Physical characterization of Cu-Ni-P thin films aiming at Cu/Cu-Ni-P thermocouples

Abstract

Cu-Ni-P thin films have a high-thermoelectric power, which allows the fabrication of very sensitive heat-flux sensors based on planar technology. In this work, (100) silicon surfaces were pre-activated in a diluted hydrofluoric acid solution containing PdCl2 . Following, Cu-Ni-P thin films were chemically deposited using an alkaline chemical bath containing 15 g/l NiSO4 .6H2O; 0.2 g/l CuSO4 .5H2O; 15 g/l Na2 HPO2 .H2O and 60 g/l Na3 C6 H5O7 .2H2O at temperature of 80 ° C where NH4 OH was added until pH was 8.0. It was noteworthy that the stoichiometric percentages of Ni and Cu vary substantially for immersion times in the range of 1 to 3 min and they become almost stable at 50% and 35%, respectively, when the immersion time is higher than 3 min. In addition, the percentage of P remains almost constant around 17-18 % for all the immersion times studied. On the other hand, the sheet resistance also varies substantially for immersion times in the range of 1 to 3 min. Based on the surface morphology, smaller grains with size in the range of 0.02 to 0.1 μm are initially grown on the silicon surface and exposed regions of silicon without deposits are also observed for immersion times in the range of 1 to 3min. Therefore, the discontinuities and non uniformities of the films are promoting, respectively, the observed behaviours of sheet resistance and stoichiometry.