ATOMIC-FORCE MICROSCOPY STUDY OF THE SILICON DOPING INFLUENCE ON THE FIRST STAGES OF PLATINUM ELECTROLESS DEPOSITION

The first stages of platinum electroless deposition on (100) Si from h ydrogen fluoride solutions are studied by tapping mode atomic force mi croscopy (AFM), transmission electron microscopy (TEM), and x-ray phot oelectron spectroscopy (XPS). Tapping mode AFM and TEM provide a morph ological characterization of the samples, while XPS accounts for the c ompounds present on the surface. During immersion in an aqueous HF sol ution containing a platinum salt, platinum nucleates on the silicon su bstrate while the surface is etched. The deposited nuclei are polycrys talline, highly pure, and strongly silicidated at room temperature. Me tal deposition takes place by means of a redox reaction in which silic on atoms oxidize, supplying the electrons for the metal to reduce. For all substrates, platinum silicide is formed during deposition at room temperature, suggesting a competition between the deposition of pure metal by an electrochemical mechanism and the formation of the silicid e by direct reaction. For equal deposition times, more platinum deposi ts on p-type substrates than in n(+). p-Type substrates, moreover, und ergo a general increase in roughness in the bare silicon areas, while n-type substrates present a lower and more local etching. This seems t o indicate that electroless platinum deposition is somehow hindered on nt substrates.