why insert filler cells into empty space?

filler cells

what will happen if we will not insert filler cells in empty space?

at which stage we insert filler cells and spare cells in the flow?

Re: filler cells

>>what will happen if we will not insert filler cells in empty space?

There will be power/ground open between the standard cells(empty space) and also may be nwell spacing DRC error.

Basically filler cells will make power/ground and nwell continuity.

>>at which stage we insert filler cells and spare cells in the flow
After Placement.

Re: filler cells

Thanks Arjun,

Please tell me one more thing

do we insert both filler cells and spare cells at the same time after placement?

do we do this bfore routing?

and

on which parameters we will decide how many filler and spare cells we have to insert?

Re: filler cells

Hi Jitendra,

>>on which parameters we will decide how many filler and spare cells we have to insert?
Once the placement is done (after meeting timing in P and R)you need to run command to add filler cells and tool will automatically add filler cells where ever there is empty space between standard cells

Spare cells needs to be added in the input verilog netlist itself depending upon your requirements(You can have few FF's and universal Nand gates).

>>do we do this bfore routing?
Yes.

Regards,

Re: filler cells

first of all hi to all..

iam just a bigineer in cadence tool and also in ic design this is my final project in my college

just wanted to know about 3 things if u don't mind

1)what's the different between guard ring and supply ring i mean why we need to insert them and what is thier function?

2)filler cell what u mean by nwell continuitiy and what the benefit to fill the gaps besise DRC??

3)any information about foot print ,permuting pins and abutment?

thx alot

Re: filler cells

arjun1110 said:

>>what will happen if we will not insert filler cells in empty space?

There will be power/ground open between the standard cells(empty space) and also may be nwell spacing DRC error.

Basically filler cells will make power/ground and nwell continuity.

>>at which stage we insert filler cells and spare cells in the flow
After Placement.

Click to expand...

Hi Arjun/Jitender,
@Arjun, You first answer is correct. But filler cells are not inserted after placement. Filler cells are added at last stage of PNR flow. If you insert filler cells just after placement. How will you optimize the design. I means upsizing the cells, buffer insertion.

Regards,
yadavvlsi

Re: filler cells

yadavvlsi said:

Hi Arjun/Jitender,
@Arjun, You first answer is correct. But filler cells are not inserted after placement. Filler cells are added at last stage of PNR flow. If you insert filler cells just after placement. How will you optimize the design. I means upsizing the cells, buffer insertion.

Regards,
yadavvlsi

Click to expand...

Yes, filler cells are inserted after your timing, placement opt and DRC cleanup. They are inserted to meet your utilization targets so as to avoid sagging of layers after fab and to ensure n-well continuity.

Filler cells could also minimise latchup and ensure a uniform a density for the chip before manufacturing.

fillers for density ? (to some extent ) but how it can help in latchup can you elaborate? they usually are empty cells, unless dcap fillers

Even i have heard from some people that fillers can minimize latchup bot didn't understand how....i thought latchup prevention is taken care of by tap cells.

Is the routing done on the different layer than the layer where the std cells are placed?

Are the memories placed in a different layer than is std cells? Who and how does choose where and how all the design cells will be placed?

Thank you!

@dmitryl : Yes, Routing is done on a different layer. It is the base layer on which all the std cells, macros, memories are placed. On top of the base layer are metal layers. It is the metal layers on which all the routing and connections are done.

Simranjeet Singh said:

@dmitryl : Yes, Routing is done on a different layer. It is the base layer on which all the std cells, macros, memories are placed. On top of the base layer are metal layers. It is the metal layers on which all the routing and connections are done.

Click to expand...

How many base and metal layers are present in the nowadays SoC chips? Are there technologies, which use several Base Layers on the same chip?

Are the STD Cells and Memories always placed on the same layer? What happen if they are manufactured in different technologies (let's say std cells @90nm and memories @120nm or that ever)?

Thank you!

