US Patent 10991628 Etch stop layer between substrate and isolation structure

A device includes a substrate; semiconductor fins extending from the substrate; an isolation structure over the substrate and laterally between the semiconductor fins; a liner layer between sidewalls of the semiconductor fins and the isolation structure; and an etch stop layer between the substrate and the isolation structure and laterally between the semiconductor fins. The etch stop layer includes a material different than that of the isolation structure and the liner layer.