Electroplating of Amorphous Thin Films of Tungsten/Nickel Alloys

Abstract

The electroplating of amorphous Ni/W alloys is described. The aqueous plating solution consists of NiSO4, Na2WO4, and Na3Cit at pH = 8.0. The bath is operated at room temperature. By avoiding the use of NH4OH or any ammonium salt, it was possible to prepare alloys containing up to 50 a/o (76 w/o) W. XRD measurements revealed that amorphous alloys were obtained when the concentration of W in the alloy is 20−40 a/o. At lower concentrations of W the fcc substitutional solid solution Ni(1-x)Wx was formed. At higher concentration, an orthorhombic crystal structure corresponding to a 1/1 Ni/W alloy was observed. SEM and STM measurements supported the existence of the amorphous phase. The conditions under which amorphous alloys are expected to be formed preferentially are discussed. Thin films of the amorphous phase were prepared reproducibly at any tungsten concentration in the above range. Therefore, these alloys can be used for barrier or capping layers in the microelectronic industry for ULSI and MEMS applications.