream of the wafer. Specifically, parts of the vacuum system comprising the throttle valve, foreline valve and pump lines get coated with organic material, which then have to be manually cleaned during frequent maintenance periods. This leads to significant down time for the ash tool. Due to this oxidizer-free process, there are few emissions in the visible region of the spectrum from reactions at the wafer surface, which makes conventional optical emission based end-point schemes mostly unusable. A compact plasma system has been developed that creates an intense radio frequency (RF) discharge in the exhaust line below the process chamber. Using a secondary inlet for oxidizer agents, the plasma system combusts all incoming organic material before it has a chance to redeposit on the post chamber hardware. Data will be shown on the observed destruction efficiency. Additionally, analysis of the plasma using a residual gas analyzer (RGA), as well as an optical spectrograph to obtain crucial information on the reaction chemistries will be presented. RGA data from diffusion tests show that no oxidizing agent from the downstream inlet makes its way upstream into the chamber where it could potentially harm the low-k material on the wafer. Finally, successful oxidation of the organic material in the plasma source gives rise to optical signals downstream of the chamber that can be used very effectively to extract endpoint for resist removal from the wafer surface.