Pulse electrodeposition of Ni-W alloy for trench filling in microelectromechanical systems.

The effect of pulse current (PC) on Ni-W alloy electrodeposition was investigated to fill the trenches with aspect ratio 1:2 for MEMS applications. Rapid deposition of top side in trench produced a void in electrodeposits with direct current (DC). Morphology of Ni-W electrodeposition inside trench was strongly influenced by the applied current density and the current off-time (t(off)). Enhanced filling phenomena were observed with increasing current off-time because of decreasing concentration gradient between top and bottom in trench. The complete Ni-W filling of trench was achieved with a current density of 200 mA/cm2 and a current on- and off-time of 100 ms and 300 ms, respectively. Amorphous structure was revealed in both DC and PC electrodeposits and the concentration of W in Ni-W electrodeposits for complete filling of trench was about 24% in atomic ratio.