Method of manufacture of pull down transistor with drain off-set for low leakage SRAM's
AssigneeUnited Microelectronics Corp.
InventorMing-Tzong Yang
Life of this patent
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Abstract
The pull down transistor of a static SRAM semiconductor device is formed with oxide and polysilicon regions formed on a doped silicon substrate. A masking area is formed over the drain side of the polysilicon and the areas of the drain region proximal to the gate structure in the silicon and oxide layers below. N+ dopant is implanted into the unmasked areas of said substrate about the polysilicon region with the drain doping offset by the resist overlying the proximal portion of the drain region. A spacer is formed by chemical vapor deposition about the polysilicon region. Next an N- implantation follows with the offset provided by the spacers about the polysilicon region.
Claims10
A process of forming an asymmetric pull-down transistor within an SRAM, the process comprising
- a) forming a polysilicon gate structure on a semiconductor substrate of a first conductivity type;
- b) forming a mask in an area on the drain side of said polysilicon gate structure, leaving the remainder of said gate structure as well as a portion of said substrate unmasked,
- c) implanting a first N-type dopant into the unmasked areas of said substrate to form source and drain regions with an N+ doped region of said drain offset away from said gate structure by said mask and with an N+ doped region of said source aligned to the edge of said gate structure,
- d) forming insulating spacers proximate said gate structure,
- e) implanting a second dopant into the outer portion of said source region beyond said spacer and below said source region beyond said spacer and into and extending below said N+ doped region of said drain and between said N+ doped region of said drain and said spacer proximate thereto said second dopant being an N- dopant, thereby forming a pull down transistor coupled to other devices within an SRAM,
- whereby said SRAM is a low leakage SRAM device.
Dependencies are inferred from the claim text.