Method for fabricating semiconductor device

A method for fabricating a semiconductor device, comprising:

• providing a substrate having a first lattice constant;
• and
• forming a first word line positioned in the substrate and a plurality of stress regions positioned adjacent to lower portions of sidewalls of the first word line;
• wherein the plurality of stress regions have a second lattice constant, the second lattice constant of the plurality of stress regions is different from the first lattice constant of the substrate;
• wherein forming a first word line positioned in the substrate and a plurality of stress regions positioned adjacent to lower portions of sidewalls of the first word line comprises:
• forming a first word line trench in the substrate;
• forming a coverage layer covered an upper portion of an inner surface of the first word line trench;
• forming a bottom mask layer on a bottom of the first word line trench;
• forming a plurality of side recesses extended outwardly at a lower portion of the inner surface of the first word line trench;
• forming the plurality of stress regions in the plurality of side recesses;
• removing the coverage layer and the bottom mask layer;
• forming a first word line insulating layer covered the inner surface of the first word line trench;
• forming a first word line electrode on the first word line insulating layer in the first word line trench;
• and
• forming a first word line capping layer on the first word line electrode in the first word line trench, wherein the first word line trench, the first word line insulating layer, the first word line electrode, and the first word line capping layer together form the first word line.