antenna metal fill concepts

8/6/2019 Antenna Metal Fill Concepts

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Time To Market Inc 1

•Time to MarketR A M

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Antenna & Metal Density

Concepts:

Venkata Simhadri

Time To Market Inc





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What is Antenna ?

( When metal layer is being deposited, electro static charge(ESD)

gets collected on the wires, which can destroy the device and

make chip useless. This is called ‘Charge-collecting antennaproblem’.

( Antenna problem is usually caused by dangling metal pieces

extending from the input pins.





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How to protect your chip from Antenna ?

( Minimising ‘the Antenna area’ by breaking the wireswith contacts and wires in other metal layers.

( Inserting extra diodes to protect input pins.





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Antenna Rules

There are 3 major factors in computing antenna rules:

( Antenna recognition – 3 modes

v ignoring lower layer segments (mode 1)

v including lower layer segments to pins (mode 2 )

v including all lower layer segments (mode 3)

( Side-wall area versus polygon area

v side-wall area of metal is used

v polygon-area of metal is used

( Protection from diode and output pins

v diode and output pins provide unlimited protection





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Antenna Recognition

( Mode 1 : Ignoring lower layer segments

v For metal1 antenna, it counts all metal1 wires between

input gate and first metal2 while tracing from input pin

v For metal2 antenna, it counts all metal2 wires between

gate and first metal3 piece while tracing input pin

v Similar rule applies for all metal layers.





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Antenna Recognition - Contd..

( Mode 2 : Including lower layer segments to pins

v All antenna area from ‘mode 1’ plus all the upward metalpieces from input gate to ‘mode 1’ antenna

v A metal piece is upward if all wired between the input gate

and itself are no higher than itself





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Antenna Recognition - Contd..

( Mode 3 : Including all lower layer segments

v All antenna area from ‘mode 1’ plus all metal piece between

‘mode 1 antenna and input gate

v most conservative method of computing antenna

v most difficult and expensive to fix





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Side wall / polygon Area

( For W x L metal piece counted as antenna, there are 2ways of computing antenna area:

Side wall area = (W + L) * 2 * thickness

Polygon area = W * L





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Protection from diode and output pins

( Unlimited protection :

v The input is considered safe once it is connected to adiode or output pin

v Because input pins are always connected to some outputpins through the highest metal layer of the net, the highestmetal layer of nets always meets antenna rules

( Limited protection :

v When input is connected to a diode or input pin, it canallow a higher antenna-to-gate ratio.

v All layers including the highest metal layers of nets needto be checked

v Limited protection rules are required for <0.18umprocesses.





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Filling and SlottingWHY?

To make these effects uniform and predictable due to the Varying

effects of manufacturing on device and interconnect features

Processes such as:

Optical exposure

Resist development

Etching

Chemical vapor deposition

Chemical-mechanical polishing (CMP)





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Metal Insertion - Filling

Partial Deletion - Slotting

Effects On:

RC extraction

Delay calculation

STA

Noise Analysis

antenna metal fill concepts

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