Correlation between the surface roughness value and the value of the grain size of the thin layers
Are you take into a mind the structured films or layers filled by particles (granules) made of another material? In first case the roughness depends on peculiarities of film structure (characteristic size of structural unit (cell)).
If we consider the solid layers where each foreign granule is capsulated by film material without discontinuities, the roughness will be determined by average size of granule and thickness of capsulating material.
Generally, as the grain size increases, the roughness increases.
Apart from this, it also depends on the size of the granule, shape of the granule and how the granules are packed.
It also depends on how you are measuring the roughness i.e., what type of probe (dimensions) or technique you are using for measuring surface roughness.
I measured the roughness by atomic force microscopy using XE-100 instrument (Park Systems Corporation) in non-contact mode (NC-AFM).
Most often, probably, the roughness increases with increasing grain size. But for films of a particular composition and not a composite type, different cases can occur depending on the type of material, method and conditions for deposition of the material (from melt, solution or the gas phase, the choice of substrate type, deposition temperature, and possibly chemical reactions during coprecipitation). The rough surfaces have more nucleation sites, therefore more grains (crystallites) will appear. Further, there are different cases. These can be many small grains with different orientation of crystallographic axes. Original roughness can have grasses, grains can collide and coalesce, forming a continuous or discontinuous (island) film. So, the roughness may be different depending not only on size but also on the shape and orientation of grains. The roughness may depend not only on size but also on the shape and orientation of grains.
It is desirable to explore the film also by alternative methods (for different types of films and grain sizes they can be different, but you can try scanning and/or optical microscopy, and in some cases x-ray diffraction, electronography, etc.).
The surface roughness can be defined in various ways and, accordingly, this term has a different meaning. Depending on which parameters of the relief are used to assess the roughness, you can get a different description of the situation. Therefore, it is difficult to associate unambiguously the grain size and the roughness. The problem also depends on what kind of film we have in mind, because in different conditions from the same composition there can be obtained relatively smooth films of all varieties: amorphous, polycrystalline or consisting of amorphous and polycrystalline phases. Moreover, in a narrow transition temperature region are formed of a film having substantial surface roughness. The problem of the analysis of the roughness of silicon films examines in detail in the publication [A. V. Novak, Novak V. R. ROUGHNESS OF AMORPHOUS, POLYCRYSTALLINE AND HEMISPHERICAL-GRAINED SILICON FILMS \ Technical Physics Letters. 2013. V. 39(10) P.858-861]
See laso their article The evolution of surface morphology during the growth of poly-Si films with hemispherical grains in Technical Physics Letters. 2014. V. 40.
The authors of article "The evolution of surface morphology during the growth of poly-Si films with hemispherical grains" note that with increasing film thickness from 30 to 160 nm, the grain size increases from 64 to 170 nm. The value of the roughness has the same value (0.92 ± 0.03) for all films. The obtained value coincides with the data for the LPCVD films of amorphous and polycrystalline silicon (0.92 ± 0.03) and is close to the value for amorphous silicon films obtained by thermal evaporation (0.9 ± 0.02).
Dear Alexander T. Morchenko
From your answer, I couldn't decide if there is a relation between film thickness and roughness. Actually I was searching through google about the relation between film thickness and roughness, and see this question and read all your comments which are very interesting. Can you answer me please on my question "Is there a relation between thin film thickness and roughness?"
Many thanks in advance with regards
Fayroz
To Fayroz A Sabah
I have not experience with various types of films. And there is no definite answer to this question. A lot depends on the film material and the substrate, surface state and crystallographic orientation of the substrate, the film type and the method of its deposition (epitaxial monocrystalline or polycrystalline, growth from gas phase or liquid phase, from solution or from the melt, spraying, evaporation, graphoepitaxy, etc.). If the thin film on a rough substrate, the roughness will manifest itself soon. For thicker layers, can occur healing irregularities.
Dear Dr. Kraini Mabrouk
Have a nice day
the appended files may help you
Good luck
Dear Dr. Ahmed Saeed Hassanien
Have a nice day.
Thanks for the 2 articles, they are full of information.
Best regards
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