Methods for fabricating a stressed MOS device is provided. One method
comprises the steps of providing a monocrystalline semiconductor
substrate having a surface and a channel abutting the surface. A gate
electrode having a first edge and a second edge is formed overlying the
monocrystalline semiconductor substrate. The substrate is anisotropically
etched to form a first recess aligned with the first edge and a second
recess aligned with the second edge. The substrate is further
isotropically etched to form a third recess in the substrate extending
beneath the channel. The third recess is filled with an expanding
material to exert an upward force on the channel and the first and second
recesses are filled with a contact material. Conductivity determining
ions are implanted into the contact material to form a source region and
a drain region aligned with the first and second edges, respectively.