Residence time effects on SiO2/Si selective etching employing high density fluorocarbon plasma

The residence time effects on SiO2 etching characteristics using inductively coupled plasma of C4F8 alone were first studied in the range from 6 to 300 ms. It was then found that SiO2 and Si etch rates were minimum at a residence time of 25 ms, at which the CF1+ ion density and the fluorocarbon polymer deposition rate measured at 130 °C became maximum. From this good correspondence, the SiO2 etching was considered to follow a reaction model where the CF1+ ions might contribute to the polymer deposition, thus suppressing the SiO2 etching, and where the dominantly observed CF3+ ions could etch SiO2 on the assumption of elevated SiO2 surface temperature due to the ion bombardment. Next, in the condition of short residence times (<25 ms), Ar was added to C4F8 in order to allow Ar+ ions to remove the fluorocarbon polymer film that is responsible for the reduction of the SiO2 etch rate. For a residence time of 10 ms the SiO2 etch rate continuously increased with the Ar concentration up to a maximum etch rate of...