Talk:Photolithography

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Contents 1 Contact printing 2 What is EUV 3 Sodium 4 Acid creation 5 Needs figures

[edit] Contact printing

Contact printing is something that should be discussed a bit further. I am thinking maybe it can get its own article. This form of photolithography has a lot in common with nanoimprint lithography.Guiding light 17:10, 31 January 2006 (UTC)

[edit] What is EUV

EUV sources and materials for lithography currently operate at a central peak wavelength of 13.5 nm, although the spectrum should range from 5 to 50 nm (source). Guiding light 04:31, 7 January 2006 (UTC)

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I believe that EUV refers to smaller wavelengths than mentioned in the article. It would be helpful if someone knowledgeable on the subject to correct this. --Matt Stoker

[edit] Sodium

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In my experience, sodium is avoided like the plague in a fab, so I doubt that sodium hodroxide would be used for the developing step, but would expect to see potasium hydroxide there. Gentgeen 15:02, 24 Mar 2004 (UTC)

That's true, sodium is totally off limits in CMOS foundries. I've updated the article to mention metal-ion-free developers. 64.119.159.126 04:09, 25 Mar 2004 (UTC)

It is not just sodium that is an issue, but any heavy metal ions - anything that is a potential source of contamination. In some processes (non-CMOS) it may be desirable to use NaOH (Sodium Hydroxide) but ONLY if this is considered to be a necessary part of the fabrication process. Metal Ion-Free developers (MIF) (tetra-methyl-ammonium hydroxide? - from memory - needs to be checked) are available as an alternative.

[edit] Acid creation

Novolak/DNQ resist systems are made up of a backbone resin called Novolac. Novolac has a certain solubility in alkaline fluids (developer). The solubility can be decreased by adding DNQ. Upon exposure the DNQ is transformed into an ICA acid which increases the solubility to levels above that of the resin. I think it is not only the creation of an acid that makes changes the solubility. There is also some reaction/attraction between the DNQ and novolak that reduces dissolution.

The resist technology described here is based on so-called Novolak/DNQ systems. These work fine -and are still used- for wavelengths downto 365 nm. However when industry moved to lower wavelengths to make feature sizes even smaller they changed there resist technology to chemically amplified resist which has a slightly different working principle.

Chemically amplified resists work on very simiarly to photographic film. Exposure causes a change in the sensitizer creating an acid molecule, in turn upon a post exposure bake process, the acid generated cleaves the polymer creating more acid thus "amplifying" the effect of exposure. This was invented by Willson and Ito of IBM Research in the early 80's. They used acid generators originally invented by Crivello from GE, which were used for epoxy curing.

[edit] Needs figures

This article sure could use some images. Would a snap of our Nikon i-Line Wafertrak system be suitable? How about an image of a spinner? What image would most interest the kind of person who is liable to consult this article? Alison Chaiken 06:01, 28 January 2006 (UTC)

This sounds good, so long as you can get images that can be licensed under WIki's rather-broad terms. Don't forget to try to put them in "commons" rather than just en.wikipedia.org; that way, all the other language variants can use them as well.

Atlant 18:04, 28 January 2006 (UTC)

I can upload a photo of our small manual contact aligner if anyone's interested. It's definitely not a high volume machine, but it's good for device research and (I think) well illustrates the idea. Pictures: [1], [2] -- uberpenguin @ 2006-09-01 00:41Z

Appropriately captioned, the front view of your aligner would make a nice addition to the rather-barren article.

Atlant 00:52, 1 September 2006 (UTC)