Electrolyte Considerations of Electrodeposited Ni-W Alloys for Microdevice Fabrication

Abstract

Electrodeposited systems that contain gas evolving side reactions, such as NiW, can be problematic for deep micro-recessed electrodes. A limiting factor for the adaptability of conventional plating baths to deep recess plating is the variance in hydrodynamic conditions. For Ni-W electrodeposition in citrate-ammonium electrolytes, buffering capacity and pulse plating has been considered to circumvent local pH rises accompanied by the side reaction. Based on simulated solubility data and determined buffer capacity the following composition for Ni-W electroplating was proposed: NiSO4 – 0.2 M; Na3Citr – 0.5 M; Na2WO4 – 0.4 M; Na2CO3 – 0.5 M; NH3 water – 1.2 M; t = 70 °C; pH 8.5 – 9; j = 10 – 60 mA cm–2 for alloys containing 9 – 15 wt.% of W. In the presence of CO32– the alloy composition is less dependent upon j and pH than in the absence of it. For better distribution of metal on the patterns, the pulse current deposition should be applied.