3.6.2 P-well process

Prior to the n-well process p-well process was popular. P-well process is preferred in circumstances where balanced characteristics of the nMOS and pMOS are needed. It has been observed that the transistors in the native substrate tend to have better characteristics than that was made in a well. Because p devices inherently have lower gain than devices, n well process amplifies this difference while a p-well process moderates the difference. The standard p-well process steps are is similar to n-well process, except that a p-well is implanted instead of an n-well as a first step. Once the p-well is created, the active areas and subsequently poly gates can be defined. Later diffusions can be carried out to create source and drain regions. Finally, metal is deposited and patterned for contacts.