Basic filler scripts for ihp-sg13g2 open PDK

[KrzysztofHerman]

This PR contains basic filler scripts for the PDK.

The filling process can be run from the command line using a python script:

klayout -n sg13g2 -zz -r $PDK_ROOT/$PDK/libs.tech/klayout/tech/scripts/filler.py -rd output_file=./design_filled.gds design_nofill.gds   

It is mandatory to have a sealring in the design.

In order to control metal filler densities user can modify the following scripts:

$PDK_ROOT/$PDK/libs.tech/klayout/tech/scripts/macros/sg13g2_filler_Metal.lym  
$PDK_ROOT/$PDK/libs.tech/klayout/tech/scripts/macros/sg13g2_filler_TopMetal.lym

where the width, length and also the distance between the filler cells can be altered. Please respect the DRC rules related to the sizes and separation of the filler cells (sections 5.18 and 5.23 of the SG13G2_Layout_Rules_os.pdf document).

While running minimal DRC in klayout one can expect AFil.g2, M1-5Fil.h errors related to the area outside the design, where the densities are calculated. The errors can be waived.

Special thanks to Daniel Schultz for providing the scripts.

[dnltz]

@KrzysztofHerman just verified the metal fill scripts again. No fill outside of the sealring and no fill violations!

[KrzysztofHerman]

@dnltz same here:

[joerdsonsilva]

To submit the GDS file, do I need to fix the AFil.g2 and M1-5 Fil.h errors reported by maximal DRC?

[KrzysztofHerman]

@joerdsonsilva I wrote in the description of this PR "While running minimal DRC in klayout one can expect AFil.g2, M1-5Fil.h errors related to the area outside the design, where the densities are calculated. The errors can be waived."
So please check where klayout marks this errors in you layout, it is probably mostly outside the actual design region. If this is the case you can submit it.