Comparison of C2F6 and FASi-4 as fluorine dopant sources in plasma enhanced chemical vapor deposited fluorinated silica glass films

Abstract

Fluorine doping of silicon dioxide films in tetraethylorthosilicate (TEOS)-based plasma enhanced chemical vapor deposition (PECVD) processes was investigated using two fluorine dopant sources, C2F6 and 1,2 bis[methyldifluorosilyl]ethane (FASi-4). Much as TEOS-based undoped silica glass (USG) films display improved step coverage over silane-based USG films, it was suspected that fluorinated silica glass (FSG) films deposited using the relatively new TEOS-based fluorine source FASi-4 might have improved gap fill capabilities as compared to FSG films deposited using gas-based C2F6 fluorine sources. The physical properties and intermetal gap filling capabilities of FSG films deposited using FASi-4 as a fluorine dopant source were compared with the properties of FSG films deposited using C2F6 as a fluorine source. Fluorine dopant levels in the films were found to be linear functions of C2F6TEOS and FASi-4yTEOS ratios. The RI, film stress, and gap fill capability were found to be strongly dependent on the Si–F content in the film regardless of dopant source reagents. Improved gap fill characteristics were observed in films doped with FASi-4 at a given Si–F/Si–O% as compared to C2F6-based FSG films. Dopant source dependence of doping characteristics, physical properties, and gap filling capability of FSG films is reported.