Method for forming a strained channel in a semiconductor device

A method for forming a strained channel in a semiconductor device is provided, comprises providing of a transistor comprising a gate stack exposed with a gate electrode on a semiconductor substrate, a pair of source/drain regions in the substrate on opposite sides of the gate stack and a pair of spacers on opposing sidewalls of the gate stack. A passivation layer is formed to cover the gate electrode and spacers of the transistor. A passivation layer is formed to cover the gate electrode and the spacers. A recess region is formed in each of the source/drain regions, wherein an edge of the recess region aligns to an outer edge of the spacers. The recess regions are filled with a strain-exerting material, thereby forming a strained channel region in the semiconductor substrate between the source/drain regions.