Semiconductor device and method of manufacturing thereof
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorTsuyoshi Koga
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Abstract
A LOCOS oxide film is provided in a main surface of a semiconductor substrate for isolating an element region from another element region. A channel cut layer formed of a P-type impurity is provided under the element region. A P.sup.+ impurity region having a concentration thicker than that of P-type impurity of channel cut layer is formed directly under a bird's beak portion of LOCOS oxide film in the main surface of semiconductor substrate. Therefore, an isolation breakdown voltage of an N-channel transistor region is increased.
Claims7
A semiconductor device, comprising:
- a semiconductor substrate having a main surface;
- a LOCOS oxide film provided in the main surface of said semiconductor substrate for surrounding an element region and isolating the element region from another element region;
- and
- an N-channel transistor provided in said element region,
- said LOCOS oxide film including a bird's beak portion,
- a channel cut layer having P-type impurity implanted therein being provided under said element region, and
- a P.sup.+ impurity region having a concentration greater than that of P-type impurity of said channel cut layer being formed only directly under said bird's beak portion of said LOCOS oxide film in the main surface of said semiconductor substrate.
A semiconductor device including an N-channel field transistor for forming an input protection circuit, comprising:
- a semiconductor substrate;
- a pair of N-type impurity regions formed spaced apart from each other in a main surface of said semiconductor substrate;
- a LOCOS oxide film having a bird's beak portion for surrounding and isolating said pair of N-type impurity regions;
- and
- a gate electrode provided on said LOCOS oxide film so as to bridge said pair of N-type impurity regions,
- a channel cut layer having P-type impurity implanted therein being further provided under said element region, and
- a P.sup.+ impurity region having a concentration greater than that of P-type impurity of said channel cut layer being formed only directly under said bird's beak portion of said LOCOS oxide film in the main surface of said semiconductor substrate.
A method of manufacturing a semiconductor device including an N-channel transistor and a P-channel transistor, comprising the steps of:
- forming a LOCOS oxide film including a bird's beak portion in a main surface of a semiconductor substrate;
- implanting first P-type impurity ions for channel doping into the main surface of said semiconductor substrate within an element region;
- implanting second P-type impurity ions into the main surface of said semiconductor substrate for forming a channel cut layer under said element region;
- forming said N-channel transistor on said semiconductor substrate within said element region;
- implanting third P-type impurity ions for forming P-type source/drain regions of said P-channel transistor at positions isolated from said element region in the main surface of said semiconductor substrate;
- implanting fourth P-type impurity ions for ROM determination into the main surface of said semiconductor substrate;
- and
- forming a P.sup.+ impurity region having a concentration greater than that of P-type impurity of said channel cut layer only directly under said bird's beak portion of said LOCOS oxide film.
Dependencies are inferred from the claim text.