Organic Solution Deposition of Copper Seed Layers onto Barrier Metals
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Organic Solution Deposition of Copper Seed Layers onto Barrier Metals H. Gu, R. Fang, T. J. O'Keefe, M. J. O’Keefe, W.-S. Shih1, J. A. M. Snook1, K. D. Leedy2 and R. Cortez2 University of Missouri-Rolla, Dept. of Metallurgical Engineering and Materials Research Center, Rolla, MO 65409, U.S.A. 1 Brewer Science, Inc., Rolla, MO 65401, U.S.A. 2 Air Force Research Laboratory, Sensors Directorate, Wright-Patterson AFB, OH 45433, U.S.A ABSTRACT Spontaneous deposition of copper seed layers from metal bearing organic based solutions onto sputter deposited titanium, titanium nitride, and tantalum diffusion barrier thin films has been demonstrated. Based on electrochemically driven cementation exchange reactions, the process was used to produce adherent, selectively deposited copper metal particulate films on blanket and patterned barrier metal thin films on silicon substrates. The organic solution deposited copper films were capable of acting as seed layers for subsequent electrolytic and electroless copper deposition processes using standard plating baths. Electroless and electrolytic copper films from 0.1µm to 1.0µm thick were produced on a variety of samples on which the organic solution copper acted as the initial catalytic seed layer. The feasibility of using organic solution deposited palladium as a seed layer followed by electroless copper deposition has also been demonstrated. In addition, experiments conducted on patterned barrier metal samples with exposed areas of dielectric such as polyimide indicated that no organic solution copper or palladium deposition occurred on the insulating materials. INTRODUCTION The incorporation of low-k dielectrics and copper interconnects in the fabrication of high speed silicon integrated circuits (ICs) requires significant changes to the current method of using blanket deposition and etch back processes. While physical vapor deposition (PVD) techniques, such as sputtering, appear to be viable for the formation of thin barrier layers between the low-k dielectric and copper interconnect, technical and economic benefits of using chemical vapor deposition (CVD) [1], electrolytic plating [2], and electroless plating [3] processes for build up of the copper interconnects make these approaches attractive alternatives. Electrochemical deposition of copper is relatively inexpensive compared to vapor deposition methods but suffers from the fact that the barrier layers, typically titanium or tantalum based metals or metal nitrides, are difficult to electrochemically activate and plate with adherent copper. In fact, in the primary electrolytic copper metals industry, titanium is employed as a re-usable cathode material because the copper is easily removed from the titanium surface after plating. Therefore, it is necessary to deposit adherent, thin seed layers of copper onto the barrier layer prior to deposition of thicker copper films by electrochemical methods. Although PVD and CVD copper seed layers can be used to fabricate electroplated copper interconnects, an electrochemical process for d
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