FreeLists / si-list / [SI-LIST] Re: Fwd: vgs stress in digital cmos process

[Christopher Jakubiec <Christopher.Jakubiec@xxxxxxx>]

Hi,

High voltage on either the gate (Vgs) or the drain (Vds) can cause reliabil=
ity=20
problems in the 0.18um CMOS process.  There are two seperate physical issue=
s=20
taking place here though.  Raising the voltage on the gate (Vgs) increases =
the=20
electric field across the gate-oxide-channel/bulk.  So, the stress in this =
case=20
is on the gate oxide layer, and the extent of the stress depends on the oxi=
de=20
thickness.  Thinner oxides will be experience more stress for a given gate=
=20
voltage.  An over-stressed oxide can rupture, cause significant leakage, an=
d=20
ultimatley lose gate control.  On the drain node, raising the voltage (Vds)=
 can=20
generate high electric fields near the drain.  The effect of high electric=
=20
fields near the drain is hot carrier injection into either or both the gate=
=20
oxide and the substrate.  This can cause significant substrate current, and=
 can=20
also effect the threshold voltage of the transistor.  If the channel length=
 is=20
short, this can also open up a series of short channel effects.  Generally=
=20
people are more interested in how high they can drive the drain voltage to=
=20
obtain maximum speed/drive current, and thus reliablilty concerns are focus=
ed=20
there.  Be aware if you are using thin gate oxides with higher than nominal=
=20
voltages on the gate, this can be problematic as well.

Chris Jakubiec
Product Engineer
Sun Microsystems


>=20
> HI, experts:
> =20
> I want to know that in 0.18um Digital CMOS process, major stress concern =
is=20
Vgs or Vds?
> =20
> i.e., if 1.8v NMOS's Vgs is higher than 1.8v, such as 1.9 or 2.2, will th=
at=20
cause reliability problem?
> =20
> According to one paper, only Vds higher than 1.8v will cause reliability=
=20
issue. The margin for Vgs will be much higher.
> =20
> Can any people familiar with silicon explain it for me? TSMC data may be =
used=20
for reference.
> =20
> Thanks!
> =20
> BH
> (If you have received , please ignore, thanks)
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