Investigation of copper agglomeration at elevated temperatures

In this work, the agglomeration behavior of copper thin films after high temperature annealing was investigated. Cu (200 or 50 nm)/Ta (10 nm, or no Ta)/TaN (50 nm)/Ta (10 nm) layers were deposited onto SiO2 (270 nm)/Si substrates by magnetron sputtering. All samples were annealed in vacuum at temperatures ranging from 400 to 800degreesC. The sheet resistance, phases, surface morphology, elemental depth profiles, and chemical binding states were investigated by four-point probe, theta-2theta X-ray diffraction, scanning electron microscopy (SEM), Auger electron spectroscopy, and X-ray photoelectron spectroscopy (XPS). Experimental results revealed that 50 nm thick copper films deposited directly onto TaN agglomerated after annealing at 600degreesC. No copper agglomeration was observed for 200 nm thick copper films even after annealing at 800degreesC. It is also observed that copper agglomeration was prevented while a Ta layer was interposed between Cu and TaN. SEM and XPS results showed that, with a Ta interposed interlayer, copper grain growth was slowed down and Ta out-diffused to the copper surface to form a TaOx layer. The slow grain growth rate of copper and forming of TaOx cap layer are believed to be the main reasons for preventing copper agglomeration. (C) 2003 The Electrochemical Society.