Effect of Time-varying Axial Magnetic Field on Photoresist Ashing in an Inductively Coupled Plasma

초록

Time-varying axial magnetic field coupled with ICP has been found to provide more uniform and higher density plasma with lower electron temperature. Weak axial magnetic fielc can be obtained by a pair of current flowing Helmholtz coils attached to the chamber. This scheme has been applied to etch SiO2 and silylated photoresist, where processing pressures are below 50 mTorr and ions are major reaction species. In this work, this method is applied to photoresist ashing, where processing pressure is usually higher than 1 Torr and down stream oxygen radicals are important species. It is found that axial magnetic field improves the ashing rate by 25% and uniformity of 4% over 8" wafer, and that the optimum frequency of the magnetic field is 60Hz. Optical emission spectroscopy is used to characterize the effect of the magnetic field. Effect of aluminum baffle inserted between plasma and wafers is also investigated in this system.