metal density at chip level.

[manruru]

density of all metals

hi.... i have one more question here....
why do we fix the desity at full chip level to a max and min value.
what happens if i have the metal density(%) greater than the maximum(%).

 

[Paramjyothi]

why metal density for chip

Hello,
It wont clear DRC....and also result in breakage of devices due to high metal density...
Paramjyothi

 

[selvaraja]

density unit if a metal

the metal density(%) cannot be more than maximum value

 

[manruru]

metal chips density

consider you have got waiver for the density or you have ignored it or u r DRC does not check u r density ...meaning u have a separate check for density....
what happens if you did not meet the required denisty.that means you have the density less than the required. what happens if you have teh density more than maximum... too many question right need a solution......

 

[Paramjyothi]

metal density values

Yes you have a separate density checker option or switch in DRC, which checks for density of Diff, Poly and all Metals. There is a min & max % of density for all them and density is being calculated based on segments of area based on the design & the technology.

Ex: In TSMC 130nm the metal density is calculated per unit 200x200um area, Say your design 90x100um, then it calculates for 200x200 and gives out errors for your design. This error can be cleared by Metal fill.

For max % density value is usually very high and is always met.

The density should be met because it is related to Reliability issues, Performance and Yield of the chip. So proper functioning of the devices this should be met.

 

[leo_o2]

chemical density of metals

I think exceeding max metal density will lead to yield problem. Possibly some metals won't be removed enough.

 

[jecyhale]

metal density on one chip

hi.... i have one more question here....
why do we fix the desity at full chip level to a max and min value.
what happens if i have the metal density(%) greater than the maximum(%).

I think it is better have the metal density greater than the density requirement.

If you make it less then the requirement, chip has a chance to be failed.

So I believe there is no maximum limit.

 

[manruru]

what metal has density of 9?

thank you all for giving me the answers......

 

[dalraist]

maximum density rules for cmp

Minimum metal density has to be met in order to avoid plasma etching saturation. When metal layer is built, they usually use this method to remove exceeding metal.
However, there may be a maximum metal density too. Metal regions are subject to thermal expansion. So, if you have high metal density, the dilatation may break the insulator causing shorts or chip failures.
That's why many fabs do maximum metal density DRC check too.

 

[Riad KACED]

minimum metal density layer

Hi,

No that is false, having density above maximum is not good at all, it is even worse than having it less than min.

You really need to stick at the min/max bounds.
If you have too much metal, than the dielectric between metal tracks is most likely to get missed during the etching stage. This would lead to a collapse of the metal wires on each other resulting in very nasty shorts.

If your chip is meant for few samples, than your process engineers can make some effort taking extra care of what is going on. This would not be possible for mass production chips. All density rules have be fixed.

In terms of CAD implementation, it really depends on the process and the PDK provider. The check could be either part of the initial DRC check or by switching an extra button/file. Density checks are window-based as well. The size of the window could vary from a process to an other.

In more advanced technology nodes like 65nm and beyond, density checks are getting even tough ... There are rules to make gradient checks between adjacent windows, other rules to check density over multiple metal levels ... quite a nightmare really ... But this is very important for DFM and Yield. Yield is money ;-)

Cheers,
Riad.

 

[vijay.kumarreddy]

metal density in a chip

This is the main reason for the dummy metal fill:

Chemical mechanical polishing (CMP) has been used in recent years to planarize interlayer dielectrics. CMP processes are sensitive to layout patterns and this can cause certain regions on chip to have thicker dielectric layers than other areas due to differences in the underlying topography. Under such circumstances, metal fill has been found to be one of the most commercially viable options in reducing layout dependent dielectric thickness variation. Metal-fill patterning is the process of filling large open areas on each metal layer with a metal pattern that is either grounded or left floating, to compensate for pattern-driven variations. Metal fill most certainly adds parasitic capacitance. It is important to enable designers with a realistic estimate of the parasitic capacitance caused by metal fill insertion.

 

[lsimeon]

full chip level

what happens if i have the metal density(%) greater than the maximum(%).

--> it can cause the components to be shorted if it is not properly etched... also may cause the overall impedance of the device to lessen... and the overall capacitance to decrease...

 

[smihaan]

max/min metal density

CAN WE WAIVE OFF MAX AND MIN METAL DENSITY ERRORS WHILE RUNNING DRC?

 

[leo_o2]

tsmc metal density

It is better not to do so. Exceeding Max density will lead to that metal can't be etch off as expected. Less than Min density will lead to over-etching.

 

[deepak242003]

index of metal density

MInimum metal density rule:The difference in oxide heights
for a given region on a design called Planarity and is an important factor affecting the
wafer yield. When a design has regions of low metal density, the oxide layer can sag
considerably. Polishing does help improve planarity, but if metal density is particularly
low, the amount of oxide sagging can be too great to overcome. Metal fill is required to
maintain a uniform metal density across the chip on each layer and thereby ensure
planarity during the chemical-mechanical polishing process. So there is minimum metal density rule.

Max metal density: thermal expansion of metal limits the max density of metal.