Antenna Effect in VLSI – Causes and Solution

The antenna Effect in VLSI is also called plasma-induced gate oxide damage, which occurs during the fabrication process.

AntennaEffect may Come by following the Fabrication steps

• Contact Etch
• Beginning of metal deposition.
• Metal resist removal process
• Oxide Deposition
• Sputter etch before metal deposition
• Via etching and resist removal

How to avoid Antenna Effect in VLSI

Here some are of the best solutions to avoid the antenna effect during the Fabrication Process

• The first step and best way to solve this effect is to put transistor closures to each other so that we can decrease the run length.
• Use Metal jumper(Disadvantage is it increases the delay)
• Use Antenna Diode(Disadvantage is it increases the area)
• Cut the poly(CPO or Poly cut Layer). (Please do comment if I am missing any step to avoid this effect, I will add that to this blog).

How Antenna Diode will work to solve the antenna effect?

Antenna diodes are typically reverse-biased during normal circuit operation, meaning that the voltage applied across them is in the opposite direction of their conduction. This reverse bias prevents the diode from conducting current under normal conditions.

When the metal structure accumulates charge, causing a voltage increase, the reverse-biased antenna diode is designed to become forward-biased (i.e., allow current to flow). This happens when the voltage on the metal structure exceeds the reverse-bias breakdown voltage of the diode.

Once forward-biased, the antenna diode provides a low-resistance path for the accumulated charge to discharge, preventing excessive voltage levels and voltage-induced damage. The diode acts as a safety valve, allowing the charge to flow away from the metal structure and into the diode.

Where these charges will go from the Antenna diode?

Charges that accumulate on metal structures in an integrated circuit and are discharged through an antenna diode typically flow through the diode to a safe place, preventing damage. This safe place can be one of the following:

1. Ground or Power Grid: The charges go to the circuit’s ground or power grid, which safely absorbs them.
2. Local Discharge: Antenna diodes are placed close to the metal structures, so charges are discharged nearby, reducing the risk of damage.
3. Diode Substrate Connection: Some diodes are linked to the circuit’s substrate, providing a safe path for the charges.
4. External Circuitry: In complex circuits, the charges may be directed to external components designed for safe discharge.

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