Comparison of Electroless Ni-P and Co-W-P Diffusion Properties Against GaAs Substrate

The thermal stability of electroless nickel-phosphorus (Ni-P) film and cobalt-tungsten–phosphorus (Co-W-P) film deposited on GaAs substrate was investigated. X-ray photoelectron spectroscopy and x-ray diffraction measurements indicated that the Ni-P film changed from amorphous to crystalline by annealing at 240°C for 1 h due to the diffusion of Ni into the GaAs substrate and the increase in P concentration in the Ni-P film. On the other hand, the crystallinity of the Co-W-P film did not change by annealing at 240°C for 1 h. Cross-sectional observation showed that the thickness of the crystallized Ni-P film did not change from 3 to 1000 h of high-temperature storage at 270°C, and no void was observed in the Ni-P film. Migration of Ni atoms could be suppressed by the crystallization of the Ni-P film. On the other hand, voids were formed in the Co-W-P film after high-temperature storage at 270°C for 100 h. Since the Co-W-P film consists of nanoscale crystalline and amorphous phases, atoms diffuse from the amorphous portion to the GaAs substrate.