Hellmanex III creates liftoff membrane?!?!?
While I have been in Montreal with Albert Kamanzi and Sabrina Leslie, Albert mentioned to me a cleaning protocol that appears to strip off NPN.
- 5 mL of Hellmanex III in 100 mL of DI water
- Placed in heated water bath, covered with parafilm (setting 50C, actual 40C) for 2 hrs
- Delaminates NPN?
The chips are mirror-like afterwards, indicating that they have been etched/stripped. The chips experience a color change around 1 hour, turning from tan to blue. I believe that the ‘etchant’ is attacking and undercutting the NPN even in the bulk regions.
This is interesting, as the Hellmanex III MSDS ingredients are:
- TRIPOTASSIUM ORTHOPHOSPHATE ; EC No. : 231-907-1; CAS No. : 7778-53-2, Weight fraction : ≥ 15 – < 30 %
Classification 1272/2008 [CLP] : Skin Irrit. 2 ; H315 Eye Irrit. 2 ; H319 STOT SE 3 ; H335 - phosphates
- anionic surfactants non-ionic surfactants
I was surprised to see how evenly it lifted off. Perhaps we can use this in conjunction with a SU8 backbone and make the curls more like sheets? I’m going to bring a few dried pieces back with me for SEM.
This is a mildly alkaline solution (like KOH, but weaker). So it is not surprising that the SiN lifted off after 2 hours. The SiN itself should be unaffected by this, the color change could be solely due to the undercutting of the Si. Keep in mind that the distance between pores is only ~100nm at most, so it does not take long for something to lift off.
As far as trying to use this, its highly impractical. XeF2 will liftoff a 1 inch piece of np-SiN with a single pulse (if no SU8 is present) and BOE does so in about 2 min (or 60X faster than this solution). And it would take weeks to liftoff anything with SU8…100nm vs 17um of undercut….