Patent ID: 8865508

Claim:
A method of forming a semiconductor device having a backside illuminated image sensor, comprising: providing a first substrate and a second substrate; alternately forming multi-layered metal interconnections and multi-layered interlayer insulating layers on a first surface of the first substrate, wherein the metal interconnections have an uppermost metal interconnection on the interlayer insulating layers; forming a filling insulating layer filling spaces between sides of the uppermost metal interconnections on the interlayer insulating layers and covering upper surfaces of the uppermost metal interconnections; forming a buffer insulating layer softer than the filling insulating layer on the filling insulating layer; planarizing and wet-etching a surface of the buffer insulating layer; forming a capping insulating layer denser than the buffer insulating layer directly on the buffer insulating layer, wherein the filling insulating layer, the buffer insulating layer, and the capping insulating layer are formed of the same material; forming one or more alignment keys in the second substrate; bonding a surface of the capping insulating layer to a surface of the second substrate; forming color filters on a second surface of the first substrate; and forming microlenses on the color filters.