Parasitic PNP bipolar transistor in a silicon-germanium BiCMOS process
View Patent ↗A parasitic PNP bipolar transistor, wherein a base region includes a first and a second region; the first region is formed in an active area, has a depth larger than shallow trench field oxides, and has its bottom laterally extended into the bottom of the shallow trench field oxides on both sides of an active area; the second region is formed in an upper part of the first region and has a higher doping concentration; an N-type and a P-type pseudo buried layer is respectively formed at the bottom of the shallow trench field oxides; a deep hole contact is formed on top of the N-type pseudo buried layer to pick up the base; the P-type pseudo buried layer forms a collector region separated from the active area by a lateral distance; an emitter region is formed by a P-type SiGe epitaxial layer formed on top of the active area.
1. 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.
2. The parasitic PNP bipolar transistor in a silicon-germanium BiCMOS process according to claim 1 , wherein process conditions of the first N-type ion implantation of the first region are as follows: implantation dose is 1e12 cm −2 to 5e14 cm −2 ; implantation energy is 50 KeV to 500 KeV; implantation window has a width larger than that of the active area.
3. The parasitic PNP bipolar transistor in a silicon-germanium BiCMOS process according to claim 1 , wherein process conditions of the second N-type ion implantation of the second region are as follows: single implantation or multiple implantations; total implantation dose is 5e12 cm −2 to 1e14 cm −2 ; implantation energy is 10 KeV to 100 KeV; implantation window has a width smaller than or equal to that of the active area.
4. The parasitic PNP bipolar transistor in a silicon-germanium BiCMOS process according to claim 1 , wherein the N-type pseudo buried layer is formed by a third N-type ion implantation conducted before forming the shallow trench field oxides, and the process conditions of the third N-type ion implantation are as follows: impurity implanted is arsenic or phosphorous; implantation dose is larger than 5e14 cm −2 ; implantation energy is 1 KeV to 100 KeV.
5. The parasitic PNP bipolar transistor in a silicon-germanium BiCMOS process according to claim 1 , wherein the P-type pseudo buried layer of the collector region is formed by a P-type ion implantation conducted before forming the shallow trench field oxides, and the process conditions of the P-type ion implantation are as follows: impurity implanted is boron or boron difluoride; implantation dose is 1e13 cm −2 to 1e16 cm −2 ; implantation energy is 1 KeV to 100 KeV.
6. The parasitic PNP bipolar transistor in a silicon-germanium BiCMOS process according to claim 1 , wherein the P-type silicon-germanium epitaxial layer is doped by an ion implantation process with conditions as follows: implantation dose is larger than 1e15 cm −2 ; impurity implanted is boron or boron difluoride; implantation energy is configured such that the impurities implanted can go through the P-type silicon-germanium epitaxial layer and enter into the active area below the P-type silicon-germanium epitaxial layer by a depth of 100 Å to 500 Å.
7. The parasitic PNP bipolar transistor in a silicon-germanium BiCMOS process according to claim 1 , wherein the deep hole contact is formed by opening a deep hole in the shallow trench field oxide, depositing a titanium/titanium nitride barrier metal layer in the deep hole, and filling tungsten into the deep hole.