I have successfully released MEMS cantilevers with a photoresist sacrificial layer, using a dry plasma ashing technique. However, this process tends to damage the metal contact pads and result in curved beams. To rectify this issue, I have attempted to perform a wet release process with critical point drying. The die is placed in a remover PG bath (heated 90C, for 3 hours). Then it is placed in IPA and followed by critical point drying. When the process is done, all the cantilevers on the die are cracked at the anchor point and no photoresist is removed.
What can be the possible reason for the cracking?
appreciate any responses.
hi Shankar Dutta thanks for your response. Can you elaborate further regarding how the residual stress may crack beam at the anchor point?
I imagine there are indeed residual stresses in the bilayer beam, because when the device is released using a dry plasma ashing, the beam curves upward which is indicative of this stress relaxing.
Hello Kissan Mistry ,
Can you please tell us that which photoresist you are using (Positive or Negative)?
The mismatching of thermal coefficients of PR and contact pads/anchor points leads to the crack formtaion on the pads after/during release. Since, you are heating the cantilever at 90C for 3 hours, which is quite long time.
I hope this may help you.
Best regards,
Varun
Dear Kisan Mistry.... please see the following article: https://www.researchgate.net/publication/325223352_Effect_of_residual_stress_in_Pb_Zr052Ti048_O3_-_BiFeO3_multilayer_cantilever_structure?_sg=r4A14cVXM1hgDQyDLKFzohnAo_5XbcqmVwnrVzcO6ROUATfQukYFNBqs-doxGOnFhrZIiW6QbhZFMH15aMkKUKTOnPMvos5XCe2RMlCG.UHz36aZzRvOzqvmBilDdhcEP8bl4Lhs8mZfwBynHY7FepfBzVmjQzpMh2IQ0g79xAhC89xGwElGkIcs55flfAQ
hi Varun Pratap Sharma thanks for your response. The sacrificial photoresist is positive (Shipley S1800). I understand your point, but i do not have this crack issue when i a use a dry release method such as oxygen plasma at a high temperature of180°C for 4+hours. So it is strange that the wet release resulted in cracks.
hi Shankar Dutta thank you for your paper.
I understand that there are residual stresses in the bilayer beams, infact i expect it. however, what i dont understand why a dry release process (through oxygen plasma) results in no cracks while, a wet release process (with critical point drying) resulted in cracked breams?
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