> 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. XeF2 is indeed a gentle (and simple) silicon etch. I measured the etch rate of several materials in XeF2 in a setup in the U.C. Berkeley Microfabrication Laboratory. I found that when etching a whole 4-inch wafer, the ER of silicon varied with location from about 0.1 to 0.3 um/min. Small samples were etched at over 1 um/ min. I found that our approximately stoichiometric silicon nitride was etched at about 12 nm/min, but, curiously, our low-stress, silicon-rich silicon nitride was barely touched, being etched at about 0.2 nm/min. Results will likely vary with deposition conditions and location, so it is advisable to run your own experiment. XeF2 is also readily masked by photoresist. I saw zero etching of two brands of photoresist. Kirt Williams Berkeley Sensor & Actuator Center