An acid-based electroless Cu deposition process: Chemical formulation, film characteristics and CMP performance

Abstract

In this contribution, we report the chemical process of, and material properties derived from an acid-based electroless Cu deposition system employing CuCl2-HNO3 in a HFNH4F buffer solution. With the help of nitric acid, Cu can be deposited on Si/Ta/TaN substrate without the insertion of a Cu seed layer. The deposition rate is found to decrease with increasing [HNO3] in the solution and is sensitive to variation in [Cl-] concentration. Overall, a deposition rate of 2700 Å/min with a as-deposited Cu resistivity of 2.35 μΩcm can be achieved, which can be reduced to 2.13 μΩ-cm upon annealing. The chemical-mechanical polishing (CMP) rates of these electroless Cu films increases with the grain size in the as-deposited Cu film but decreases with the grain size after annealing.