Theoretical and Experimental Analysis of the Low Dielectric Constant of Fluorinated Silica
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THEORETICAL AND EXPERIMENTAL ANALYSIS OF THE LOW DIELECTRIC CONSTANT OF FLUORINATED SILICA A. DEMKOV*, S. ZOLLNER*, R. LIU*, D. WERHO*, M. KOTTKE*, R.B. GREGORY*, M. ANGYAL*, S. FILIPIAK*, G.B. ADAMS** *Motorola Semiconductor Products Sector, Mesa, AZ **Department of Physics, Arizona State University, Tempe, AZ 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. INTRODUCTION Interest in insulating films with low static dielectric constants ε (or εDC, or k) increases, as transistor gate lengths shrink below 0.25 µm, [1]. The parasitic capacitance between metal lines causes signal delay, but could be reduced with these so-called low-k dielectrics. whereas The SEMATECH roadmap calls for materials with ε
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