http://www.righto.com/2024/11/antenna-diodes-in-pentium-processor.html
I was studying the silicon die of the Pentium processor and noticed some puzzling structures where signal lines were connected to the silicon substrate for no apparent reason. Two examples are in the photo below, where the metal wiring (orange) connects to small square regions of doped silicon (gray), isolated from the rest of the circuitry. I did some investigation and learned that these structures are "antenna diodes," special diodes that protect the circuitry from damage during manufacturing. In this blog post, I discuss the construction of the Pentium and explain how these antenna diodes work.
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Antenna Diodes in the Pentium Processor
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(Score: 2, Informative) by Moof123 on Friday November 29, @02:44AM
Antenna diodes are one solution, another to mitigate the need for excessive antenna diode area is to use “jumpers” near the gates. If you briefly route to a higher metal layer, then back down. The goal is to minimize the metal area to the gate area for otherwise floating sections of wire. By creating a gap in say metal-2 near the gates the processing of metal-2 requires either no antenna diode, or only a small minimum sized one. Processing metal-3 would only have a short run of exposed metal tied to that gate, again mandating little or no antenna diode area.
A best practice when building up a sub-block is to put a small antenna diode and then a jumper as you exit the inputs (gates) of the block so that you don’t risk having new design rule violations as you route to the block at the next level of hierarchy up.