Effect of Poly Depletion on C-V curves

mos2ex15.in : Effect of Poly Depletion on C-V curves

Requires: S-Pisces
Minimum Versions: Atlas 5.22.1.R

This example shows how reduced poly doping can result in depletion occuring in the poly gate under bias. This undesireable effect shows up in Capacitance-Voltage (C-V) curves as anomolies in the shape of the plot.

The effect of reduced poly doping in a MOSFET with a thin gate is to reduce drain current drive and increase the threshold voltage, since some of the voltage that should be dropped across the gate oxide is now dropped across the depletion region in the poly gate.

The usual causes of reduced doping in the poly are counter doping process flows, insufficient source-drain implant dose, and evapouration of dopant during thermal anneals due to the lack of a capping oxide.

The example shows both the band diagram and Capacitance-Voltage curve of a P+ poly gate doped to a concentration of 1e19/cm3. The program then goes on to compare the same C-V plot and band diagram for the poly gate doped to 1e20/cm3 and 1e21/cm3 by overlaying the three cases.

It will be obseved that even for a poly gate doped to 1e20/cm3, depletion occurs in the poly gate giving anomolous C-V characteristics. This can have serious consequences if the maximum value from the C-V curve is used to measure the thickness of the gate oxide.

To load and run this example, select the Load example button in DeckBuild. This will copy the input file and any support files to your current working directory. Select the run button to execute the example.