Abstract
A NiMoP film which may potentially be used as barrier/seed layer for Cu interconnect was successfully formed via electroless deposition atop SiO2. Four different wet processes were tried to activate the surface before electroless deposition. In addition, material properties including the crystal structure, deposition rate, composition and the electrical resistivity of NiMoP were investigated by scanning electron microscope (SEM), Auger electron microscope (AES), x-ray diffraction (XRD), 4-point probe, and surface profilometer (Alpha-step). NiMoP film of different compositions were obtained. Ni89Mo2P9 with nano-crystalline structure has the highest resistivity due to enriched P content while Ni88Mo9P3 has the lowest value among all. The seed layer and barrier layer functions of NiMoP were verified after Cu electrodeposition and the study of secondary ion mass spectroscopy (SIMS). Thermal cycles were then applied to Cu/NiMoP/SiO2 specimen in a nitrogen ambient at 200, 300, 400, and 500℃ respectively. Both the lattice and grain boundary diffusion of Cu in NiMoP was investigated by SIMS. The diffusion kinetics of each composition was discussed. Mo-rich Ni88Mo9P3 shows good barrier function in comparison with conventionally used TaN and possesses lower electrical resistivity. This finding indicates that NiMoP successfully combines the functions of seed layer and barrier layer, providing a potential alternative for conventional TaN/Cu seed couple. Next, a novel activator based on electrografting was developed for the electroless deposition of NiMoP. An aqueous solution containing 4-vinylpyridine (4VP) was prepared for electrografting of P4VP on SiO2/Si substrate despite the insulating property of the upper oxide layer. The identity and morphology of P4VP film was then investigated by X-ray Photoelectron Spectroscopy (XPS) and Scanning Probe Microscopy (SPM). In addition, when Pd ions were present in the solution, Pd was found to be incorporated within the electrografted P4VP matrix and could serve as an efficient activator for electroless deposition without further pretreatment. Moreover, the formation of Si-O-C bonding and Pd-P4VP complex were both confirmed by the chemical shift of several elements. The thickness control, uniformity and adhesion of the NiMoP deposit can all be improved by applying this novel activator. According to the result, a cost-effective all-wet process for fabricating Cu interconnect structure can thus be established by integrating Cu electrodeposition and electroless deposition of NiMoP with the aid of Pd-P4VP activator.