Theoretical and Experimental Analysis of the Low Dielectric Constant of Fluorinated Silica

Abstract

Fluorinated silica has a dielectric constant lower than that of F-free SiO2 and is a potential interlayer dielectric. We investigate the F-doped SiO2 with ab-initio modeling and various characterization techniques searching to explain the dielectric constant reduction. FTIR transmission and spectroscopic ellipsometry give us information about the ionic and electronic contributions to ε. Nuclear reaction analysis and Auger spectrometry measure F composition. XPS and FTIR provide information on the atomic structure of the film. We use several cells of cristobalite to model fluorinated silica using the electronic structure theory. The ground state geometry, vibrational density of states, electronic band structure, and Born effective charges are analyzed. The calculations suggest that it is the ionic component of the dielectric constant that is mostly effected by the F incorporation.

High strength, low dielectric constant fluorinated silica xerogel films

“…͓DOI: 10.1063/1.1418267͔ Fluorinated silica xerogel films have aroused interest as interlayer dielectrics due to their compatibility with largescale integration and decreased dielectric constants. [1][2][3][4] Fluorine doping of silica films most often employs plasmaenhanced chemical vapor deposition ͑PECVD͒ of silica with a fluorine source ͑e.g., CF 4 , SiF 4 ͒ or PECVD of triethoxyfluorosilane ͑TEFS͒. [2][3][4] Previous studies have shown fluorine distorts Si-O rings and increases silica tetrahedral framework formation, limiting the lattice polarizability and thus decreasing the dielectric constant.…”

“…[1][2][3][4] Fluorine doping of silica films most often employs plasmaenhanced chemical vapor deposition ͑PECVD͒ of silica with a fluorine source ͑e.g., CF 4 , SiF 4 ͒ or PECVD of triethoxyfluorosilane ͑TEFS͒. [2][3][4] Previous studies have shown fluorine distorts Si-O rings and increases silica tetrahedral framework formation, limiting the lattice polarizability and thus decreasing the dielectric constant. 4,5 Fourier transform infrared ͑FTIR͒ spectrophotometry studies have shown that the upward shifting of Si-O stretching modes correlates with increases in the fluorine content and decreases in the dielectric constant.…”

“…[2][3][4] Previous studies have shown fluorine distorts Si-O rings and increases silica tetrahedral framework formation, limiting the lattice polarizability and thus decreasing the dielectric constant. 4,5 Fourier transform infrared ͑FTIR͒ spectrophotometry studies have shown that the upward shifting of Si-O stretching modes correlates with increases in the fluorine content and decreases in the dielectric constant. 3,6 Such effects were also found to be due not only to decreasing ionic polarization, but also to a decrease in orientational polarization attributed to Si-OH bonding, which also decreased as a result of fluorine doping.…”