Direct copper electroless deposition on a tungsten barrier layer for ultralarge scale integration

In the present study, copper is deposited directly on tungsten using an electroless solution. Typically, Cu is deposited on a noble metal seed layer by an electroless process. The seed layers are platinum, palladium (Pd), silver, gold, rhodium, or iridium, while Pd is preferred. It has been proposed that copper (Cu) is deposited on tungsten (W) by a different mechanism. This work has implications for the direct plating of Cu/low k barrier layers. The best deposition conditions were found to be a CuSO4 concentration of 0.0305 mol/L, a solution PH of 11.8, and glyoxylic acid concentration of 0.09 mol/L at 60degreesC. Under the best conditions for 10 min, the grain shape is spherical, and the surface roughness is similar to11 nm. It is demonstrated that fine-grained, uniform copper film can be obtained for ultralarge scale integrated devices. The thickness of the film was 134 nm for 12 min. The deposition rate was 11.2 mm/min. According to increasing the PH, Cu film is of, the Cu2O phase and the grain shape of Cu is changed. Adjusting the PH resulted in oriented Cu and without impurity peaks during electroless deposition. The roughness of the Cu films depends greatly on the concentration of glyoxylic acid unlike PH changes. The resulting deposited copper concentration was 97 atom % as measured by Rotherford backscattering. The film of Cu/W has good adhesive strength, because a Cu/W alloy forms during electroless deposition. (C) 2005 The Electrochemical Society. All rights reserved.