Semiconductor device and manufacturing method thereof

A semiconductor device comprising:

• a single crystalline semiconductor substrate of a first conductivity type;
• a first epitaxial semiconductor layer of a second conductivity type grown on the single crystalline semiconductor substrate;
• a second epitaxial semiconductor layer of the second conductivity type stacked on the first epitaxial semiconductor layer;
• a plurality of well regions of the first conductivity type formed in the second epitaxial semiconductor layer and separated from each other;
• an isolation layer of the first conductivity type formed between the well regions of the first conductivity type;
• a first buried layer of the first conductivity type abutting on a bottom of each of the well regions of the first conductivity type;
• a second buried layer of the second conductivity type abutting on a bottom of the first buried layer of the first conductivity type and electrically isolating each of the well regions of the first conductivity type from the single crystalline semiconductor substrate;
• and
• an MOS transistor formed in each of the well regions of the first conductivity type, wherein each of the well regions of the first conductivity type and a drain layer of the MOS transistor therein are electrically connected.

A manufacturing method of a semiconductor device comprising:

• providing a single crystalline semiconductor substrate of a first conductivity type;
• forming a first epitaxial semiconductor layer of a second conductivity type on the single crystalline semiconductor substrate;
• forming a second buried layer of the second conductivity type across a boundary between the single crystalline semiconductor substrate and the first epitaxaial semiconductor layer;
• forming a second epitaxial semiconductor layer of the second conductivity type on the first epitaxial semiconductor layer;
• forming a first buried layer of the first conductivity type across a boundary between the first epitaxial semiconductor layer and the second epitaxial semiconductor layer;
• forming a well region of the first conductivity type in the second epitaxial semiconductor layer, a bottom of the well region of the first conductivity type abutting on the first buried layer of the first conductivity type;
• and
• forming an MOS transistor in the well region of the first conductivity type.

A manufacturing method of a semiconductor device comprising:

• providing a single crystalline semiconductor substrate of a first conductivity type;
• introducing an impurity of a second conductivity type into a first region in the single crystalline semiconductor substrate;
• forming a first epitaxial semiconductor layer of the second conductivity type on the single crystalline semiconductor substrate;
• forming a second buried layer of the second conductivity type by diffusing the impurity of the second conductivity type;
• introducing a first impurity of the first conductivity type into a second region in the first epitaxial semiconductor layer above the second buried layer of the second conductivity type and an isolation region adjacent the second region
• forming a second epitaxial semiconductor layer of the second conductivity type on the first epitaxial semiconductor layer;
• forming a first buried layer of the first conductivity type and a lower isolation layer by diffusing the first impurity of the first conductivity type;
• introducing a second impurity of the first conductivity type into a third region in the second epitaxial semiconductor layer above the first buried layer of the first conductivity type;
• forming a well region of the first conductivity type abutting on the first buried layer of the first conductivity type by diffusing the second impurity of the first conductivity type;
• introducing a third impurity of the first conductivity type into a fourth region in the second epitaxial semiconductor layer above the lower isolation layer;
• forming an upper isolation layer overlapping with the lower isolation layer by diffusing the third impurity of the first conductivity type;
• and
• forming an MOS transistor in the well region of the first conductivity type.