Patent ID: 8455975

Claim:
A parasitic PNP bipolar transistor in a silicon-germanium BiCMOS process, formed on a P-type silicon substrate, in which an active area is isolated by shallow trench field oxides, the PNP bipolar transistor comprising: a base region, composed of a first region and a second region, the first region being formed by a first N-type ion implantation region in the active area, the first region having a depth larger than that of the bottom of the shallow trench field oxides, a bottom part of the first region laterally extending into the bottom of the shallow trench field oxides on both sides of the active area, the second region being formed by a second N-type ion implantation region formed in an upper part of the first region, the second region having a doping concentration higher than that of the first region and a depth smaller than that of the bottom of the shallow trench field oxides; an N-type pseudo buried layer, formed by a third N-type ion implantation region formed at the bottom of the shallow trench field oxide on one side of the active area, the N-type pseudo buried layer being in contact with the first region, a base electrode being picked up through a deep hole contact formed on top of the N-type pseudo buried layer in the respective shallow trench field oxide; a collector region, formed by a P-type pseudo buried layer formed at the bottom of the shallow trench field oxide on the other side of the active area, the P-type pseudo buried layer being separated from the active area by a lateral distance, the P-type pseudo buried layer being in contact with the bottom part of the first region that laterally extends into the bottom of the shallow trench field oxides, a collector electrode being picked up through a deep hole contact formed on top of the P-type pseudo buried layer in the respective shallow trench field oxide, wherein by adjusting the lateral distance between the P-type pseudo buried layer and the active area, a bottom width of the bottom part of the first region can be adjusted, and hence a breakdown voltage of the parasitic PNP bipolar transistor can be adjusted; an emitter region, formed by a P-type silicon-germanium epitaxial layer formed on top of the active area and being in contact with the second region, an emitter electrode being picked up by a metal contact.