Controlling ion/radical ratio and monoatomic/polyatomic radical ratio in a process plasma provides improved processing performance during inductively-coupled plasma and/or helicon wave plasma processing of substrate materials. In a plasma processing method employing inductively coupled plasma, high frequency current to a high frequency antenna is intermittently supplied in a controlled manner to control the state of gas dissociation to promote formation of polyatomic radicals. In a plasma processing method employing helicon wave plasma, current supplied to a magnetic field generator is intermittently supplied in a controlled manner to promote formation of ions. In a preferred method both the high frequency current and magnetic field generating current are varied in a controlled manner to provide a variable plasma composition, i.e., radical rich plasma or ion-rich plasma, as desired, for improved plasma processing especially improved selective anisotropic dry etching at high etch rate.