Angular dependences of SiO2 etch rates at different bias voltages in CF4, C2F6, and C4F8 plasmas

Abstract The angular dependences of SiO 2 etch rates at different bias voltages for in CF 4 , C 2 F 6 , and C 4 F 8 plasmas were investigated using a Faraday cage system. When the bias voltage was − 400 V, the normalized etch yields (NEYs) reached a maximum at 70° in CF 4 and C 2 F 6 plasmas, while they decreased monotonically with ion-incident angle in a C 4 F 8 plasma. This was because the thickness of the steady-state fluorocarbon film formed on the SiO 2 surface was minimized at an ion incident angle of 70° in CF 4 and C 2 F 6 plasmas, while much thicker fluorocarbon films were deposited in a C 4 F 8 plasma. When the bias voltage was as high as − 1200 V, the thicknesses of the steady-state fluorocarbon films were very thin (less than 2 A) and nearly unchanged at all ion-incident angles for CF 4 and C 2 F 6 plasmas, resulting in nearly the same shape of the NEY curves. In a C 4 F 8 plasma, the NEY showed a maximum at an ion-incident angle of 50° because the thickness of the steady-state fluorocarbon film was minimized at this angle.