# What favors island growth of a sputtered material?

What would be the best choice of parameters in general if one would like to get pure island growth (i.e. Volmer-Weber growth) in a sputtering deposition process and what would be a good estimate of the maximum height of these islands (e.g. 10 nm) before they will form a continuous film?

By parameters I mean the temperature of the substrate, the argon ion pressure and the applied voltage. If you can think of anything else that could be changed, please add.

Also, how do these parameters depend on the material? I can't find good references for different materials online, just a few special cases such as silver or gold islands on a sapphire substrate. Can one make a general statement about different lattices and defects in a substrate, e.g. a cleaved surface that basically provides no nucleation sites except step edges, which unfortunately won't lead to islands but to "lines" along these edges.

A sketch of the sputtering process :

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The wetting behavior is basically defined through the surface and interface energies. A material A will wet material B if:

$$E_{surf}(A) + E_{int}(AB) < E_{surf}(B)$$

The surface of material B is minimized by wetting material A (and therefore leading to layer-by-layer growth. The reverse case leads to island formation, namely if:

$$E_{surf}(B) + E_{int}(AB) < E_{surf}(A)$$

So, this all in all does not really depend on the growth conditions or process. This is e.g. discussed in "Epitaxy of Dissimilar Materials" by C. Palmstrom

From a more practical perspective: You can try to modify the interface energy by various things: E.g. think about off-cut wafers, where you have a lot of surface steps present or even wafers with a different orientation, if this is an option. Further things to be changed or considered are surface defects, adhesion agents, e.g. sputtering of a thin film, to create a surface, which will favor island growth (may or may not be an option), and so on.

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You may also find that you don't get good adhesion if conditions favor islands. If sputtered atoms stick to each other better than they stick to the substrate ... – mmesser314 Jul 28 '15 at 12:26