Effect of substrate temperature on the microstructure of thin niobium films

Abstract

Niobium films with constant thickness have been deposited on sapphire (11 20) by electron-beam evaporation at different substrate temperatures (150 ° C ⩽ T S ⩽ 750 ° C). The samples were characterized by X-ray diffraction and resistivity measurements. X-ray reflectivity shows that all films are covered with an oxide layer of about 20 Å in ambient atmosphere. The (110) texture at high T S decreases towards lower T S, accompanied by an increasing surface roughness. Below T S = 350 °C the grain size in the growth direction becomes smaller than the film thickness and a relaxation of intrinsic stress is observed. A transition from a columnar growth structure to a fine grained microstructure is inferred. The change of the microstructure with T S is probably due to the temperature dependent grain boundary mobility during the deposition process.