Patent ID: 8803279

Claim:
A structure for picking up a collector region, the collector region being formed in a substrate and sandwiched between two isolation regions, the structure comprising: a pair of polysilicon stacks formed in the isolation regions and extending below the collector region; and a pair of collector electrodes contacting on the polysilicon stacks, wherein the pair of polysilicon stacks comprising: a first polysilicon layer located below the isolation regions, the first polysilicon layer having a first side face contacting with the collector region, an angle between the first side face and a bottom surface of the first polysilicon layer being smaller than 90 degrees; and a second polysilicon layer located on and in contact with the first polysilicon layer, wherein both the first and second polysilicon layers have an opposite conductivity type to a conductivity type of the substrate, wherein the first polysilicon layer is doped with a dopant having either a higher diffusivity or a higher concentration than a dopant of the second polysilicon layer, and wherein a depth of the polysilicon stacks is greater than a depth of the collector region; the depth of the collector region is greater than a depth of the second polysilicon layer; and the depth of the second polysilicon layer is greater than a depth of the isolation regions.