There is only one base layer on which standard cells and macros are placed. The no. of metal layers depend on your design and technology. Since the designs are shrinking nowadays, a single metal layer cant be used for all the interconnections. Thus a lot of metal layers are used on top of each other for interconnection. The top layers are used for power routing because they are thick and and have more connectivity. The layers just below for clock routing and then bottom layers are used for signal routing. If the size of chip is small and interconnections are more such that a single layer cant do all the interconnections, then we use more metal layers. The metal layers are connected to each other as well through 'vias'. Thats how it works.

Hi All,
I would like to add my points here.

Spare Cell : ( Placed before the Placement to avail the uniform distribution)
These cells will be used if any Timing/Functional ECO has to be performed after the Tape-out. Generally these cells will be a bunch of universal gates and placed uniformly all over the chip. Lets say your chip is failed in meeting the timing requirements after the tape-out, during this time, the designers will try to fix-these violations by doing the Metal-ECOs to fix the timing. When Metal-ECO's performed, the designers will use the spare cells present in the design. The aim of this is not to add any cell for ECO fixing and thus avoid the base-layer mask re-generation ( to reduce the fabrication cost).

Filler Cells : ( Added after Routing and Timing closure, before LVS & DRC )
Filling 100% of the area with regular cells are generally impossible. We need spaces to improve the placement and routing. Once we complete the routing & achieve the timing closure, we may need to fill the empty spaces with filler cells for the following purpose.

To reduce the DRC Violations created by the base(NWell, PPlus & NPlus) layers.
Power Rail connection continuity.

Filler Cells doesn't have functionality. They have power rails, Nwell, PPlus and NPlus layers only. If we want to do any ECO's, then the filler cells can be deleted and the empty spaces can be utilized.

Rgds,
Kumar

So, does that mean filler cells play no role in latchup prevention?

---------- Post added at 11:57 ---------- Previous post was at 11:52 ----------

another question i had about spare cells is...are spare cells and GBF cells same or different?
thanx

Simranjeet Singh said:

So, does that mean filler cells play no role in latchup prevention?

---------- Post added at 11:57 ---------- Previous post was at 11:52 ----------

another question i had about spare cells is...are spare cells and GBF cells same or different?
thanx

Click to expand...

Filler cells doesn't play any role in Latch-up prevention. For Latch-up prevention, we use TAP cells.

GBF cells? I never heard of it. Please explain it.

GBF Cells are Gate Array Backfill cells. I heard a similar explanation for these cells, so thats why i asked..

Hi Simranjeet,
Thanks alot for the info. Please post more info about GBF cells if you've any material.

Rgds,

Thanks All for your comments!

But, what's going on with mixed-signal designs? Should analog cells be placed in a different Base Layer or they are mixed with digital ones?

What about the mixed-technology chips (chips, which include cells manufactured in different technologies (let's say std cells @90nm and Memories@120nm)). Are all of them also placed on the same Base Layer? Is it possible?

---------- Post added at 14:00 ---------- Previous post was at 13:48 ----------

As for the Metal ECO's, are they done manually or by tools? I mean Layout Engineers write scripts for ECO's or do it manually on the GUI or on the Netlist itself?

---------- Post added at 14:02 ---------- Previous post was at 14:00 ----------

Why LVS is needed? What does it give?

---------- Post added at 14:05 ---------- Previous post was at 14:02 ----------

Added after Routing and Timing closure

Click to expand...

What do u mean under Timing Closure, which is after Routing? What exactly done in this stage?

Thank you!

---------- Post added at 14:13 ---------- Previous post was at 14:05 ----------

What cells are usually used for the Filler Cells? Why should they have Power Rails? What's about GND?

When Layout engineers say "Mask", what do they mean?

Are Nwell, PPlus and NPlus layers all them Base Layers (or Base Layer - in single - how is it correct)?

Thank you!

---------- Post added at 14:17 ---------- Previous post was at 14:13 ----------

For Latch-up prevention, we use TAP cells.

Click to expand...

What is TAP cells? would you explain please?