Dependence of Etch Selectivity of SiO2 Etching on the Axial Magnetic Field in ICP

초록

Effects of time-varying axial magnetic field added to an ICP have been studied in terms of plasma characteristics and etching performances. The magnetic field in the acial direction is generated by a pair of Helmholtz coil, and the time-varying field by flowing time-varying current to the coil. In this work, the etch selectivity of SiO2 over photoresist is investigated in C4F8/Ar plasma. The frequency of the axial magnetic field is found to affect the etch selectivity. We have measured the CFx+ (x=1-3) ion density and its energy distribution function using QMA with energy analyzer. Densities of F atom and CFx(x=1-3) radicals are also measured by Apparent Mass Spectrometer as a function of the magnetization frequency. XPS analysis of fluorocarbon polymer formed on oxide surface during etching shows that fluorine content in the polymer is varies with the magnetization frequency. It is found that thicker fluorocarbon pilymer films are depositied at higher CF2 radical intensity in the plasma, and that faster oxide etching is observed at higher CFx+ ions in the plasma. A model that describes the role of fluorine in fluorocarbon polymers in oxide etching is proposed, and the conditions where higher etch selectivity of oxide to photoresist are described.