Add screenshots of cross section outputs

[mithro]

It would be nice to have some screenshots of the output from the cross sections and compared to the diagram at https://skywater-pdk.readthedocs.io/en/main/rules/assumptions.html#process-stack-diagram and in Tim Edward's presentation at https://isn.ucsd.edu/courses/beng207/lectures/Tim_Edwards_2021_slides.pdf

[mithro]

There are also some SEM images of cross sections available at https://drive.google.com/drive/folders/1g1bbKXEHyT3X1R70beO_45QzWtwWS_Ky

[klayoutmatthias]

I'm honestly not sure about the quality of the XSection output. Specifically in the frontend part my reasoning was that Sky130 would be a shallow trench isolation process. The stack diagram does not reflect this.

[mithro]

Some optical images where recently posted at https://x.com/johndmcmaster/status/1715863105782378529?s=20

[mithro]

I think the output would be better than random hand drawn diagrams that exist?

[mithro]

Some foundry provided cross section diagrams can also be found at https://skywater-pdk.readthedocs.io/en/main/rules/device-details.html#details

[klayoutmatthias]

The point is: the cross sections from the device details are not consistent with the stack diagram regarding the frontend part. The device details indicate shallow trench isolation for example while the stack diagram does not. My images are based on my guessing and gut feeling. The SEM images are not good enough to decide that and implants cannot be visualized by SEM anyway.

In that sense the cross sections from the script are rather virtual reality unless there is some kind of confirmation.

I'm saying that because it's very easy to draw wrong conclusions from incorrect cross section drawings. In the worst case, parasitic junctions are not considered properly and functionality is compromised or latch-up happens.

Matthias

[mithro]

Don't know if it helps, but a complete list of the steps in the SKY130 process can be found in the spreadsheet @ https://docs.google.com/spreadsheets/d/1PbI3IVNg93fR9Gi_hXlEDrlYtwFQuMyaD8PNEaIs3Sg/edit#gid=363070671&fvid=1378094797

[mithro]

FYI - I have been collecting information about the metal layers from the "Cypress Semiconductor Product Qualification Report". You can find it at spreadsheet at https://docs.google.com/spreadsheets/d/1ZB5XAwMF3zlGX8tET1-uyaFlDqHhBxabQ04PQGYwjZo/edit#gid=0 and https://docs.google.com/drawings/d/1wWBi4lQcLCZRgwqdpY8LDtjc-cHvMiD8_fxv4Ly46s4/edit

See also below;

[mithro]

So the S8 / SKY130 Process Steps spreadsheet has steps called "Shallow trench nitride etch" and "Shallow trench etch" (also shown below), so does that mean it is using shallow trench isolation?

#	Step	Description
1	SMAT	Starting material
2	BOX	Base oxidation
3	ISONIT	Iso nitride deposition
4	FOM	Field oxide mask
5	STINITE	Shallow trench nitride etch
6	STIE	Shallow trench etch
7	DNM	Deep N-well mask
8	DNI	Deep N+ implant
9	DNIS	High V deep N-well implant strip
10	LINOX	LINOX oxidation
11	FILOX	Fill oxide deposition
12	CMPNIT	CMP over nitride
13	NS19	Nitride strip
14	LVTNM	Low Vt NOMOS mask
15	LVTNI	Low Vt NOMOS implantation
16	LVTNIS	Low Vt NOMOS implant strip
17	NWM	N-well mask
18	NWI	N-well implant
19	NWI2	NWI2 implant
20	LVTPI	Low V P-channel implant
21	LVTPIS	P-channel implant strip

[klayoutmatthias]

I'm not really an expert, but I think that is pretty much the flow of a shallow trench isolation process. The CMP with step 12 will basically planarize everything, leaving active area islands for the devices and STI regions for the space between them.

So I guess my cross section images are basically correct, but the cross section in the design manual makes less sense.

Matthias