Two-step anneal trial
Last week I mentioned that a two step anneal may help with the tears that are forming on the membranes when they are annealed post-etch. The recipe I used was a 10 C/s ramp to 600 C, hold 60 s, 10 C/s ramp to the setpoint, hold 60 s, ramp down. I annealed membranes with and without protective oxides. Unfortunately, this recipe induced wrinkles over parts of the membrane.
The left panel shows membranes that were annealed without protective oxide. Although there are no signs of tears, part of the membrane is wrinkled. I believe that the intermediate anneal at 600 C is partially crystallizing the film putting it in a lowest energy state (partially wrinkled). The second anneal is unable to knock the film out of this state thus leaving the membrane half-wrinkled. Another possibility is that the membranes are partially oxidized. I should note, though, that in my previous one-step anneals, the highest temp I have had success with was 800 C; with the two-step I can safely ramp to 900 C.
The right panel shows two membranes that were annealed with protective oxides on and then subsequently stripped after the anneal, the top: a one-step anneal to 1000 C; the bottom: a two-step anneal to 1000 C. Sadly, both these membranes have tears. The two-step anneal sample also shows partial wrinkling of the film.
My next step is to lower the intermediate anneal temperature so that the film doesn’t crystallize as much which will hopefully get rid of the wrinkling.