Hi Brian, thanks for suggestion about spectroscopic reflectometer. About stylus profilometer, i have a Veeco optical profilometer. In principle i may use this tool to measure wafer thickness. But how can i be sure that there will be not a small dust particle between the wafer and the chuck where the wafer lean on ? This would alter the real wafer thickness value. Thanks, Andrea > Hi Andrea, > > If you have access to a spectroscopic reflectometer, you should be able to > use it to measure the thickness of your membranes. You should check with > the manufacturer of the tool to see if your membranes fall within the > thickness range accessible to the tool and how to configure the software > film stack model. I haven't tried this myself, but I know of at least one > manufacturer that advertises this as a capability of their product. > > Another option is to use a stylus profilometer to measure the etch depth, > and subtract this from the thickness of the wafer. The accuracy of this > measurement should be more dependent on the thickness tolerance of your > wafer than the accuracy of the profilometer itself (which is usually > around > +/- 10nm). > > Good luck, > > Brian Stahl