Patent ID: 8710587

Claim:
A method of manufacturing an LOMOS device which has a source and a drain arranged to be separated from each other on both sides of a substrate with a gate interposed there between, the method comprising: implanting first conduction type impurity ions into the first regions of the substrate forming first conduction type impurity regions in the substrate, wherein a second region of the substrate remains undoped and the undoped second region includes a first portion on which the source is to be formed and at least one second portion positioned between the first portion and a on which the drain is to be formed; forming an oxide film on the first regions of the substrate through an oxidation process; performing an impurity implantation process with the oxide film as an ion implantation mask to implant second conduction type impurity ions into the second region forming a second conduction type impurity region at the first portion and at least one second conduction type impurity ring at the at least one second portion; removing the oxide film and performing a thermal process on the semiconductor substrate, forming i) a first conduction type deep well serving as a drift region of the LOMOS device from the first conduction type impurity region in the substrate, ii) a second conduction type well connected to the drift region from the a second conduction type impurity region at the first portion, and iii) at least one internal field ring in the drift region from the at least one second conduction type impurity ring at the at least one second portion; and then forming a field oxide film on the substrate above the at least one internal field ring.