I have 250 nm (top silicon over oxide) thick SOI. I want to create slot of 200 nm width and 250 nm height. What is recipe of patterning mask using EBL over the SOI? Will it be better to use PMMA photo resist for this purpose? After the EBL process, what recipe of RIE should i use? If you have any idea or research material for this, please share. It will be great help for me.
Thanks in advance
Hello, since you want to etch silicon with aspect ratio structure above unity, I think you need to use the Bosch process (chlorine based RIE) for etching silicon. If you do not have access to Chlorine then CHF3 or SF6 based RIE can do the trick. In that case you need to use an "intermesh" of aluminum to protect silicon better than resist. in that case you use standard resist, evaporation of Aluminum mask through the pattern you want to create and lift off of aluminum. After RIE the aluminum can be removed by some specific etch.
Hello,
If you need to etch Silicon with PMMA as a mask while stopping on the oxide, HBr-based plasmas are the best suited. With more standard gases like SF6/CHF3 as mentioned by Mr Bouchiat, you can mix both gases to achieve some selectivity but ICP are better suited than CCP reactors (sometimes called RIE but it is very misleading). If you only have access to some CCP reactors, then try low pressure moderate power SF6/CHF3 mix.
If you want to reduce mask consumption while still using PMMA, then use PMMA with high molecular weight.
I hope it will help.
Best Regards
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