Method of making well regions for CMOS devices

Details Method of making well regions for CMOS devices Method of making well regions for CMOS devices

1982-04-08

1983-10-18

Ozaki, G.

Metal working

Method of mechanical manufacture

Assembling or joining

29576B, 29578, 148187, H01L 21265

Patent

active

044097263

ABSTRACT:
This invention significantly reduces the problem of undesired lateral diffusion of P type dopants into the P type active area. A thin oxide
itride sandwich is formed on the surface of a semiconductor wafer and patterned to serve as a mask defining the to-be-formed active areas. An N type dopant implant is performed on the surface of the wafer to establish the desired field inversion threshold voltage. The wafer is then oxidized, with the oxide
itride sandwich preventing oxide growth in the active areas. A layer of photoresist is applied to the wafer and patterned to expose the to-be-formed P well. That portion of the oxide exposed by the photoresist is removed, as is that portion of the substrate within the to-be-formed P well which contains N type dopants. P type impurities are then applied to the wafer. The photoresist is then removed and the P type dopants are diffused with little oxide growth to provide a P well having the desired dopant profile. Following this diffusion, a second, heavy concentration of P type dopant is implanted into the wafer at a sufficiently low energy to prevent the introduction of dopants into those portions of the wafer which are masked by the field oxide and the oxide
itride sandwich areas. The oxide
itride sandwich and the field oxide serve as masks, thus preventing the introduction of P type dopants in the field region or the active regions. Thus, the high concentration of P type dopants are introduced only in the periphery of the P well. The field oxide along the periphery of the P well is then regrown at a lower temperature than typically used for growing field oxide and diffusing dopants, thereby preventing substantial diffusion of the P type dopants. Thus, an active area within a P well is thereby formed wherein the width of the active area is not decreased due to P type dopant encroachment from the heavily doped periphery of the P well.

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