Selective Cu native oxide removal via in situ N2 plasma and ultrathin SiN capping: A stable alternative to wet chemical and Ar plasma treatments

The removal of native copper oxide and the preservation of a clean, smooth Cu surface are critical requirements for surface preparation in advanced interconnect technologies and heterogeneous integration processes. This work introduces a novel surface treatment combining N2 plasma activation with immediate in situ deposition of an ultrathin SiN capping layer, and benchmarks it against established wet chemical (HCl, H2SO4, CH3COOH) and Ar plasma + NH4OH approaches for removing native oxide while retaining a low-roughness morphology. Each treatment is assessed through grazing incidence x-ray diffraction (GIXRD) and atomic force microscopy. Quantitative GIXRD analysis shows that N2 plasma with SiN capping and H2SO4 both achieve near-complete oxide removal (98.7% and 96.0% reduction, respectively), but H2SO4 acts as an aggressive nonselective etchant that substantially increases surface roughness (3.51 nm RMS), while the plasma + SiN route removes the oxide selectively, preserves a low surface roughness (0.75 nm RMS), and prevents reoxidation for at least ten days. To the best of our knowledge, the use of an ultrathin SiN cap for Cu surface preservation in this context has not been reported before, making this approach a unique and original contribution of this study. The study also evaluates the influence of post-treatment exposure conditions. These findings identify effective cleaning and passivation routes for Cu surface preparation in advanced interconnect processing, where chemical cleanliness, low surface roughness, and atmospheric stability are key requirements.