Manufacturing approach for collector and a buried layer of bipolar transistor
This invention disclosed a manufacturing approach of collector and buried layer of a bipolar transistor. One aspect of the invention is that a pseudo buried layer, i.e, collector buried layer, is manufactured by ion implantation and thermal anneal. This pseudo buried layer has a small area, which makes deep trench isolation to divide pseudo buried layer unnecessary in subsequent process. Another aspect is, the doped area, i.e, collector, is formed by ion implantation instead of high cost epitaxy process. This invention simplified the manufacturing process, as a consequence, saved manufacturing cost.
1. A manufacturing process for a collector and a buried layer of a bipolar transistor comprises,
step 1: etching shallow trenches on a silicon substrate wherein depth of the trench is less than 2 μm;
step 2: doping bottoms of the shallow trenches with an impurity by ion implantation;
forming one or more doped regions in the silicon substrate near the bottom of the shallow trenches;
step 3: filling a dielectric into the shallow trenches to form a shallow trench isolation (STI);
step 4: annealing the silicon substrate with a predetermined temperature; linking the doped regions through lateral diffusion to form a pseudo buried layer,
step 5: implanting an active region between the STIs and above the pseudo buried layer by one or more ion implantations to convert the active region into the collector, wherein a doping concentration of the collector is lower than that of the pseudo buried layer.
2. The manufacturing process of claim 1 , wherein either a NPN bipolar transistor or a PNP bipolar transistor is formed;
wherein, if the NPN bipolar transistor is formed:
in step 1, the silicon substrate is p-type;
in step 2, the impurity is n-type and the doped regions are n-type;
in step 4, the pseudo buried layer is n-type and is doped;
in step 5, the one or more ion implantations are n-type and the collector is n-type;
wherein, if the PNP bipolar transistor is formed:
in step 1, the silicon substrate is n-type;
in step 2, the impurity is p-type and the doped regions are p-type;
in step 4, the pseudo buried layer is p-type and is doped;
in step 5, the one or more ion implantations are p-type and the collector is p-type.
3. The manufacturing process of claim 1 , wherein, in step 2, the ion implantation is carried out with a high ion dose and a low ion implant energy of less than 30 keV; wherein, if phosphorus, arsenic, antimony, titanium, or indium are implanted, the high ion dose is 1×10 14 ˜1×10 16 atoms per square centimeter, and if boron or boron fluoride is implanted, the high ion dose is 10 13 ˜1×10 16 atoms per square centimeter.
4. The manufacturing process of claim 1 wherein: in step 2, the ion implantation is carried out with a high dose of 1×10 13 ˜1×10 16 atoms per square centimeter and a high ion implant energy of more than 30 KeV and the ion implantation is performed to the silicon substrate between the STIs, and three doped regions are formed in silicon substrate; in step 4, the pseudo buried layer is formed by combining the three doped regions.