Effect of source frequency and pulsing on the SiO sub(2) etching characteristics of dual-frequency capacitive coupled plasma

A SiO sub(2) layer masked with an amorphous carbon layer (ACL) has been etched in an Ar/C sub(4)F sub(8) gas mixture with dual frequency capacitively coupled plasmas under variable frequency (13.56-60 MHz)/pulsed rf source power and 2 MHz continuous wave (CW) rf bias power, the effects of the frequency and pulsing of the source rf power on the SiO sub(2) etch characteristics were investigated. By pulsing the rf power, an increased SiO sub(2) etch selectivity was observed with decreasing SiO sub(2) etch rate. However, when the rf power frequency was increased, not only a higher SiO sub(2) etch rate but also higher SiO sub(2) etch selectivity was observed for both CW and pulse modes. A higher CF sub(2)/F ratio and lower electron temperature were observed for both a higher source frequency mode and a pulsed plasma mode. Therefore, when the C 1s binding states of the etched SiO sub(2) surfaces were investigated using X-ray photoelectron spectroscopy (XPS), the increase of C-F sub(x) bonding on the SiO sub(2) surface was observed for a higher source frequency operation similar to a pulsed plasma condition indicating the increase of SiO sub(2) etch selectivity over the ACL. The increase of the SiO sub(2) etch rate with increasing etch selectivity for the higher source frequency operation appears to be related to the increase of the total plasma density with increasing CF sub(2)/F ratio in the plasma. The SiO sub(2) etch profile was also improved not only by using the pulsed plasma but also by increasing the source frequency.