Electroless CoWP as a Diffusion Barrier between Electroless Copper and Silicon

Abstract

In this work, an electroless CoWP film deposited on a silicon substrate as a diffusion barrier for electroless Cu and silicon has been studied. Four different Cu 120 nm/CoWP/Si stacked samples with 30, 60, 75, and 100 nm electroless CoWP films were prepared and annealed in a rapid thermal annealing (RTA) furnace at 300°C to 800°C for 5 min. The failure behavior of the electroless CoWP film in the Cu/CoWP/Si sample and the effect of CoWP film thickness on the diffusion barrier properties have been investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and sheet resistance measurements. The composition of the electroless CoWP films was 89.4 at.% Co, 2.4 at.% W, and 8.2 at.% P, as determined by energy dispersive X-ray spectrometer (EDS). A 30 nm electroless CoWP film can prevent copper penetration up to 500°C, and a 75 nm electroless CoWP film can survive at least up to 600°C. Therefore, increasing the thickness of electroless CoWP films effectively increases the failure temperature of the Cu/CoWP/Si samples. The observations of SEM and TEM show that interdiffusion of the copper and cobalt causes the failure of the electroless CoWP diffusion barriers in Cu/CoWP/Si during thermal annealing.

Electroless Deposition of Nanolayered Metallic Coatings

“…In high pH bath with heat treatment films of Co-Fe-P, showed good soft magnetic properties. The magnetic properties of Co-W-P films have been studied by many authors [83][84]. Magagnin et al [85] have proposed that electroless cobalt-phosphorus acts as a metallization barrier for copper in lead-free soldering.…”

Barrier Integrity of Electroless Diffusion Barriers and Organosilane Monolayer against Copper Diffusion under Bias Temperature Stress

“…In previous research on electroless plated CoWP as a metal cap, the composition were as follows: Co, 91%; W, 3%; and P, 6% for one sample [24][25][26] and Co, 89.4%; W, 2.4%; and P, 8.2% for another sample. 27) It was reported that there were barrier properties of CoWP in 400 14) or 500 C 27) annealing. Compared with the previous reports, the W and P contents were lower than those in the previous reports.…”

Synthesis and characterization of electroless deposited Co–W–P thin films as diffusion barrier layer

“…The mechanism depended on the direct transformation of the tungstate anions WO 4 2− into tungstite cations WO 2 2+ . In alkaline solution, the tungsten citrate complex at the substrate surface dissociates with the formation of WO 2 2+ ion and this ion, in turn, is reduced to W. Reduction of the tungstate ions can be described by the following equation;…”

“…Electroless deposition of metal alloys has found numerous applications in advanced metallization technology for fabrication of conductive, magnetic, reflective, and decorative layers [3]. Recently, some studies have focused on the deposition of Co and its alloys due to the wide range of applications in aerospace and automotive component production, chemical synthesis and electronics [4].…”