Control of reactive plasmas for low-k/Cu integration

We proposed models for controlling surface reactions during etching of SiOCH and organic material. The etch rate of each material can be determined by the balance between the total atom fluxes of O, C, F, N, and H that were supplied from both the plasma and the etched material to the reactive layer. Low-k films (SiOCH, porous SiOCH, and organic material) have narrow process windows for obtaining good etching properties, such as selectivity, because the polymer and reactive layers on these films can be changed by only slight changes in the plasma parameters. Therefore, the partial pressure and dissociation of parent gas molecules in fluorocarbon or N–H plasma as well as plasma–wall interaction must be controlled. To create highly reliable interconnects, the interfaces between the metal and low-k must be optimized during the etching of stopper material and ashing. The surface of Cu is very reactive, the remaining F induces degradation of Cu. SiOCH can easily be oxidized during ashing processes, and the adsorption of H2O on damaged SiOCH causes interconnect failure during electrical tests. To suppress problems in the etching and ashing processes, the balance of the total atom fluxes should be quantitatively and instantaneously controlled to the optimum point for each material.