Microstructure and surface morphology of cryogenic processed thin metal films studied by atomic force microscope

Thin metal films of Au and Al were deposited by thermal evaporation at a substrate temperature of 77 K [low temperature (LT)]. For comparison purposes, the same films were also prepared with the substrates at room temperature (RT) of 300 K. The surface morphology and microstructure of these films were studied by atomic force microscope. The film thicknesses used were 100 and 200 Å. At a thickness of 100 Å, the LT Au film consisted of smaller-sized grains showing smoother surface morphology, whereas the RT Au film appeared to have a rougher surface. At a thickness of 200 Å, the LT Au film showed much larger-sized grains. The 200 Å RT Au film showed surface morphology similar to that of the 100 Å RT Au film. For Al films, the 100 Å film showed smaller-sized grains for both LT and RT depositions. As the thickness increased, the 200 Å Al LT film showed much larger-sized grains, similar to that of the 200 Å Au LT film. Since the larger-sized grains were observed in both 200 Å Au and Al LT films, less surface scattering was expected which resulted in the low resistivity in the LT films.