Counterbore dielectric plasma etch process particularly useful for dual damascene

Abstract

A dielectric etch process particularly applicable to forming a dual-damascene interconnect structure by a counterbore process, in which a deep via is etched prior to the formation of a trench connecting two of more vias. A single metallization fills the dual-damascene structure. The substrate is formed with a lower stop layer, a lower dielectric layer, an upper stop layer, and an upper dielectric layer. For example, the dielectric layers may be silicon dioxide, and the stop layers, silicon nitride. The initial deep via etch includes at least two substeps. A first substep includes a non-selective etch through the upper stop layer followed by a second substep of selectively etching through the lower dielectric layer and stopping on the lower stop layer. The first substep may be preceded by yet another substep including a selective etch part ways through the upper dielectric layer. For the oxide/nitride compositions, the selective etch is based on a fluorocarbon and argon chemistry, preferably with a lean etchant of CHF,combined with a polymer former, such as C,F,, C,F,, or CH,F,, and the non-selective etch includes a fluorocarbon or hydrocarbon, argon and an oxygen-containing gas, such as CO. The counterbore etch is preferably performed in a high-density plasma reactor which allows the plasma source region to be powered separately from a sheath bias located adjacent to the wafer pedestal.