Ion energy control in reactive ion etching using 1-MHz pulsed-DC square-wave-superimposed 100-MHz RF capacitively coupled plasma

For the precise control of the ion energy in reactive ion etching (RIE), a 1-MHz pulsed-direct current (DC) square-wave-superimposed (p-DCS) 100-MHz radio frequency (RF) capacitively coupled plasma (CCP) is studied and compared with a 13.56- and 100-MHz dual-RF-superimposed (DFS) CCP. The proposed CCP is applied in RIE for sub-32-nm node etching of spun-on-carbon using H2-based gas at 2.66 Pa and 1200 W of 100-MHz RF power. A minimum critical dimension shift of 3 nm is achieved at high etch rates in p-DCS CCP using an optimized square-wave voltage of −750 V, compared with a corresponding shift of 9 nm in DFS CCP using 400 W of 13.56-MHz RF power. Because the maximum of the ion energy distribution (IED) is controlled by the square-wave voltage and more than 70% of the total ion flux is concentrated in a narrow range around the maximum ion energy, the CCP offers precise control of the IED, which is effective in the RIE of the fine-patterned devices.