Dear Dr. Sidles,

I would like to suggest using XeF2 as the last release step for the AFM
cantilevers. XeF2 is a gentle vapor-phase etchant that attacks Si at a rate in
the order of 1um/min, depending on the exposed Si area. Using this vapor-phase
etchant, we have released Al structures as thin as 1500A and it could probably
be even thinner. The only question is if XeF2 would attack the SiN. From our
experience, XeF2 may attack certain types of SiN but not others. The easiest
way to find out is to try it out. We have a XeF2 etching system at UCLA if
you'd like to etch.

Regards,
Richard Yeh
UCLA MEMS
> I have two visiting students from Germany who are
> making ultrathin SiN force microscope cantilevers,
> of order 350-800 Angstroms thick and up to 200
> microns long.
>
> The last stage of the process is an anisotropic
> etch in KOH to free the cantilevers from the
> underlying silicon, followed by critical point
> drying in C02.
>
> During the etch, the Si bubbles like crazy,
> to the extend that we are surprised that the
> cantilevers even survive!
>
> Survive they do, however we would like
> to suppress the bubbling if possible.  Can
> anyone offer any suggestions?  We apologize
> if this is a well-know problem with a well
> known solution.... it is only well known
> to those who know it well (which is not us!)
>
> Best wishes from a fan of MEMS ... John Sidles
>
>
>
>