Semiconductor device having MOS transistors and bipolar transistors on a single semiconductor substrate

摘要

The invention is directed to reducing of the number of steps in a BiCMOS process. A first N-well 3 A and a second N-well 3 B are formed deeply on a surface of a P-type semiconductor substrate. A first P-well 4 A is formed in the first N-well 3 A, and an N-channel MOS transistor is formed in the first P-well 4 A. The second N-well 3 B is used as a collector of a vertical NPN bipolar transistor. A second P-well 4 B is formed in the second N-well 3 B. The second P-well 4 B is formed simultaneously with the first P-well 4 A. The second P-well 4 B is used as a base of the vertical NPN bipolar transistor. An N+ emitter layer and a P+ base electrode layer of the vertical NPN bipolar transistor are formed on a surface of the second P-well 4 B.