The role of tin in the formation of micro- and nano-structured surfaces of layered Si-Sn-Si films

The methods of Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and X-ray fluorescence microanalysis are used to study the influence of tin on the shape and sizes of micro- and nano-structures arising on the surface of layered Si–Sn–Si films, as well as on the formation of Si nanocrystals in them during the tin-induced crystallization of amorphous silicon. In this work, the problems dealing with the experimental evaluation of the formation efficiency of Si nanocrystals in Si–Sn–Si films, the determination of the forms and scales of the film surface roughness, and the micro-distribution of impurities over the film surface and across the film thickness are tackled. The possibility of the formation of Si nanocrystals a few nanometers in size over most of the Si–Sn–Si film volume is experimentally confirmed. It is established for the first time that, during the production of such films using the thermal vacuum sputtering method, the thickness of a tin layer and its ratio to the thickness of silicon layers determine the shape and scale of the periodic surface relief structuring, which is important for the production of electronic devices. Quasi-spherical formations from 20 nm to 2–3 μm in diameter turned out to be the main element of the film surface relief structuring. The surface roughness induced by them can vary from a few nanometers to several tens of nanometers, depending on the layer deposition conditions. The shape of surface formations can change from cluster-like dendrites of the fractal type to convex ellipsoids and polygons. It is shown that the primary structuring occurs as the formation of a layer of hemispherical tin microdroplets already in the course of tin deposition. The secondary structuring occurs at the stage, when the second layer of silicon is deposited onto the layer of tin hemispheres. At this stage, a layer of the amorphous semiconductor is formed on the surface of the liquid metal, and this phenomenon is studied for the first time. The so-obtained amorphous silicon has a porous structure and consists of cluster-like dendrites of the fractal type about hundreds of nanometers in scale. The smallest dendrite elements also have a quasi-spherical shape 20–50 nm in diameter. Possible applications of the obtained results are discussed. (author)