Investigation Of Inductively Coupled Fluorocarbon Plasma And Etching Of SiO₂

SiO₂ is still used extensively as the dielecteic in the semiconductor industry and is etched by fluorocarbon plasmas. Though have long been studied, the etch mechanism have not been completely understood.By adjusting gas flow ratio R(R=[C4F8]/{[C4F8]+[Ar]}), source power and self bias, the etching of SiO₂ in an Ar+C4F8 inductively coupled plasma is carried out while the fluorocarbon plasma is monitored by optical emission spectroscopy(OES) and Langmuir probe. It is found that the SiO2 etching rate increases with the increase of both source power and self-bias voltage. As R increases, however, the variation of the etch rate is not monotonic, but the maximum value is located at R=8%. Provided that the reaction between gas-phase ions/radicals and fluorocarbon polymer on chamber/substrate surface contributes mainly to the production of C2 radical, the dependence of C2 emission intensity on gas flow ratio R is similar to that of the etch rate is explained. Based on the above analysis, the variation of etch profiles with etching conditions is investigated. The results indicate that the tapered etch profile and the photoresist branches are caused by fluorocarbon polymer layer together with the redeposited etch products on the sidewall, especially under larger R and higher self-bias voltage condition.