A method of forming a retrograde well in a transistor is provided. A
transistor structure having a substrate, a gate, and a gate oxide layer
between the substrate and the gate is formed. The substrate includes a
channel region located generally below the gate. A first dopant is
implanted into the channel region. A second dopant is implanted into the
substrate to form a doped source region and a doped drain region. A third
dopant is implanted into the gate oxide layer. A source/drain anneal is
performed to form a source and a drain in the doped source region and the
doped drain region, respectively. The source/drain anneal causes a
portion of the first dopant in the channel region to be attracted by the
third dopant into the gate oxide layer.