What are the rules of metal density?

[vlsitechnology]

Can anyone explain me about the rules of metal density...Why do we need to check and what is the purpose?
Why ,Why,Why...go as much depth as u can bcz its been asked by the INTEL company...........

What is the difference between BJT and CMOS at the circuit level?? features and advantages............

Please explain all these things in detail

 

[layoutmaster]

metal density rule

Are you talking about metal's CURRENT DENSITY or CHIP's COVERAGE DENSITY?

 

[vlsitechnology]

metal density

I am not talking about current density that is different

 

[layoutmaster]

design rules for metal density cmos

okay then, if you meant metal coverage density it has to do with fabrication process issues.

It´s a requirement for the metal etching process, and it's because the used plasma is too sensitive to the qty of resist material (in other words, the density). Process usually check between 25 or 30% to 70 to 75% in order to make sure the etching is done properly.

A different chapter is if you're between the approved percentages but a particular area is having a density beyond the limits...

 

[vasantha]

metal density rules

As far as metals are concerned, there is a need to ensure the nechanical sturdiness of the chip as a whole (even though it appears small). Other reason is to achieve a smooth planar structure for different metal layers so that all metal layers are uniform in structure and performance. If the metal density is not good some metal layers may be more in height than others and hence the timing, EM, power integrity may be affected.

 

[vlsitechnology]

metal densities google

Yes thats true layout master but wt exactly we will do in the layout stage to achieve particular metal density?? Or the tools does it ??...Do we have any role there?

Reply me

 

[layoutmaster]

rule metal density

It depends on the process...

SOme will require your manual additoin of dummy metal poligons in order to reach teh allowed coverage percentage.

Other processes have special scripts that check the coverage and then automatically add polygons in the layer not reaching the approved % by following some initial constraints set by the layout designer.

So the difference is if you just run an script and wait for the result or if you need to manually do the complete job but in all of the cases you must check the coverage becuase having everything inside the approved % will be a requirement from every fab.

 

[vlsitechnology]

metal density 16

How do we know that we are reaching the allowed coverage percentage? which u said in the first point..?

 

[layoutmaster]

what if the metal current density beyond

That depends on how is metal density check done within the process you're using.

Sometimes is included in the standard DRC check, sometimes is an alternative DRC check (with a "Density check" switch turned on) and sometimes is a different check

 

[kumar_eee]

density for all metal

Metal density violation is rectified during the DRC cleaning process.

 

[punnu78]

density rule in cmos

for febrication we need some metal density for uniform metalization during febricaion.
So fab defines density rules.
but we needto worry only during top level

 

[selvaraja]

density rule in cmos fab

Bipolar vs. CMOS (performance)
Compared to CMOS, bipolar transistors
o have lower parametric variance
o can operate with higher supply voltages
o have higher device gain (higher rout)
o can operate with higher output current density, and thus lower
o parasitic capacitance for a given current
o maintain current gain over decades of collector current
Therefore, compared to CMOS, bipolar amplifiers
o have lower untrimmed offset
o support higher voltage swings
o can drive resistive loads with higher bandwidth