AVS 47th International Symposium
    Thin Films Wednesday Sessions
       Session TF+EL-WeA

Paper TF+EL-WeA2
Ultraviolet Absorption Spectroscopy of Polytetrafluoroethylene Deposition by Pyrolytic CVD

Wednesday, October 4, 2000, 2:20 pm, Room 203

Session: In-situ Characterization of Thin Film Growth
Presenter: B.A. Cruden, Massachusetts Institute of Technology
Authors: B.A. Cruden, Massachusetts Institute of Technology
K.K. Gleason, Massachusetts Institute of Technology
H.H. Sawin, Massachusetts Institute of Technology
Correspondent: Click to Email
Polytetrafluoroethylene films have been deposited for use low dielectric constant materials in microelectronic chips. Deposition is performed through pyrolysis of hexafluoropropylene oxide (HFPO) to produce CF@sub 2@, which can then polymerize and deposit as a thin film. The variation of CF@sub 2@ concentration as a function of reactor conditions has been characterized by UV Absorption spectroscopy. CF@sub 2@ concentration is observed to go through a maximum with respect to both pressure and pyrolysis temperature when it is present in large amounts (~10@sup 14@ cm@sup -3@). The kinetics known for HFPO cracking and CF@sub 2@ recombination are not sufficient to describe these dependencies. An additional mechanism of particle formation, by CF@sub 2@ insertion into (CF@sub 2@)@sub n@ oligomers, has been introduced to produce a kinetic model for CF@sub 2@ concentration measurements. Deposition rates are seen to qualitatively track with CF@sub 2@ concentration variations. Attempting to develop a specific relationship between CF@sub 2@ concentration and deposition rate yields a sticking coefficient of ~4x10@sup -5@, which is consistent with what has been measured in a CF@sub 2@ beam experiment. However, this result does not adequately describe deposition profiles, and under some conditions, higher deposition rates than this sticking coefficient allows for have been observed. These results point to two important factors. First, under regimes of high CF@sub 2@ concentration, gas phase polymerization can produce species that contribute significantly to deposition. Second, it is possible that other properties of the deposition can affect the sticking coefficient. The final observation of note is that deposition only becomes detectable when CF@sub 2@ concentration approaches its maximum value. This might imply that (CF@sub 2@)@sub n@ species may be responsible for deposition.