Thank you for your suggestion. We already use PMMA in various variants for other applications and process modules. But for certain "litho+dry etching" modules we definitely need ZEP resist as its etch rate can be significantly lower than that of PMMA for some etching processes.

Well, let's say that PMMA is a good first guess when it comes to the worst mask for dry etching with certain gas mixtures.

You are also right that with other gas mixtures process parameters can be optimized to achieve lower PMMA etch rates, and for those processes we routinely use PMMA etch masks with such optimized processes. But for some other etching chemistry PMMA is simply not a feasible option. Not only due to its high etch rate but also due to increased line edge and line width roughness and other figures like that.

Have you thought about using HSQ as EBL resist and hard mask for etching processes? HSQ is a negative tone EBL resist, which becomes silicon dioxide-like after lithography and baking. It makes a good etch mask in most of dry etching standard processes.

About PMMA: the selectivity to the substrate depends of course on plasma chemistry and etching recipe, but in my experience, using PMMA I never reached values better than 3 by respect to silicon.

Have you tried contacting ZEON here @ http://www.zeon.co.jp/contact_e/index.html

Dear Gianluca, thanks for your suggestion regarding HSQ. If you browse through my publication list you might notice that we work with HSQ quite a lot and for quite a while, this is more or less our “working horse” resist material. Whenever possible we tend to use HSQ. Nonetheless for some applications we need to use a positive tone resist like PMMA or ZEP.

There are many types, have you considered SML?

http://www.nanoscalereslett.com/content/8/1/139

Dear Rob, thanks for mentioning SML as an alternative rest material. I’m already aware of this material, but from the exposure results achieved with this material I found in literature so far this material seems to aim at different applications than those we use the ZEP resist for.

We don’t need high aspect ratios and we also don’t need a high sensitivity, but we need a very low sidewall roughness of the features and a wide process window with a very good CD control in addition to compatibility with our etching process. So far, only ZEP resist seems to fulfill all our requirements.

Hi above all.. I am trying to etch nanostructures in CMR thin films like LSMO and LCMO . All I need is 1 - 2 nm etch profile . PMMA-A4 is not surviving more than 30 sec with SF6: Ar mixture . Does anybody have suggestions to make PMMA-A4 better etch resistant ? Will coating with few nm Cr will do the job?

With a PMMA-A4 resist I take it we are talking about a resist mask of something between 200 and 400nm, right? PMMA is not the best mask for dry etching, but with more than 200 nnm you really should be able to etch longer than 30 sec. Maybe you should have a look on your etch process and try tio optimze it a bit, sometimes a small change can dramtically influence the etch rate for your resist material.

Have you considered to use CSAR from AllResist instead of ZEP? It should have (almost) same qualities and properties as ZEP520A. http://www.allresist.de/wp-content/uploads/2014/03/allresist_produktinfos_ar-p6200_deutsch.pdf

I echo Tine Greibe's suggestion of using CSAR.

At the James Watt Nanofabrication Centre (http://www.jwnc.gla.ac.uk/) CSAR gives near enough identical performance in terms of sensitivity and dry etch resistance to ZEP.

Have a read at this publication comparing PMMA, ZEP and CSAR:

Article Investigation of CSAR 62, a new resist for electron beam lithography

Dear James, thanks for your answer. We tested CSAR quite extensively a while ago. It is indeed a 1:1 replacement for ZEP520A. With CSAR, which was renamed AR-P 6200 a while ago, we can use almost the same exposure and development parameters we used for ZEP and achieve very similar results. And it costs just a fraction of ZEP and is usually delivered within a few days.

Hi all,

Jens Bolten I am wondering how is the process used for CSAR 62. Is it necessary to improve adhesion by another chemical by the company Allresist? How is going the adhesion? What are the smallest features you can get with CSAR or ZEP? I assume you use Raith, what is the dose that you apply?

Kind regards,

Miguel

As others have mentioned, AR-P 6200 is a very close substitute for ZEP, and I have had good results with it.

Hi all,

I have almost the same questions as Miguel Sánchez Lozano . I have a little experience with both ZEP and AR-P 6200 and I can say that in general I can use it as "higher process lattitude" PMMA substitution. For example, if I want to have small and even features in case of non-uniform resist thickness areas, thus performing some "overdeveloping", I prefer to use AR-P6200, because it has greater contrast and doesn't change lateral dimensions as PMMA does.

But compared to PMMA it seems that AR-P6200 has weaker adhesion to my typical substrates (mostly GaAs). Does anyone can suggest working recipe to improve adhesion? As standard I perform organic cleaning, O2-plasma in barrel asher and dehydratation 15-20 min at 180C on a hot plate. Spin coat @2000 rpm + bake @150C for 60 s

Hi all,

We've been developing a metal-organic resist which we believe has excellent etch properties. A recent paper appeared in Nano Lett., 2019, 19, 6043-6048 where we showed we could etch sub-10 nm structures into silicon and tungsten. I'd be very happy to send anyone a reprint or talk further if you are interested.