Uniform junction formation in FinFETs

A method comprising:

• forming a fin on a semiconductor substrate;
• forming a first gate structure on the fin, the first gate structure comprising a first gate in contact with a side surface and a top surface of the fin and a first spacer surrounding the first gate;
• forming a second gate structure on the fin, the second gate structure comprising a second gate in contact with the side surface and the top surface of the fin and a second spacer surrounding the gate;
• removing part of the fin between the first gate and the second gate to form a fin recess, the fin recess having a first sidewall that is substantially flush with a sidewall of the first gate and second sidewall that is substantially flush with a sidewall of the second gate, wherein a portion of the fin remains below the fin recess;
• forming a buffer layer on the first sidewall, the second sidewall, and a bottom surface of the fin recess, the buffer layer having a first facet below the first spacer and a second facet below the second spacer;
• forming a doped epitaxial S-D region on the buffer layer in the fin recess;
• annealing the doped epitaxial S-D region to diffuse dopant atoms into a region of the fin below the first gate and the second gate to form an abrupt junction;
• wherein the forming the doped epitaxial S-D region on the buffer layer in the fin recess comprises:
• growing an epitaxial material on the buffer layer in one or more layers;
• doping the epitaxial material with dopant atoms such that the epitaxial material is highest doped at the bottom with decreasing dopant concentration toward a top of the doped epitaxial S-D region;
• and
• wherein the abrupt junction profile comprises a first facet and a second facet directly below the gate.