USAF 1951 test chart in SVG format

[ramon]

One option for hi-res, high-contrast targets would be a semiconductor lithography mask. They tend to be chrome on glass (quartz if you pay more)

(...)

I used to get 5" masks for around €100, but that was an internal price and I did the design work. It's a commodity job though, so commercial suppliers were not much more expensive.

Hi Struan,

Please can you share with me some commercial photomask suppliers?

I already have the design files, provided by Bertho Boman. And also I have access to CAD tools and can create custom targets (for 5" squares).

I am living in Taiwan. Six months ago I found a photomask house that asked $150 for a 5". But resolution was very limited (10 microns) so I didn't ordered. (10 microns is only around 50 LPPM).

I know of commercial USAF 1951 charts in glass (2"x2") at $120 USD with high resolution 228 lppm. But I'd would like to make some 5"x5" target to test some LF lenses at 1:1.

[Nathan Potter]

I'll chime in here in response to Struans' comments. There are a lot of chrome mask shops around the world. Many do state of the art masks which you do not want or need - and they would be too expensive anyhow. I think the least expensive for you that would be adequate is a Pattern Generated image on chrome on soda lime glass. Typically these are .125 or .150 inch thick for a 5 by 5 inch size plate.

The resolution obtainable from an optical pattern generator can be as fine as about 2 µm features (250 lp/mm). That is easily enough to serve your needs. If you can stand 5 µm minimum linewidth you can reduce the price a bit more.

These type of masks are made by exposing a thin layer of photoresist to the light from the scanning pattern generator. The resist is usually a photosensitive novolak resin, very thin, over the chrome layer, and is then developed in a strong base solution to form the pattern in the resist. Then the chrome is etched in an acid bath to form the image. Much finer patterns can be made by electron beam exposure using the appropriate short wavelength radiation.

The common file needed for the pattern generator is GDSII. But a number of other file formats can be converted to GDSII. If you supply other than GDSII files I would recommend you get a blowback file from the manufacturer to assure that the file conversion was not corrupted.

Three mask houses I use:
www.compugraphics.com in Los Gatos CA.
www.photomask.com in Austin TX.
www.advancerepro.com in Andover MA.

Advancerepro (Advanced Reproductions) often has the better price but if you want 2 µm feature size I think you will be looking at $US 150 to 200 or so.

It would be wise to design a repetative pattern to cover the whole mask (or say 4.5 X 4.5 inch of pattern). Then you could assess plane of best focus using the wedge technique.

Check out the above mask facilities on Google.

Nate Potter, Austin TX.

[Struan Gray]

Hi Ramon

I myself never used a commercial house, but I know several who have ordered from www.photomask.com and were happy. I always got my masks from an in-house facility, or from the semi-commercial clean room labs attached to several of the scandinavian research universities.

I left the university a year or so ago, but at that point the in-house team were gently pushing routine users like myself to use a commercial supplier, since prices had dropped to the point that it was no longer worth their staff's time making our kind of stuff. I will contact my friends on the clean room lab staff and find out who they use for purely commercial orders - I'm pretty sure it was an outfit in Germany, which would save you VAT/customs hassles and postage.


Nate: thanks for the info. I'm sure there are others like yourself with far more experience making and using masks than I have, perhaps they'll chime in too. We always seemed to be able to get masks on a friend-of-a-friend basis so I never had to take the purely commercial route.

[Nathan Potter]

Ramon, the go to mask house in Taiwan is the Taiwan Mask Corp. I don't know their mask making equipment capability but is likely near the state of the art for the advanced Taiwan semiconductor fabs.
You need someone with relatively antiquated equipment (optical pattern generators) to keep the costs down. In the USA there are a few left who find enough business with startup companies and universities that they can maintain their business.

BTW I have occasionally seen lithography masks for sale on ebay but of course they will generally not be suitable for or designed for resolution tests.

Also note that it is not trivial to obtain useful resolution data using a digitizing device on an analog mask structure.

Nate Potter, Austin TX.

[ramon]

Thanks a lot to all of you for your help. Maybe I will resume the idea of ordering a photomask.

Here is some initial drawing I made six months ago. Don't know if anyone else has interest in making some design, modification, contribution, or maybe want also to order a mask.

http://213.251.184.113/largeformatph...4x4_Inches.dwg

http://213.251.184.113/largeformatph...4x4_Inches.pdf

This drawing contains group numbers -2, -1, 0, 1, 2, 3, 4, 5, 6, 7 and 8.
So it resolves from 0.25 lpmm to 456 lpmm (1.1 micron size).

It needs to modified. Because text witdh is around 0.75 microns (very expensive). Maybe I will modify it to resolve only until group number 7 (2 microns, cheaper) or delete text on smallest group.

[Emmanuel BIGLER]

http://213.251.184.113/largeformatph...4x4_Inches.pdf

Thanks, Ramon, for sharing those files with us.
In this PDF, there is a problem, small targets are completely clogged and un-readble. Like if it had been plotted with a broad pen, wider than the fine lines themselves. But this might not be a problem since pdf is not the native format of pattern generators, may be the .DWG file is OK.

This problem does not occur in the other pdf file mentioned above,
http://www.takinami.com/yoshihiko/ph..._test/USAF.pdf
where you can zoom up 6400% down to group 7 and still be able to resolve all finest groups.