The scaling of integrated-circuit device dimensions in the horizontal direction has caused an increase in aspect ratios of contact holes and vias without a corresponding scaledown in vertical dimensions. Conventional sputtering has become unreliable for handling higher aspect-ratio via/contact holes because of its poor step coverage. Several studies have attempted to overcome this problem by using W-CVD and reflow technology. The W-CVD is used for practical device fabrications. However, this technique has several problems such as poor adhesion to SiO2, poor W surface morphology, greater resistivity than Al, and the need of an etch-back process.Al reflow technology using a conventional DC magnetron sputtering system can simplify device-fabrication processes and achieve high reliability without Al/W interfaces. In particular, the Al reflow technology is profitable for multi-level interconnections in combination with a damascene process by using Al chemical mechanical polishing (CMP). These interconnections are necessary for miniaturized and high-speed devices because they provide lower resistivity than W and simplify fabrication processes, resulting in lower cost.This article describes recent Al reflow sputtering technologies as well as application of via and interconnect metallization.
