black or crystal wax for KOH etch protection ?

[Hatice Altug]

Dear labmembers,

I am trying to etch silicon substrate of SOI chip bonded to another chip in KOH (at 80C for ~7 hours). I have to protect the sides of silicon device layer from KOH etch (it causes damage and destroys bonding). I have been told to use "black wax " to protect it but some people also suggested to use "crystal wax" (not sure if it is called like this?). 

Does anybody have experience about how to use and clean black wax or crystal wax? Or can you suggest any other alternative technique for protection in KOH etch?

Thanks for your help,

-hatice

    
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