Semiconductor device having contact plug formed in double structure by using epitaxial stack and metal layer and method for fabricating the same

A method for fabricating a semiconductor device comprising the steps of:

• forming a plurality of gate patterns directly on a substrate;
• filling the space between the gate patterns by forming an inter-layer insulation layer on the substrate;
• forming a contact hole, which exposes a predetermined surface of the substrate between the gate patterns, by selectively etching the inter-layer insulation layer;
• performing a first pre-cleaning process to recover a defect on a bottom portion of the contact hole and remove a first natural oxide layer;
• forming a sacrificial layer at a temperature, where an amorphous structure is formed, to remove a fine oxide layer remaining on a surface of the substrate of the bottom portion of the contact hole after performing the first pre-cleaning process;
• removing the sacrificial layer;
• forming an epitaxial stack including at least a SEG-silicon germanium layer through the SEG process on the contact hole;
• performing a second pre-cleaning process to remove a second natural oxide layer on a surface of the epitaxial stack;
• and
• forming a metal layer filling the contact hole on the epitaxial stack,
• wherein a surface of the metal layer is formed on a same plane as a surface of the gate patterns.