Colbhaidh said:You should use dummy metal filling until you get a density of > 25% - a requirement for the metal etch processes in the fab. The dummy metal need not be connected to anything but do not place dummy metal over critical analogue cricuitry or any matched components (eg current mirrors etc)
wee_liang said:Hi,
Just for sharing. In my experience, there have been reports of damages on IC for large floating metal dummies. Most of them caused by discharging of static charges on these metals during CMP process. Through microscope, it was seen clearly a big "bomb" (i.e. burnt marks) was shown on certain ICs with large floating metal.
My recommendation is to keep it grounded if not too painful to do so.
Colbhaidh said:CMP cannot itself cause any damage. This process leaves about 1um of more of TEOS above any metal lines. Any damage must have come from an ESD event where metal is exposed at the surface of the chip (metal etch etc) or after completion during assembly or something.
During Fab processing, if the metal lines are connected to any substrate diode (eg N+ or P+) then electrostatic static charges that may be evident during processing will be connected to the wafer substrate through the relevant diodes. This means there is no potyential between the metal and the substrate so no damage.
However, even leaving them floating, modern processing does not leave residual charge on the surface (or should not). Also, dummy lines should be placed over field isolated areas so if there was any charge, it could not damage anything.
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