Metal working – Method of mechanical manufacture – Assembling or joining
Patent
1985-06-28
1987-06-23
Roy, Upendra
Metal working
Method of mechanical manufacture
Assembling or joining
29576W, 29578, 148 15, 148175, 357 34, H01L 2131, H01L 2176
Patent
active
046741739
ABSTRACT:
One embodiment of the present invention provides a method whereby a symmetrical transistor may be fabricated which eliminates the problems of scalability caused by the requirement of fabricating an extrinsic base. The method accomplishes this by the use of a polysilicon extrinsic base structure which is formed in a trench containing an insulating layer in the bottom of the trench formed by differential oxidation.
After fabricating appropriate isolation structures, two trenches for either side of the intrinsic base are cut into the surface of the substrate. The bottom of these trenches are then heavily doped. A silicon dioxide layer is then thermally grown in the trenches. Because the bottoms of the trenches are heavily doped, a thicker silicon dioxide layer is formed in the bottom of the trenches. This silicon dioxide layer is then etched so that the silicon dioxide layer is completely removed from the sides of the trench but remains in the bottoms of the trench. The trenches are then filled with polycrystalline silicon. After the fabrication of the intrinsic base, the emitter and the contact to a subcollector, dopant ions are implanted into the polycrystalline silicon extrinsic base thereby heavily doping the extrinsic base. This implantation is driven in which causes a P+ region to be formed on the edges of the intrinsic base thus providing good contact between polycrystalline silicon extrinsic base and the intrinsic base. Because this implantation is performed as one of the last steps in fabricating the transistor, the undesirable effects of out diffusion of the extrinsic base are eliminated.
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Malaviya, S. D., IBM-TDB, 24 (1982), 5578.
Hahn Larry A.
Havemann Robert H.
Hill Kenneth C.
Roy Upendra
Sharp Melvin
Sorensen Douglas A.
Texas Instruments Incorporated
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