Agilent Technologies B1500A Training Manual page 107

Low Current Leakage
Gate Oxide
Leakage to fA levels
Electrical connection to wafer backside
Chuck must be guarded
Gate oxide leakage tests are complicated by the fact that there is an electrical connection to the back
of the wafer. The chuck must be insulated and guarded to get meaningful low current results. The
huge capacitance of the chuck surface would cause charging currents which would swamp out the
low level currents you are trying to measure through the oxide.
Gate
Oxide
+
Wafer backside
Substrate
6-35
Module 6
Low Current Measurement