We investigated the effects of 13.56 MHz radio frequency (rf) power as a medium frequency power on the plasma characteristics and etch properties of an amorphous carbon layer (ACL) and SiO 2 , using Ar/C 4 F 6 /O 2 gas mixtures in a capacitively coupled plasma (CCP) system operated with pulsed superimposed triple-frequency power of 60 MHz (source)/13.56 MHz (bias)/2 MHz (bias). Compared to the dual frequency rf power of 13.56 MHz (400 W)/2 MHz (900 W) or 60 MHz (400 W)/2 MHz (900 W), the use of triple-frequency rf power of 60 MHz/13.56 MHz/2 MHz (900 W) showed a better anisotropic SiO 2 etch profile, with the higher etch selectivity of SiO 2 over the ACL. We observed the best SiO 2 etch characteristics when the rf powers of 60 MHz and 13.56 MHz were set as 60 MHz (200 W)/13.56 MHz (200 W). In addition, when we varied the pulse duty percentage of 13.56 MHz rf power from 25∼100% (continuous wave (CW)), while keeping the rf powers of 60 MHz/13.56 MHz/2 MHz at 200 W/200 W/900 W, respectively, and while maintaining the pulse duty percentage of 60 MHz and 2 MHz at 50%, the use of the synchronized pulse on/off condition (i.e., the use of 50% duty percentage of 13.56 MHz) also showed the best etch characteristics. The best SiO 2 etch characteristics and the highest etch selectivity of SiO 2 over the ACL (observed for both rf power ratios of 60 MHz (200 W)/13.56 MHz (200 W), and for the triple-frequency pulsing with the synchronized pulse on/off) were related to the higher CF x /F ratios, which increased the fluorocarbon polymer passivation on the ACL surface and SiO 2 sidewall during etching.
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