Structire, Properties, and Process Characteristics of Low-K Materials Prepared by PECVD
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H. Komiyama*** * Department of Metallurgy, University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan, [email protected] ** Department of Electrical Engineering, Stanford University, *** Department of Chemical System Engineering, University of Tokyo **** Department of Electronic Engineering, University of Tokyo ***** Division of Electrical & Computer Engineering, Yokohama National University ABSTRACT Low dielectric constant F-doped silicon oxide films (SiO:F) can be prepared by adding fluorine source, like as CF4' to the conventional PECVD processes. We could obtain SiO:F films with dielectric constant as low as 2.6 from the reaction mixture of SiH 4/N2 O/CF. The structural changes of the oxides were sensitively detected by Raman spectroscopy. The three-fold ring and network structure of the silicon oxides were selectively decreased by adding fluorine into the film. These structural changes contribute to the decrease ionic polarization of the film, but it was not the major factor for the low dielectric constant. The addition of fluorine was very effective to eliminate the Si-OH in the film and the disappearance of the Si-OH was the key factor to obtain low dielectric constant. A kinetic analysis of the process was also performed to investigate the reaction mechanism. We focused on the effect of gas flow rate, i.e. the residence time of the precursors in the reactor, on growth rate and step coverage of SiO:F films. It revealed that there exists two species to form SiO:F films. One is the reactive species which contributes to increase the growth rate and the other one is the less reactive species which contributes to have uniform step coverage. The same approach was made on the PECVD process to produce low-k C:F films from C2F4' and we found ionic species is the main precursor to form C:F films.
INTRODUCTION With diminishing dimension of device, the RC time delay is now a significant issue in VLSIs [I]. Low dielectric constant and low resistive materials are the solution for this problem, and now many researchers have studied low dielectric constant material like as F-doped SiO 2 (SiO:F) and fluorinated amorphous carbon (a-C:F) films. The authors have reported that it is possible to have SiO:F films with the dielectric constant of 2.6 by adding CF 4 as the fluorine source to the SiH 4/N2 0 chemistry [2-4]. We have studied the decrease mechanism of dielectric constant and structural change of F-doped SiO 2 films, focusing on the frequency dependency of the dielectric constant. We found that the key to have low dielectric constant SiO:F film is to suppress the Si-OH bond formation by incorporating Si-F bond instead of it. Preparation of TeflonT" liked amorphous carbon films by glow discharge of C2 F4 gas was also performed to have dielectric constant of 2.0. The structure and the film properties of a-C:F film was almost independent to the depostion conditions. Macroscopic kinetic studies by changing mainly the residence time (an external controllable parameter) in plasma region without consideration
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