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Method for Adjusting Gate Insulator Thickness of Selected Devices After Gate Definition

IP.com Disclosure Number: IPCOM000099950D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Kenny, DM: AUTHOR

Abstract

By causing "bird's beak" oxidation under gate conductors of selected devices, effective electrical dielectric thickness (Tox) may be increased under the gate of some devices to increase their switching threshold (Vt) levels. Thus, multiple on-chip power supply voltage levels may be accommodated and/or array and support circuits may be designed with devices having different Vt levels.

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Method for Adjusting Gate Insulator Thickness of Selected Devices After Gate Definition

       By causing "bird's beak" oxidation under gate conductors
of selected devices, effective electrical dielectric thickness (Tox)
may be increased under the gate of some devices to increase their
switching threshold (Vt) levels.  Thus, multiple on-chip power supply
voltage levels may be accommodated and/or array and support circuits
may be designed with devices having different Vt levels.

      Referring to the figure, normal processing results in thin gate
dielectric 2 on substrate 4 under gate electrode 6 which has
dielectric 8 formed on its sidewalls.  A thin layer of silicon
nitride (Si3N4) (not shown) is then conformally deposited and
selectively removed by photo masking and etching from devices
requiring increased Tox. High pressure oxidation at a temperature of
700 to 800 degrees Celsius is then used to form "bird's beak"
oxidation 10 extending under gate dielectric 2.

      Oxide growth 10 on gate conductor 6 may be avoided, if
required, by providing a cap nitride following gate conductor
deposition.

      Asymmetric growth of oxide 10 under only one side of gate
dielectric 2 can be accomplished by an appropriate change in the mask
used to define areas of Si3N4 to be etched off.