Reactive ion etching of polyimidesiloxanes in fluorine-containing discharges

There is great interest in polyimides as dielectric insulators in high density circuits due to their high thermal stability and excellent dielectric properties. The newly developed polyimidesiloxanes (SIMs) offer several additional advantages over conventional polyimides in applications to microelectronic packaging. However, there are only a few studies on the reactive ion etching (RIE) behavior of SIMs in fluorine-containing discharges. Previously reported RIE results of SIMs showed a very low etching rate in a pure oxygen plasma. In this study, we investigated the etching behavior of SIMs in discharges of CF4/O2 and SF6/O2 mixtures. Actinometric optical emission spectrometry was used to monitor the relative densities of F and O atoms. The highest etching rates were found in SF6/O2 RIE due to the greatly increased concentrations of both F and O atoms. The maximum etching rate in each mixture appeared near the same IF(703.5 nm)/Io(844.6 nm) ratio, which is directly related to the F to O atom concentration ratio. The IF/Io ratio for the maximum etching rate was found to be invariant despite the different etching conditions of reactive gases, loading effects, and vacuum conditions. By comparing the etching rates of nonsiloxane polyimide and SIMs with different siloxane content in various discharges, we observed preferential etching behavior of SIMs in fluorine-rich environments.