 Solution

Start with a lightly boron-doped p-type Si wafer. Define an implantation opening for the pMOS region using an oxide/nitride implantation mask, then implant donor ions, commonly phosphorus, at energies and doses giving the required well depth and concentration. An anneal activates donors and repairs damage; thermal drive-in can deepen and smooth the well profile. The donor concentration must exceed the original acceptor concentration in the well. Retain p-type material outside it for the nMOS device. Form a later n+ well contact to tie the n-well to the positive supply; the p+ substrate contact ties the substrate to ground. Diffusion from a donor source is an alternative to ion implantation and drive-in.