AVS 46th International Symposium
    Nanometer-scale Science and Technology Division Friday Sessions
       Session MS+PS-FrM

Paper MS+PS-FrM5
Measurement of Residual Fluorine in a Polysilicon Etch Reactor with Fourier Transform Infrared Spectroscopy (FTIR)

Friday, October 29, 1999, 9:40 am, Room 611

Session: Diagnostics and Processes in Etching
Presenter: J.E. Daugherty, Lam Research Corporation
Authors: J.E. Daugherty, Lam Research Corporation
E. Edelberg, Lam Research Corporation
V. Vahedi, Lam Research Corporation
A. Perry, Lam Research Corporation
J. Huang, Lam Research Corporation
R. Marsh, Lam Research Corporation
Correspondent: Click to Email
One challenge in sub-0.18 µm gate etching is maintaining the integrity of the thin (<25 Å) gate oxide. This task is especially difficult for in situ hardmask applications where a dielectric (SiO@sub 2@ or Si@sub 3@N@sub 4@) hardmask is etched with a fluorine-containing gas (e.g., CF@sub 4@) in the same chamber that the underlying polysilicon gate is etched with Cl@sub 2@ and HBr. Fluorinated molecules can be released from in-chamber etch residues for several minutes after the fluorine-containing etchant is turned off, and free fluorine is produced when the plasma subsequently dissociates these compounds. If there is sufficient fluorine remaining in the chamber after the polysilicon is etched, it can reduce the selectivity to the underlying gate oxide. A similar reduction of the gate oxide selectivity is often noticed immediately following a dry clean of the etching chamber (i.e., a plasma clean). Since the chamber is cleaned with SF@sub 6@ or NF@sub 3@ plasma, residual fluorine from the cleaning plasma sometimes reduces the amount of remaining gate oxide on the first wafer processed after the clean. We have used Fourier transform infrared spectroscopy (FTIR) to measure the concentration of several fluorine-containing etch products (e.g., SiF@sub 4@, HF) during gate etching with Cl@sub 2@/HBr in an inductively coupled plasma reactor. We have verified that the etch rate of thermal SiO@sub 2@ in Cl@sub 2@/HBr mixtures increases with increasing concentration of residual fluorinated etch products in the effluent of the reactor. We also observe that for in situ hardmask etching, the amount of fluorine-containing etch product that is observed at the end of the polysilicon etch step depends on the duration of fluorine exposure during the hardmask etch step.