ROLE OF STEADY-STATE FLUOROCARBON FILMS IN THE ETCHING OF SILICON DIOXIDE USING CHF3 IN AN INDUCTIVELY-COUPLED PLASMA REACTOR

It has been found that in the etching of SiO2 using CHF3 in an inducti vely coupled plasma reactor of the planarized coil design, a thin stea dy state fluorocarbon film can play an important role in determining t he rate of etching. This etching is encountered as the amount of bias power used in the SiO2 etching process is increased, and a transition from fluorocarbon film growth on the SiO2 to an oxide etching rate whi ch is consistent with reactive sputtering theory is made. The observed presence of an intermediate region where etching occurs, although a s teady state fluorocarbon film suppresses the etch rate from that expec ted for a reactive sputtering process, has been referred to as the flu orocarbon suppression regime. This work demonstrates the role of the s teady state fluorocarbon film present on silicon dioxide during etchin g within the fluorocarbon suppression regime. X-ray photoelectron spec troscopy studies of the surfaces of partially etched SiO2 have shown a thinning of this film with increasing rf bias power, as well as a dec rease in the fluorine content of the surface film as a function of inc reasing rf bias power. We have found that slight variations in the fil m thickness, on the order of 1 nm, can result in large variations, app roximately 400 nm/min, in the silicon dioxide etch rate. The presence of the film within the suppression regime appears to be due to the ove rwhelming polymerization ability of high density plasmas, coupled with the inability of the oxide to react sufficiently with the total fluor ocarbon particle flux in order to completely remove this film. For thi s reason these types of reactors exhibit a regime where oxide etching occurs in the presence of a surface film. The film appears to be direc tly responsible for the observed suppression of the oxide etch rate fr om that expected for a reactive sputtering process by dissipating the bombarding ion energy, and thereby suppressing the energy flux arrivin g at the oxide surface. (C) 1997 American Vacuum Society.