Plasma Kinetic Study of Silicon-Dioxide Removal with Fluorocompounds in a Plasma-Enhanced Chemical Vapor Deposition Chamber

Abstract

Plasma kinetics of silicon dioxide plasma cleaning is investigated with C2F6 and CF3CF2OCF=CF2 (perfluoroethyl vinyl ether, PEVE) in this work. Perfluorocompounds (PFCs) are widely used in the semiconductor industry, and they are known to have long atmospheric lifetimes and high global warming potentials (GWP) due to their chemical stability and large cross sections for infrared radiation absorption. The silicon dioxide (SiO2) cleaning process in a plasmaenhanced chemical vapor deposition (PECVD) chamber is known to be the largest PFC emission source for the semiconductor industry. Silicon-dioxide removal rates by surface reactions in plasmas were measured in the temperature range from room temperature to 400 C by using laser interferometry, and the fluorine density was determined by using an optical emission spectroscopy (OES) actinometry technique. The ion density and the ion energy were determined by using an impedance analysis and an equivalent circuit model. The activation energy was determined from Arrehenius plot to be 0.163 eV and 0.169 eV for C2F6 and PEVE plasmas, respectively, in the PECVD chamber cleaning condition. It is shown here that silicon-dioxide removal rate is linearly proportional to the fluorine concentration for the PECVD chamber cleaning condition of 300 400 C and that the removal rate depends on the ion flux and the ion energy below 100 C. The combined etch rate model is suggested to explain this temperature dependence in this work. From this plasma kinetic study, we can conclude that the atomic fluorine concentration is the dominant factor in silicon-dioxide removal for the PECVD chamber cleaning condition.