N-channel MOS transistors having source/drain regions with germanium

An n-channel MOSFET having source and drain regions improved with germanium, comprising:

• a semiconductor substrate having a surface;
• a thin dielectric layer on the surface of the semiconductor substrate;
• a patterned gate of conductive material on the thin dielectric layer, where the gate has opposite sides;
• and
• source and drain regions in the semiconductor substrate defining a channel in the semiconductor substrate between the source and drain regions, where the source and drain regions include a first n.sup.- region doped with phosphorus and aligned with the opposite sides of the gate and a second n.sup.30 region doped with arsenic and germanium, with the second n.sup.+ region overlapping the first n.sup.- region but spaced away from the sides of the gate.

An n-channel MOSFET having at least one source/drain region improved with germanium, comprising:

• a semiconductor substrate having a surface;
• a thin dielectric layer on the surface of the semiconductor substrate;
• a patterned gate of conductive material on the thin dielectric layer, where the gate has opposite sides;
• n.sup.- source/drain regions in the semiconductor substrate aligned to the opposite sides of and beneath the gate, defining a channel in the semiconductor substrate between the source/drain regions, where the n.sup.- source/drain regions are doped with phosphorus only;
• at least one sidewall spacer at the side of the gate;
• and
• an n.sup.+ source/drain region in the semiconductor substrate aligned to the sidewall spacer on the side of the gate, overlapping but not coextensive with one of the n.sup.- source/drain regions, where the n.sup.+ source/drain region is doped with germanium and an n-type dopant selected from the group consisting of phosphorus, arsenic and a combination thereof.