Ultra-flat and ultra-smooth Cu surfaces produced by abrasive-free chemical–mechanical planarization/polishing using vacuum ultraviolet light

The new bonding technologies utilizing intermolecular bonding forces have been developed and attracting attention recently. Cu is known to be a suitable material for the bonding substrate due to its excellent physical properties. And an ultra flatness and an ultra smoothness over a relatively large area are strongly required for the Cu substrate surface.Chemical–mechanical planarization/polishing (CMP) with abrasives is widely adopted for planarizing and smoothing Cu surfaces. But this method has serious problems resulting from abrasives in CMP slurry. Hence, we have developed an abrasive-free polishing (AFP) method that utilizes vacuum ultraviolet (VUV) light in the previous study and an ultra-smooth Cu surface was achieved. However, the problems about a low removal rate and a small finished area remained.To overcome the problem, a new manufacturing process, namely, the process of combining CMP with abrasives and the AFP method was newly developed. First, an ultra-flat surface is achieved using CMP with abrasives. Next, the AFP method is applied for the final polishing step in order to achieve an ultra-smooth surface. As a result, utilizing VUV in situ irradiation and electrolyzed reduced water in the AFP process, the ultra-flat and the ultra-smooth surface produced has a roughness average of <1 nm with a peak value of <10 nm over a relatively large area of 700 μm × 500 μm.