How to measure the Al2O3 ultra thin film using ellipsometery. Any one can suggest me a suitable recipe. Al2O3 is deposited on Ge substrate and the estimated thickness will be in the rage of 0.5 - 2nm.
Hello Mohammad,
Are you using a spectroscopic ellipsometer? (would be better than a single wavelength) Here is how I would approach that measurement: (1) characterize well the Ge substrate with the ellipsometer, (2) if possible, characterize Al2O3 with larger thicknesses on Ge first (100nm, 200nm,... to give you an approximation of its index of refraction, which can change for very thin films), (3) measure your Ge with thin Al2O3 and get an estimate of the thickness. I say an 'estimate' because for small thickness values, the index of refraction n and the thickness d become correlated, so that the ellipsometer will be sensitive to small changes of the optical thickness nd, but it will be difficult to get n or d precisely. Good luck!
Better deposit Al2O3 film on one side polished silicon wafer then measure.
Thanks
Cover part of the wafer and deposit your Al2O3 layer. In this way you will make a bare wafer-and Al2O3 layer step Using Michelson Interferometar (you can build easily-see Thin Solid Films) at the step will give you the thickness of the film. Using elipsometer you can determine the index of refraction.
I personally consider this a very difficult question. I will recommend what Samar suggested that you need a very polished Si surface. What makes this most challenging is that, 0.5-2nm lies within the surface roughness of the Si and Ge substrate. This means that native oxide can not be ignored since it may be thicker than the film. The only way to avoid the native oxide is to do vacuum processing.
The other complication arise from that generally below 10 nm film thicknesses, quantum effects can not be ignored and most films are not continuous but rather nucleate into isolated islands, so you may not have a continuous film.
Because of these and many other challenges associated with ultra-thin films, I am not sure SE will give you an accurate thickness. You may need to just characterize the process to determine the growth rate under specific process parameters and estimate the thickness based on the time you need to grow the film.
All the best
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