Effect of Heat-Treatment on Properties of Electroless-Deposited Nickel-Molybdenum-Phosphorus Alloy Films

The film properties and the heat change properties of new electroless plated Ni-Mo-P alloy films, which were deposited from a newly developed simpler bath with direct addition of Na₂Mo0₄, were investigated as a basis for developing new functional thin film. Both amorphous and crystallized Ni-Mo-P alloy films were prepared by simply controlling the Na₂Mo0₄ concentration in the baths. The maximum molybdenum content of 14.9 atom percent (22.3 weight percent) was attained at a Na₂Mo0₄ concentration of 0.020 mol dm^-3, and the films having high resistivity and high thermal stability were obtained. The formation of solid solution between Ni Matrix and codeposited Mo was indicated on the basis of comparison with bulk Ni-Mo alloy. The amorphous Ni-Mo-P alloy film had much better thermal stability than did the amorphous Ni-P alloy film. In the case of crystallized Ni-Mo-P alloy film, the small grain size of electroless Ni-Mo-P alloy film was maintained even after heat-treatment up to 400°C. The crystallization process of the amorphous and crystallized Ni-Mo-P alloy films by heat-treatment was quite different from that of an ordinary electroless Ni-P alloy film. Three structural changes resulting from heat-treatment were observed in electroless Ni-Mo-P alloy films, namely, the formation of Ni₃P, the crystallization of Ni-Mo alloy, and the transformation of Ni-Mo alloy. A schematic model of Ni-Mo-P alloy films composed of two phases or zones, namely, the Ni-Mo and Ni-Mo-P, was proposed to explain the heat change properties of Ni-Mo-P alloy films.