Fabrication of potential NiMoP diffusion barrier/seed layers for Cu interconnects via electroless deposition

Abstract

Potential NiMoP barrier/seed layers for Cu interconnects have been successfully formed by electroless deposition on SiO 2 . Four different wet processes were attempted to activate the surface before electroless deposition. Material properties including the crystal structure, deposition rate, composition, and electrical resistivity of NiMoP layers were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), Auger electron spectroscopy, x-ray diffraction (XRD), four-point probe, and surface profilometry (Alpha-step). In this study, different compositions of NiMoP films have been obtained. Ni 89 Mo 2 P 9 with nanocrystalline structure has the highest resistivity due to enriched P content, while Ni 88 Mo 9 P 3 has the lowest value among the compositions considered in this study. The seed layer and the barrier layer functions of NiMoP were verified by direct Cu electrodeposition and secondary ion mass spectroscopy (SIMS).

Surface modifications of aluminum alloy 5052 for bipolar plates using an electroless deposition process

“…According to the SEM observation of the Ni-Mo-P deposits, the surface roughness, the granular size, and the thickness of these deposits decreased drastically with increasing concentration of Na 2 MoO 4 , which supplies the Mo element to the Ni-Mo-P alloys, in the electroless bath. This phenomenon may be attributable to the presence of MoO 4 2− in the electroless solution [18,19]. In this experiment, the anodic reaction is the oxidation of H 2 PO 2 2− , which is a reducing agent and can be catalyzed to release electrons in the electroless solution for producing the Ni-Mo-P deposits.…”

“…In this experiment, the anodic reaction is the oxidation of H 2 PO 2 2− , which is a reducing agent and can be catalyzed to release electrons in the electroless solution for producing the Ni-Mo-P deposits. The MoO 4 2− appearing in the solution would cause an inhibiting effect on the oxidation of H 2 PO 2 2− , because MoO 4 2− would adsorb on the surface of the substrate [18,19]. In consequence, the catalytic reaction of Ni would be retarded and the deposition rates of Ni-Mo-P alloys would be significantly reduced.…”

“…On the contrary, lower concentration of OH − will be advantageous to the reaction of P reduction. In other words, the basic solution condition is helpful to the reaction of Ni and Mo reduction, and unfavorable to the precipitation of P [18,19]. Table 2 shows the composition percentage (wt.%) of Ni, Mo, and P detected by ICP-AES for the Ni-Mo-P deposits produced at the pH values of 7, 8, and 9.…”

“…It has been pointed out that the long-term corrosion resistance of Ni-Mo-P alloys can be remarkably improved by forming dense Mo oxide films on the deposit [23,25]. Moreover, the passive Mo element would accumulate on the grain boundaries of the Ni-Mo-P coating and result in a stuffing effect [18,26], which prevents the corrosion media and the metal ions from diffusing via grain boundaries. Therefore, the Ni-Mo-P deposit has better long-term corrosion resistance in a 0.5 M H 2 SO 4 environment.…”

“…Recently, some of the commercial electroless Ni-based deposits, such as Ni-P and Ni-B alloys, are extensively employed as coatings for applications in electronic or chemical production due to their superior corrosion resistance and electric conductivity. Moreover, Ni-P deposits alloyed with refractory metals, such as molybdenum, can improve the thermal stability of the alloys [18,19]. Therefore, Ni-Mo-P coatings have a good potential for the applications in bipolar plates.…”