Semiconductor device and method of manufacturing thereof

A semiconductor device comprising:

• a semiconductor substrate of a first conductivity type;
• an epitaxial layer of a second conductivity type formed on the main surface of the semiconductor substrate;
• an isolation oxide film formed surrounding a first active region in the surface of the epitaxial layer;
• a first MOS type field effect transistor having a channel region of a first conductivity type and formed on said first active region;
• a second MOS type field effect transistor having a channel region of a second conductivity type, and a bipolar transistor both formed on a second active region sandwiching the first MOS type field effect transistor and said isolation oxide film so as to be adjacent to one another, wherein
• said first active region includes
• a well of a first conductivity type formed having a predetermined depth from the surface of said epitaxial layer,
• a channel stop layer of a first conductivity type formed having the peripheral top portion contacting the bottom face of said isolation oxide film, surrounding the bottom face of said well of a first conductivity type, and having the bottom face of said channel stop layer of a first conductivity type positioned higher than the main surface of said semiconductor substrate, and
• a buried layer of a first conductivity type buried having the top face contacting the bottom face of said channel stop layer of a first conductivity type and the bottom face of said buried layer of a first conductivity type positioned lower than the main surface of said semiconductor substrate,
• wherein the well has a peak impurity concentration located at a depth below its top face and above its bottom face, the channel stop layer has a peak impurity concentration located at a depth below its top face and above its bottom face, and the buried layer has a peak impurity concentration located at a depth below its top face and above its bottom face, and
• further wherein the bottom face of the well and the top face of the channel stop layer are located where a decrease in the impurity concentration from the maximum in the well ends and an increase in the impurity concentration toward the maximum in the channel stop layer begins, and the bottom face of the channel stop layer and the top face of the buried layer are located where a decrease in the impurity concentration from the maximum in the channel stop layer ends and an increase in the impurity concentration toward the maximum in the buried layer begins.