In order to realize minimum pitch interconnections without degrading reliability, self-aligned contacts (SACs) between interconnections and plugs are necessary. The planarized interconnections with SAC plugs is formed for quarter-micron size as follows. Interconnection trenches and contact holes are formed using a self-aligned etch-stop layer, followed by simultaneous metal-filling into the trenches and contact holes. Si-rich oxide (SRO) films are found to be promising for a self-aligned etch-stop layer with their high etching selectivity to SiO2 as high as 10-30. Sufficiently low line resistance of 15 k Omega /cm and low contact resistance of 70 Omega /contact are obtained with the quarter-micron W-interconnection with the SAC plugs.