Implant

An implant is a process step that fires impurity atoms into silicon, drawn as a region that says where that dose is allowed.

The window covers part of the island and extends past it. The dose is allowed inside the window.

A transistor is not finished when poly and active are drawn. Threshold, the wells, and the source and drain flavor come from implants. The file shows a polygon on a sheet named nimp or pimp. The factory reads that sheet as a dose. A 0.4 micrometer implant enclosure around a contact is a typical rule. On screen the region is a hatched outline overlapping a transistor island, often drawn larger than the island so the dose still covers after alignment. Turn the sheet off and the device still looks drawn. It is not finished.

Implant is a process layer, not a metal film. It pairs with the well and with active. DRC checks those overlaps. LVS uses the same overlaps to decide nMOS versus pMOS. Screen color is a hint for n versus p. The layer pair and the map in the PDK are the truth.

Several implant layers can stack on one device: n-plus, p-plus, a threshold adjust, and a halo. The editor shows the outlines. The factory shows energies and doses. A rule can require n-plus to cover a source island and to stop before the shape crosses into a p-plus neighbor. Drawn as decoration after the devices look done, the implant can leave LVS passing while the threshold is wrong.

See what a layer is for, process layers vs drawing layers, and design rules and DRC.