Method of doing ESD protective device ion implant without additional photo mask

摘要

A method of forming ESD protective transistor is disclosed, which is performed by ion implant into the drain contact hole of the ESD protective transistor, wherein the contact hole are fabricated simultaneously with the gate contact holes of the functional transistor and of the ESD protective transistor. Both of the transistors have a respective metal silicide layer cap the polysilicon layer to prevent depleted region formed in the poly-gate for ion implant using p type ions. The p type ions are to increase the instant current tolerance. Alternatively, the ion implant is using n type ions to increase the punchthrough ability of the ESD protective transistor. In the latter case, the metal silicide layer in the gate regions of both transistors is optional.