RESIDENCE TIME EFFECTS ON SIO2 SI SELECTIVE ETCHING EMPLOYING HIGH-DENSITY FLUOROCARBON PLASMA/

The residence time effects on SiO2 etching characteristics using induc tively coupled plasma of C4F8 alone were first studied in the range fr om 6 to 300 ms. It was then found that SiO2 and Si etch rates were min imum at a residence time of 25 ms, at which the CF1+ ion density and t he fluorocarbon polymer deposition rate measured at 130 degrees C beca me maximum. From this good correspondence, the SiO2 etching was consid ered to follow a reaction model where the CF1+ ions might contribute t o the polymer deposition, thus suppressing the SiO2 etching, and where the dominantly observed CF1+ ions could etch SiO2 on the assumption o f elevated SiO2 surface temperature due to the ion bombardment. Next, in the condition of short residence times (<25 ms), Ar was added to C4 F8 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 res idence time of 10 ms the SiO2 etch rate continuously increased with th e Ar concentration up to a maximum etch rate of 0.4 mu m/min for 90% A r addition. Various plasma diagnostics demonstrated that the 90% Ar ad dition resulted in an increase of the CFx+ (x=1-3), C+, and Ar+ ion de nsities, in contrast to a decrease of the CF3 radical density. Metasta ble Ar atoms as well as highly elevated electron temperature are consi dered to be responsible for the increasing ion species. Consequently S iO2/Si contact hole features with 0.18 mu m opening and 2 mu m depth w ere successfully fabricated employing the 90% Ar/C4F8 mixture at a res idence time of 10 ms. The He addition has also been investigated and s howed similar changes in plasma characteristics to those observed for Ar addition, but the ''etch stop'' occurred. This probably resulted fr om the poor sputtering effect of He+ ions due to their light mass. (C) 1998 American Vacuum Society.