Electroplating of nickel-tungsten barrier layers

The properties of electrodeposited Ni/W alloys are discussed. Alloys ranging in W content from zero up to 50 a/o have been prepared and their crystal structures were determined. Amorphous alloys are consistently obtained in the range of 20 - 40 a/o of W. These alloys are good potential candidates for barrier-layer film formation in ULSI devices, separating the silicon substrate from the copper. The complex nature of the solution chemistry that plays a crucial role in the formation of the alloy is discussed. High W content in the alloy is obtained if ammonia is eliminated from the solution. Hydrogen evolution is observed as a side reaction. The W content of the alloy drops sharply as the pH is changed from 8 to 9. Local increase in pH may occur in restricted areas, having high-aspect-ratios.