Structure for picking up a collector and manufacturing method thereof

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.