SiO2 etching using inductively coupled plasma

Silicon dioxide etching in an inductively coupled plasma (ICP) using a multispiral coil (MSC) has been studied on the basis of CFx (x = 1, 2) radical measurement employing a laser-induced fluorescence (LIF) technique. Fundamental radical behavior in the MSC-ICP has been investigated in relation to the SiO2 etching characteristics for CF4, CHF3, and C4F8 gas chemistries. Moreover, two promising methods to achieve highly selective SiO2 etching, namely, chamber wall heating and the pulse modulation technique, have been examined for a CHF3/C4F8 plasma. It was found that chamber wall heating of up to 100 °C leads to a drastic increase in the SiO2 selectivity to Si, accompanied by an increase in the radical densities. A further increase in the selectivity of SiO2 to approximately 45 was realized by pulse modulation, whereby the CF2 radical density increases with shortening of the modulation period to 20 μs. The resultant high selectivity is discussed in relation to the radical composition change through dissociation and extinction processes, controlled by the chamber wall heating and pulse modulation techniques.