Method of manufacturing semiconductor element

A method of manufacturing a semiconductor element comprising:

• preparing a substrate having a silicon layer formed on an insulation film,
• forming a pad oxide film on the silicon layer,
• forming an oxide resistant film selectively on the pad oxide film so as to cover a portion of the pad oxide film and leave another portion exposed, the oxide resistant film having a peripheral region,
• forming a field oxide film by oxidizing the silicon layer under the portion of the pad oxide film exposed by the oxide resistant film, the formation of the field oxide film leaving a bird's beak region in the silicon layer beneath the peripheral region of the oxide resistant film,
• introducing an impurity of a first conductive type in the bird's beak region of the silicon layer under the field oxide film to form an impurity area,
• performing a heat treatment for the field oxide film after the impurity area is formed,
• removing the oxide resistant film and the pad oxide film from the heat treated substrate,
• forming a gate insulation film on the silicon layer,
• forming a gate electrode on the gate insulation film,
• forming a mask covering the field oxide film, and
• forming an impurity diffusion layer of a second conductive type in the silicon layer between the gate electrode and the field oxide film, wherein the impurity diffusion layer has an impurity density that is lower than that of the impurity area.

A method of manufacturing a semiconductor element comprising:

• preparing a substrate having a silicon layer formed on an insulation film,
• forming a pad oxide film on the silicon layer,
• forming an oxide resistant film selectively on the pad oxide film so as to cover a portion of the pad oxide film and leave another portion exposed, the oxide resistant film having a peripheral region,
• forming a field oxide film by oxidizing the silicon layer under the portion of the pad oxide film exposed by the oxide resistant film, the formation of the field oxide film leaving a bird's beak region in the silicon layer beneath the peripheral region of the oxide resistant film,
• introducing an impurity of a first conductive type in the bird's beak region of the silicon layer under the field oxide film to form an impurity area,
• forming a protection film to cover the area of the silicon layer under the field oxide film,
• performing a heat treatment for the field oxide film after the impurity area is formed,
• removing the oxide resistant film and the pad oxide film from the heat treated substrate,
• forming a gate insulation film on the silicon layer,
• forming a gate electrode on the gate insulation film, and
• forming an impurity diffusion layer of a second conductive type in the silicon layer between the gate electrode and the field oxide film, wherein the impurity diffusion layer has a density that is lower than that of the impurity area.