Semiconductor device having buried bit line and method for fabricating the same

A method for fabricating a semiconductor device, comprising:

• forming an insulation layer over a semiconductor substrate;
• forming a metallic layer over the insulation layer;
• forming a plurality of buried metal bit lines and insulation layer patterns isolated by a plurality of trenches, wherein the plurality of trenches are formed by etching the metallic layer and the insulation layer;
• forming a sacrificial silicon layer by using selective epitaxial growth (SEG) to gap-fill the trenches;
• forming a seed layer doped with impurities on the entire surface of a structure including the sacrificial silicon layer by using solid phase epitaxy (SPE) after forming the sacrificial layer;
• forming an epitaxial silicon layer over the seed layer;
• and
• forming a plurality of pillars over each of the buried metal bit lines by etching the epitaxial silicon layer, the seed layer, and the sacrificial silicon layer, wherein each of the pillars comprises the seed layer and the epitaxial silicon layer,
• wherein the seed layer is in direct contact with the plurality of buried metal bit lines and the sacrificial layer,
• wherein the impurities are doped in situ.