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MOS Gate Insulator Patterning

IP.com Disclosure Number: IPCOM000112509D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Kitahara, H: AUTHOR [+3]

Abstract

Disclosed is a structure of MOS gate insulator that can reduce instability due to mobile ion in spite of the high temperature in CVD furnace. By depositing sputter silicon oxide under CVD gate insulator, mobile ion like sodium cannot move to across sputter silicon oxide. Then threshold voltage shift of MOS transistor with this process is smaller than the MOS transistor without this structure.

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MOS Gate Insulator Patterning

      Disclosed is a structure of MOS gate insulator that can reduce
instability due to mobile ion in spite of the high temperature in CVD
furnace.  By depositing sputter silicon oxide under CVD gate
insulator, mobile ion like sodium cannot move to across sputter
silicon oxide.  Then threshold voltage shift of MOS transistor with
this process is smaller than the MOS transistor without this
structure.

      As the temperature in CVD furnace is very high about
300ºC-450ºC, mobile ion like sodium is very easy to move.
Especially, MOS transistor on glass absorbs much amount of mobile ion
from glass due to the high temperature (Fig. 1).  With mobile ion in
gate insulator, as mobile ion creates instable charge in channel, the
characteristic of MOS transistor becomes also instable.  Though
silicon nitride is very famous to reduce mobile ion, the gas that is
used in gate metal etching process etches silicon nitride at high
etching rate, it is impossible to use it under gate metal as a
blocking layer of mobile ion (Fig. 2).  Depositing silicon nitride
over gate line, as silicon nitride contains much interface state,
charges are trapped in the film and threshold voltage shifts and
initial MOS transistor is not available in the long term.  Different
from CVD film, sputter silicon oxide has much smaller diffusion
length of mobile ion even in high temperature like 300-450C, so
sputter silicon oxide is adequate to block mobile ion from glass...