Good morning everyone,
my current process requires a dry etch of an aluminum layer 80 nm thick, protected by a PMMA mask. The gases available are: oxygen (which is not appropriate, since it would remove completely the PMMA mask), nitrogen, argon and carbon tetrafluoride. I was thinking about trying with a completely mechanical etch by using pure argon plasma. However, I am not sure whether the PMMA mask would work with such an etch, and I cannot find anywhere datas about aluminum etch rates by using this technique. If you could link me some articles or give me some indications, that would be extremely appreciated. Thank you so much.
Dear Alessandra Canetta , my experience is mainly with Al wet etching, but there are abundant information about the dry etching of this metal, for instance the work of Hess, where he explains the chlorine-containing gases are the preferred etchants, including CF4 :
https://link.springer.com/article/10.1007/BF00633130#article-info
About the argon plasma, you could find useful the explanations and references from this previous post on Research Gate:
https://www.researchgate.net/post/Compare-argon-ion-milling-gold-and-argon-ion-milling-aluminum-which-one-is-faster-under-the-same-conditions
If your sample can stand wet etching, the common recipe for Al etchant solution comprises: 1-5% HNO3, 65-80% H3PO4 and 5% acetic acid and 10% water
(HNO3 causes Al oxidation, H3PO4 etches away the Al2O3 and the acetic acid improve wettability and acts as a buffer, while water let you adjust the etching rate at your working temperature).
Hope it helps.
Dear Allessandra,
This paper here might be quite helpful since it gives etch rates:
Article Thermal atomic layer etching of crystalline aluminum nitride...
And this one here gives some information on argon plasma etching of aluminium:
https://aip.scitation.org/doi/abs/10.1063/1.351990?casa_token=cKiIMAu1NvUAAAAA:gWb1Xza0Rdlho9lwuIh35bbks1L8KmVrjUrfgLgK1NzPdtqaMerjrdhT_G3RIUuAbfxkRrDtZVo
Best,
Christoph
Hi,
This completely depends on what type of plasma etch process you use for the Al etch. In short, there is no straight answer to this and this completely depends on the etch process you use. it is normally a slow process. the etch here is my opinion:
- IBE: In case you use ion beam etch process, this can yield a higher etch rate than a typical physical plasma mode etch process. what is also worth noting that since IBE is more of a physical path etch process, you can expect high sputtering yield and may be more surface damage, I dont think you will want this process for Al etch. You may use it for roughening the surface though. it can vary on what grid voltage, plasma density, bias power and platen tilt angle you use.
- RIE/ICP/CCP: again, if you use an RIE/CCP/ICP type plasma process but only with an Ar, and where a wafer sits flat under the plasma, you may increase the plasma density to improve the process uniformity, increase the bias power to increase the ion bombardment energy on wafer surface, but even this will result in more of a wafer damage than a uniform etch rate. so again a very slow etch rate and depends on bias power, icp power, temperature etc....
Finally, if you want to achieve a higher etch rate, you can use Cl based processes (BCl3,Cl2,SiCl4) and add Ar to add some degree of directionality to the process and may improve some process uniformity.
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