Bias electron cyclotron resonance (ECR) plasma deposition technology is proposed to planarize submicron interconnections with a high aspect ratio (height/space of interconnection) in which rf bias is applied to the substrate of the ECR plasma deposition system. The technology has the following advantages. First, the concave region of the narrow gap between submicron interconnections with a high aspect ratio above 1.0 can be planarized and formed at the same insulator thickness as that of the convex region. This is due to high directionality of ECR plasma particles. Second, both deposition and etching rates can be controlled by adjusting the gas flow rates as well as the rf and microwave power. Third, an rf bias can be applied from the initial stage of the planarization process. This is because of sputter‐etching with O2ions without Ar, thus enabling a shorter planarization time. Using the bias‐ECR plasma deposition technology, the 0.5 μm line/space Al (0.5 μm thickness) interconnection surface can be perfectly planarized.