Semiconductor device and its manufacture

In a method of manufacturing a semiconductor device provided with a first bipolar transistor having a first conductivity type base region, a second bipolar transistor having a second conductivity type base region, a first conductivity type MOSFET, and a second conductivity type MOSFET on the same silicon substrate, the method of manufacturing the semiconductor device in which the formation of the impurity regions includes,

• a first ion implantation step of first conductivity type impurity for simultaneously forming a first conductivity type well region of the second conductivity type MOSFET and a first conductivity type annular isolation region making contact with the periphery of a collector formation region of the first bipolar transistor by means of an ion implantation of a first conductivity type impurity,
• a first ion implantation step of second conductivity type impurity for simultaneously forming a second conductivity type well region of the first conductivity type MOSFET and a second conductivity type insulation well region electrically isolating the second bipolar transistor and the first bipolar transistor by means of an ion implantation of a second conductivity type impurity,
• a second ion implantation step of first conductivity type impurity for forming a first conductivity type collector region of the second bipolar transistor by means of an ion implantation of a first conductivity type impurity,
• a second ion implantation step of second conductivity type impurity for forming a second conductivity type base region of the second bipolar transistor by means of an ion implantation of a second conductivity type impurity using the same mask as that used in the second ion implantation step of first conductivity type impurity,
• a third ion implantation step of first conductivity type impurity for forming a first conductivity type lower isolation region in a region including the collector formation region of the first bipolar transistor and a region further below by means of an ion implantation of a first conductivity type impurity,
• a third ion implantation step of second conductivity type impurity for forming a second conductivity type collector region in the collector formation region of the first bipolar transistor by means of an ion implantation of a second conductivity type impurity using the same mask as that used in the third ion implantation step of first conductivity type impurity, and
• a fourth ion implantation step of first conductivity type impurity for forming a first conductivity type base region of the first bipolar transistor by means of an ion implantation of a first conductivity type impurity using the same mask as that used in the third ion implantation step of second conductivity type impurity.