Vertical semiconductor device and method for fabricating the same

A method for fabricating a semiconductor device, comprising:

• forming a first multi-layer stack including liner layers and a source sacrificial layer over a lower structure;
• forming a second multi-layer stack including dielectric layers and sacrificial layers over the first multi-layer stack;
• forming a vertical contact recess extending through the second multi-layer stack and the source sacrificial layer;
• replacing the source sacrificial layer with a source contact layer;
• replacing the sacrificial layers with conductive layers;
• forming a seed layer on a sidewall of the vertical contact recess to seal the conductive layers;
• forming a carbon-containing spacer on the seed layer;
• and
• forming a source contact plug in the vertical contact recess.