Ion milling process allows to eliminate atomic layers from a sample. In order to know the milling rate, in the same way as sputtering one can fix the power and thus more or less expect a constant milling rate. However I was wondering in case one desires a very precise milling, e.g. just a few atomic layers, a real time milling rate would be more suitable. What are the known (standard) ways to do that experimentally? ie. to meassure milling rate as it occurs.
If you need to etch until the reach of a different layer you can employ dedicate mass spectrometers for endpoint detection.
Ion milling nevertheless is quite linear. You could reduce the ion current to have a very slow rate you calibrate in advance and then maintain a time based process.
Thanks for your answers. However I have an additional question for Marco, do tyou think is possible to control it just by time down to a single monolayer? do you see this viable?@Marco Asa
I know ion milling in a focus ion milling is controlled at real time by directly viewing the sample (with electron miscroscope) but this is clearly much more expensive.
I doubt that the SEM in a dual beam FIB could monitor in real time the etching of a monolayer. Once again it would be matter of precise calibration.
In case of Ion milling if the monolayer is of an element with high cross section with Ar on something else it could be easier to remove it before affecting the underlayer. You can also use a very grazing incidence angle to further reduce ethcing rate and redeposition. It really comes down to the materials involved and the process tolerances.
If you are etching native oxide of Aluminum you can test the Ar milling through electrical measurements. Make Al junctions with differen argon milling time and see when the resistance of the junction drops to small number.
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