Vapor deposition of parylene-F using hydrogen as carrier gas
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Vapor deposition of parylene-F using hydrogen as carrier gas D. Mathura) Center for Integrated Electronics, Electronics Manufacturing, and Electronic Media and The Howard P. Isermann Department of Chemical Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180
G-R. Yang and T-M. Lub) Center for Integrated Electronics, Electronics Manufacturing, and Electronic Media and Department of Physics, Rensselaer Polytechnic Institute, Troy, New York 12180 (Received 29 December 1997; accepted 17 April 1998)
A new method for depositing parylene-F (PA-F) thin films on silicon substrates has been explored. Hydrogen has been used as a carrier gas along with liquid precursors, dibromotetrafluoro-p-xylene and 1,4-bis(trifluoromethyl)benzene, to deposit PA-F. The properties of this film have been compared with the films obtained by the Gorham dimer method and the liquid precursor method using FTIR, XPS, and XRD. The PA-F films deposited by the dimer or liquid precursor acquired some kind of microcrystallinity on annealing. However, the PA-F films deposited in the presence of hydrogen were amorphous on annealing. This property could be potentially exploited for application in microelectronic device fabrication.
I. INTRODUCTION
A great amount of work is being done on low dielectric constant polymers for integrated circuits. The two main polymer groups are polyimides (PI) and parylenes (PA).4,5 Parylenes have a lower dielectric constant (2.4–3.3), as opposed to polyimides (3.0–3.5). Among the parylene family, parylene-F (PA-F) has the lowest dielectric constant of 2.4. In order to maintain compatibility with conventional techniques used in microelectronic device fabrication, a vacuum deposition method has been employed to fabricate the PA-F polymer film. This approach has its advantages over the spin coating method, where filling small vias becomes difficult with the scaling down of microelectronic devices. The conventional method for depositing poly-a, a 0 , 00 a , a 000 -tetrafluoro(para-xylylene), parylene-F, is called the dimer method and was given by Gorham.1,2 In this method, 1, 1, 2, 2, 9, 9, 10, 10-octafluoro [2.2] paracyclophane (dimer) was used as a precursor and underwent thermolytic scission at about 720–730 ±C to produce the highly reactive monomeric a, a, a 0 , a 0 -tetrafluorop-xylylene (monomer) which readily polymerized on the surface of the substrate at 220 to 235 ±C. PA-F films produced by the dimer method have a dielectric constant of about 2.4 and an impurity level of 5 at. % O as determined by x-ray photoelectron spectroscopy (XPS). In addition, the dimer is not commercially produced. Synthesizing it is an expensive and time-consuming process.
a)
Current address: GE Plastics, Research and Development, 12/11, Waterford, New York 12188. b) Address correspondence to this author. 246
http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 1, Jan 1999
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An alternative to the above method for depositing PA-F films is using liqui
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