gds 2 and fabrication

[arun2011]

Hi all
can anyone explain how our layout output(gds2) is used in chip fabrication process, wat i understood is our gds2 file is used to make layout on photomask, and it will b used to project into wafer coated with photoresist..is it correct..plz explain the detailed process.
Regards
Arun

 

[yadavvlsi]

Right, GDSII contains layout information. This information should be transferred on wafer to create IC. This is called pattern transfer. Pattern is transferred on wafer by means of lithography. It may be photo lithography, e-beam lithography, X-ray lithography. Photo lithography is commercially used lithography. Cost of other lithography techniques is very high that make them difficult to use commercially. But they can provide better resolution than photo lithography , means they can create smaller features. For lithography we need to create masks. In case of photo lithography it is called photo mask. GDSII used to create masks that are used for pattern transferring.

 

[arun2011]

Hi
Thanks for your reply, its very helpful.
So from what you said and what i studied i am just concluding how our gds2 will be used for fabrication, if i am wrong please correct it.
Our layout in gds2 format will be first printed into the mask(photo mask in case of photolithography),(how it is printed not known for me) one layer at a time.Our wafer coated with this particular layer and on top of it a layer of photoresist(+) will b placed under the photomask.Then UV light is applied and the pattern can b formed in the wafer by process like ion implantation,etching..etc.

Please correct it if iam wrong or add more points..

Regards
Arun

 

[yadavvlsi]

For fabrication of a chip we requires a lot mask depending on number of steps. Each step requires a photo mask, as we require different patterns for different step. So different masks are required to crate different patterns. For example, in ion implantation a certain area of silicon is exposed rest of need to covered with oxide. gate oxide patterning require a separate mask...and so on..

How masks are made: https://www.utdallas.edu/~rar011300/LithographyProcess/PhotomaskMaking.pdf

If you are really interested in fabrication. I suggest you to read.
1. Microelectronics processing by W. Scot Ruska (Simple and Good)
2. VLSI fabrication principles by Soarb k. Ghandhi (Advanced)

If you have further queries or something I told which is not clear feel free to ask...

 

[arun2011]

Hi,
Thanks for your reply , I ll go thro' the document and ll surely get back to you.

Thanks & Regards
Arun

 

[dgnani]

There are extra steps between GDS and mask making:
- layer logic operations: the CAD layers undergo logic operations to generate the real mask layers
- OPC: optical proximity corrections involve very heavy computation to compensate for diffraction of light on the masks: the final mask look a lot different then the pattern you want on die

 

[yadavvlsi]

OPC is done to take light diffraction in to account. As dimensions shrinks OPC is becoming critical. If OPC is not done desired pattern and printed pattern on wafer will be quite different.!
Optical proximity correction - Wikipedia, the free encyclopedia