I'm having some problem with the hard bake of the resist and I wonder if someone could help me with that.
Initially I make the adhesive coating followed by prebake and the resist coating with the thickness of 8µm (Speed: 2800 rpm, Acceleration: 2000 rpm/s and Time: 25 s) and I prebake it at 100°C for 9 mins with hot plate.
Then I develop with AZ 351B (1:4) for 4.45 mins and I hard bake it at 115°C for 60 mins. I proceed with reactive ion etching (RIE) after hard bake.
The problem with the process is I notice re-flow of the resist after hard baking which is really bad. So I would like know the optimized condition either with the hard bake temperature or the baking time or any other possibilities.
Regards
Uma Muthiah
Dear Uma, the softening point of the AZ4562 resist is 110C, so you are allready above this causing the resist to reflow. You might perform the hardbake at 100C for longer time.
Hello Mr.Wijnperle
Thank you very much for your time in answering my question. It was helpful and I'll give a try.
I'm not sure about that resist specifically, but a 60 min hard bake is a long time even at 100C and I feel like reflow would still occur. One thing I do is to use a shorter hard bake in a vacuum oven. I do 15 um of AZ4620 for my etch masks, and a 10-15 min bake at 90C in a vacuum oven gives me the best results.
While your developer is not explicitly mentioned in the technical datasheet ( http://www.microchemicals.com/micro/az_4500_series.pdf ), it should do. I'd suggest to meticulously follow the recommendations in the tds - especially about evaporation time prior prebake. According to the tds a postbake of 50 seconds @ the 115 °C hotplate will suffice.
What seems to be a common misunderstanding of the term "...bake": it's not about baking some cake! It is about getting rid of solvents and about "annealing". So during "hardbake" some flow is to be expected - softening the edges where the removal occurred. BTW: your prebake time is way beyond what's recommended although in this stage it should not hurt.
Thank you very much for spending time in answering my question. It was helpful.
I used the same resist AZ4562 (typically 5 microns thick) in a number of projects and often as an RIE etch mask. My processing goes as follows: (i) spin HMDS adhession promoter, bake at 110 deg C for 1-3 min, spin AZ4562, bake 110 dec C for 3 min, exposure, development in AZ400K:water (1:4 volume) for 1-2 min until structures are cleared. I do not use post-bake because that would reflow the resist. If I use other much thicker AZ resists that do require post-exposure baking (to remove the solvent or otherwise the resist will bubble and "boil" in the hot RIE reactor), such AZ40xT, then I bake in a vacuum oven at 90 deg C, usually overnight or at least 12-18 h. Good luck with your processing.
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