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Number 2535
Application Note Monitoring Channel Hot Carrier (CHC)
Series Degradation of MOSFET Devices using
Keithley Model 4200-SCS
Introduction Pre-Stress
characterization
Channel Hot Carrier (CHC) induced degradation is an important
reliability concern in modern ULSI circuits. Charge carriers gain Fail?
Yes
Stop
kinetic energy as they are accelerated by the large electric field No
across the channel of a MOSFET. While most carriers reach the Record data
drain, hot carriers (those with very high kinetic energy) can gen-
erate electron-hole pairs near the drain due to impact ionization Stress
Yes
from atomic-level collisions. Others can be injected into the gate
Fail?
channel interface, breaking Si-H bonds and increasing interface
Increase stress time No
trap density. The effect of CHC is time dependant degradation of
Interim test
device parameters, such as V T, IDLIN, and IDSAT.
This channel hot carrier induced degradation (also called Record data
HCI or hot carrier injection) can be seen on both NMOS and No Yes
Fail/Exit
PMOS devices and will affect device parameters in all regions,
such as V T, sub-threshold slope, Id-on, Id-off, Ig, etc. The rate of
degradation of each parameter over stress time depends on the Figure 2. Typical CHC test procedure
device layout and process used.
Stress bias conditions are based on worst-case degradation
Vg
bias conditions, which are different for NMOS and PMOS FETs.
Typically, for drain voltage stress, it should be less than 90% of
Poly-Si Vd the source drain breakdown voltage. Then, at the drain stress