What exactly is a dummy metal fill ?

[rahultcd]

To account for copper's side effects, physical design tools insert dummy metal patterns, called metal fill, so that designs meet the required metal density " as specified by foundries " to reduce the thickness variation.

WHat is exactly this dummy metal ? wher it is connected ?
Can somebody explain how exactly this dummy metal fill, help to minimise thickness variation ..?

thanks
...............

 

[guru010]

dummy metal fill ?

Dummy metal fill is to satisfy the metal density for paticular area. If the density is not satisfied for a metal than it leads to Sagging of metal and leads to yield problem.
If we draw a big rectangular metal to satisfy density and didn't followed slotting rules these leads to over density in paticular area.
Dummy metals are left floating which are filled by the tool and if you have filled manually then better to connect GND supply.
Coming to thickness variations I don't have better IDEA.

 

[roadbuster]

Re: dummy metal fill ?

There are two major reasons for using a dummy fill:

1. Strong acids are used to etch layers of material during fabrication (eg: metal). If there is not enough metal in an area of the chip, the acid can begin to etch-away at other materials on the chip

2. When you fabricate the chip, you are building multiple layers on top of eachother. The total height of the chip can vary in different areas based on the material layers in that region. If you do not have enough metal in a certain area, the chip's height will "sag" in that area. This causes problems during the build-up of higher metal layers on the chip. You can see the variation in chip height in these diagrams:

**broken link removed**
**broken link removed**

The dummy fill is typically left floating (ie: connected to nothing).

 

[rahultcd]

Re: dummy metal fill ?

Thnks

I understood ur points.
But the dummy Met fill tht u r talking is remedy fr removing thickness variation due to absence of metal.

But I was refering to dummy Met fill , which is used to compensate fr -ve effects produced by CMP (chemical-mechanical polishing).
Now Read following ..

"" For copper, the pattern for the metal traces is etched into the
ILD and copper is electroplated into the newly created trenches. The excess copper material is removed in
a chemical-mechanical polishing step. As a result of this process, variations in wafer height may appear in
areas where the metal density is not uniform.
*(1) Areas where wide metal lines exist can experience erosion, a
condition where too much copper material is removed.
*(2) In locations where the space between metal lines is
smaller, dielectric dishing can occur. The result is greater electrical variation

So To correct for planarity issues, rule-based metal fill is a common approach for inserting dummy metal fill to
achieve uniform metal distribution and adequate planarization ""

Question :: so I m not understanding how excess dummy fill is helping to resolve the problems (1) & (2) ??

Thnks..

 

[rahultcd]

Re: dummy metal fill ?

Any comments ?

 

[varma_cs012]

Re: dummy metal fill ?

rahultcd:

He didn't say excess metal fill going to reduce the problems. He only says rule-based metal fill is going to reduce the problems. So now please repeat your question, we can discuss on this!

 

[rahultcd]

Re: dummy metal fill ?

Thnx,

But after all it is metal fill, whether it is rule based or not , it will have same effects ...

plz Read Q properly ..

thnx

 

[rahultcd]

Re: dummy metal fill ?

Any reply

 

[SP24]

Re: dummy metal fill ?

I recommend u to view the attachment in this link(slides 25-29)

 

[rahultcd]

Re: dummy metal fill ?

thnks..

I got some idea./understanding

Regd