Annealing w/o protective oxide
Here is a summary of results for membranes (w510X) that have been annealed without their protective oxide.
800 C RTP @ 10 C/s in susceptor
850 C RTP @ 10 C/s in susceptor
900 C RTP @ 10 C/s in susceptor
950 C RTP @ 10 C/s in susceptor
It seems that annealing between 800 C and 900 C does not yield any through pores; only texture (now confirmed by Jess’ AFM post). At 950 C, the membrane oxidizes and shatters. Interestingly, the EM shows the formation of pores as well as nanoscale tears at this temperature. It appears that without the surrounding oxide during anneal, there is no constraint on the silicon which allows for tears to form.
Annealing without the protective oxide does not seem to be practical for making membranes with pores, but further investigation into lower temperature anneals (700 C) are being performed for TEM grid applications.
Makes sense.
The optical micrographs of the 950C sample are interesting. I’ve never seen a broken membrane that’s 15 nm thick remain this intact. I’ve only seen 200nm – 500nm films crack like this. There must be very little stress in the films.