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Antenna Effect

Antenna Effect:

    Process antenna effect or “plasma induced gate oxide damage” is a manufacturing effect. i.e. this is a type of failure that can occur solely at the manufacturing stage. The gate damage that can occur due to charge accumulation on metals and discharge to a gate through gate oxide.
    Let us see how this happens. In the manufacturing process, metals are built layer by layer. i.e. metal1 is deposited first, then all unwanted portions are etched away, with plasma etching. The metal geometries when they are exposed to plasma can collect charge from it. Once metal1 is completed, via1 is built, then metal2 and so on. So with each passing stage, the metal geometries can build up static electricity. The larger the metal area that is exposed to the plasma, the more charge they can collect. If the charge collected is large enough to cause current to flow to the gate, this can cause damage to the gate oxide. This happens because since the layers are built one-by-one, a source/drain implant may not be available for discharge as in fig.
    Antenna rules are normally expressed as an allowable ratio of metal area to gate area. Each foundry sets a maximum allowable antenna ratio for its processes. If the metal area–which is cumulative, i.e. the sum of the ratios of all lower layer interconnects in addition to the layer in check–is greater than the allowable area, the physical verification tool flags an error.For example, let’s say maximum allowable antenna ratio for metal1 is 400. If the gate area is 1 sq.u and if the metal area connecting to the gate is 500 sq.u, there will be a process antenna violation.
    1) Jumper Insertion Technique
    2) Reverse Biased Diode Technique


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