3. Gate Oxidation [Fig. 4.17(d)]. A thin thermal oxide is grown across the wafer. The portions of this oxide remaining after subsequent processing will provide the required gate oxide for the MOS transistors. Device performance is closely related to the growth of a dense, high-quality gate oxide.
4 Transistor Threshold Ion Implant [Fig. 4.17(d)] The boron implant adjusts the threshold voltage of p-channel and n-channel devices to the desired level. Thick field oxide prevents the boron from penetrating into the isolation regions.