To start CHMOS de-vice production 150 mm (6"), high-resistivity, (100) orientation, single crystal p type
(boron doped) silicon wafers are used. P-type silicon is required to create n-channel transistors To create p-channel transistors, necessary for CHMOS devices n-type (ar- senic or phosphorous doped) silicon regions (n-wells) are implanted. The wafer is masked, then implanted to create p-type and n-type silicon regions on the same wafer. The n-well provides the background doping for the p-channel transistors while the p- type, start material (protected from the implant by the unexposed photoresist) serves as the background doping for n-channel transistors. A high temperature drive cycle completes the formation of the well by thermal dopant transition.