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Mosfet with Localized Channel and Punch-Through Implants to Reduce Source/Drain Junction Capacitance

IP.com Disclosure Number: IPCOM000114001D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 169K

Publishing Venue

IBM

Related People

Bindal, A: AUTHOR

Abstract

A MOSFET structure with localized channel implant is discussed. The intent behind this structure is to reduce the Source/Drain (S/D) junction capacitance to a minimum value so that the delay of the circuits containing such transistors can be improved with respect to the ones with conventional transistors.

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Mosfet with Localized Channel and Punch-Through Implants to Reduce
Source/Drain Junction Capacitance

      A MOSFET structure with localized channel implant is discussed.
The intent behind this structure is to reduce the Source/Drain (S/D)
junction capacitance to a minimum value so that the delay of the
circuits containing such transistors can be improved with respect to
the ones with conventional transistors.

      To manufacture transistors which provide high circuit speeds
has been the driving force of semiconductor industry for decades.
Shorter MOSFET channel lengths and smaller source/drain contact areas
have been the main target areas to increase transistor
transconductance and to achieve high circuit speeds.  However, short
MOSFET channel lengths usually need higher channel doping density to
prevent punch-through between the source and drain junctions for a
given drain bias.  Since the implant to provide such a channel doping
is unmasked over the entire device area, when a 1e20 cm-3 range
source/drain junction interfaces with this high channel doping, it
creates a large junction capacitance which, in turn, defeats the
purpose of using short channel length devices to minimize gate
delays.  Therefore, to solve this fundamental problem another MOSFET
structure is proposed which practically eliminates this high
source/drain junction capacitance.

      The cross section of the proposed device is shown in Fig. 1.
In this structure, the channel implant is localized only under the
channel to provide enough threshold and punch-through resistance, but
not under the source/drain junctions.  Therefore, both source and
drain junctions interface with the substrate (or n-well for pMO...