A100nm of Chromium is used as a sacrificial layer which is to be removed in order to have a microcantilever suspended. However, after wet etching of Chromium, immersing in DI water, and drying by nitrogen gas, the microcantilever is stuck to the silicon substrate. As a result, nonuniform structures are obtained. I was wondering if there would be a way to get rid of this adhesion?
Radwan Mohammednoor Thank you for your response. I am not pretty sure if I could do this method in our lab or not. I was thinking more about some materials instead of DI water used for rinsing followed by nitrogen drying since our main problem is with DI water surface tension. However, this CO2 dehydration process sounds good and I would like to try it if it is possible for us. Can you please give me some references for how to do this method effectively?
I work with SiNx membranes and putting down metal leads w/ liftoff, so this might not be directly relevant, but a little of an alcohol in the DI, or just using an alcohol like isopropyl or methanol, might help reduce surface tension and likelihood of sticking while drying if you don’t have access to a critical point dryer. I also sonicate when I can—it breaks membranes, so it might not be good for your cantilevers either—but it’s great at keeping particulates off substrates.
Questions from my inexperience with your specifics: Do you know if the cantilevers are sticking while drying or if they possibly aren’t etched completely free by that point? Could they be drooping because they’re too long or thin (z direction)? If so, could a greater standoff from the substrate or a stouter shape help without messing up your experiment?
Sarah Friedensen Thank you for your comment. I tried both IPA and methanol but the adhesion still reminded. With hot IPA some good results achieved, although to reach a stable result there have to be more experiments.
In my case, I tracked the etching process step by step. I found out from the color changing of the SiNx cantilever while etching that all the sacrificial layer was etched away, and then the beam was released. However, going through the rinsing process using DI water and then drying resulted in the sticktion. This sticktion is obviously clear through an optical microscope. About the dimensions of the beam, I would say that it affects the sticktion such that in some papers a critical length is defined for that(Attached you can find an old but useful paper about this sticktion phenomenon). I am reading more about this problem and I would share any new achievement obtained. I would be really grateful if you could share your experience as well.
Article Stiction in surface micromachining
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