The purpose is to etch a straight trench of 1.8 microns on SiO2 surface. I would like to minimize the undercut. I read online that adding some Ar to SF6 would minimize the undercut (such as SF6 60sccm / Ar 10sccm) but I am not certain. Is there anybody having different suggestions?
Hi YinXiao Li,
May I ask at which pressure you are etching? In general you will get more directionality of the etching species when pressure is low. Typical RIE etchers for such purposes etch at around 10-50 mTorr. With this you will get straighter trenches. Adding Ar will only help when you have low pressures. Ar+ ions will help directionality and it is know you get a synergistic effect from the physical bombardment (Ar) and chemical etching (SF6). For this see famous article of Winters et al.
Hi Peter,
Thanks a lot. That was very helpful. The pressure that I want to try is 25~30 mtorr. To start with, I will try 25mtorr, SF6 45 sccm, Ar 10sccm and see how it goes.
Hi Yinxiao LI,
25-30 mT is a good start for the process. My experience is that with only SF6 you might have a slow etch rate. If you want to speed up the etch try to add a little O2. You might think that it will inhibit a SiO2 etch due to recombination but O2 actually splits SF6 in SF5O* and F*+ and then in SF4O* and another F* radicals. So a series of chemical splitting reactions create more fluorine radicals which enhance the etchrate. I have had very good experince etching molybdenum with a SF6/O2 plasma. I would only add a few % O2. That should suffice to split the SF6 and then you don't get to much resist erosion (which creates a sloped SiO2 profile which you do not want). If you have further questions please let me know.
SF6 + Ar seems like a good mixture because it adds physical etching to the chemical part using Fluoride. You can also try CF4 + Ar . Etching rate will depend also on the quality of your SiO2, ie. density, defects, or even other atoms present in your SiO2. Good luck. It is indeed possible, my research lab in INRS, Canada, was able to achieve it.
hello,can you have some conclusions now?I use the CF4 20sccm+Ar 10sccm ,200W,10mTorr, has a bit larger sidewall
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