As a kind of ceramic materials, alumina (Al2O3) is really hard to etch. Many thanks to those who can show me detailed info. of etching alumina.
Hi Yingbin
The best method to etch alumina (Al2O3) is by a standard procedure of electrochemical etching in order to reveal the microstructure characterization of the sample.
The answer to your question can be found in the reference:
https://www.asminternational.org/documents/10192/1849770/06044G_Chapter_Sample.pdf
The paper Florian mentioned gives a good overview. You must however take into account which grain sizes you expect in the alumina ceramics and with which method you want to apply make the images. We typically use thermal etching in air.
150K below sintering temperature for a few minutes is agood rule of the thumb for thermal etching.
If you use a high resolution SEM with in lens technology you should decrease the thermal etching temperature by another 50 K and etch no longer than 5-10 minutes.
With an ordinary SEM the conditions are correct, if you want to apply light microscopy for samples with a grain size of > 10 microns you may raise the temperature some 50 K above the level described in the paper.
If it is overetched reduce temperature and time if the etching is insufficient do the contrary, just try it out.
Many photoresist developers etch Al2O3 with a very minimal rate (to my experience with TMAH az300mif it was 2-3 nm a minute) if you want a high rate like 2000 nm a minute, then KOH at 80 degrees will do the trick. RIE etching is hard coz you need chlorine or bcl3 and a mask that survives (I only used it for shallow etching)
One can use Cl2 and BCL3 selective plasma with Ti or Si3N4 mask
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