SCMOS Layer Guide

The "active" layer determines the source-gate-drain locations of both NMOS and PMOS devices. The opposite of active determines where the field oxide is grown. The overlap of the active layer and the poly layer determines where the gate oxide is grown.

The "P-select" layer covers the PMOS device with photoresist so that the NMOS can be ion implanted with n-type ions to form the doped source and drain.

The "N-select" layer covers the NMOS device with photoresist so that the PMOS can be ion implanted with p-type ions to form the doped source and drain.

Some processes (i.e. not MOSIS) do not have the select layers and instead have separate n and p active layers. The select layer is then derived from this. (This means there are only 2 instead of 3 drawn layers in these processes.)

Also note that the video today showed an additional implant from what we described in class. The implant was before the source and drain implant and before poly. It is the threshold implant which adjusts the characteristics of the transistor. We will discuss this more on monday when I get into the electrical characteristics of MOS devices.