Influence of substrate properties and annealing temperature on the stress state of magnetron sputtered tungsten thin films

The influence of substrate properties and annealing temperature on the stress state of tungsten thin films deposited by dc reactive magnetron sputtering was studied using 310 steel (AISI), Fecralloy (R) and Invare substrates. Besides elemental tungsten, only residual amounts of contamination elements (O, C, Ar, etc.) were detected by electron probe microanalysis. Only the alpha-W crystalline structure, with a preferential < 110 > orientation, was detected in all the films by x-ray diffraction. The highest lattice parameters were measured for the films deposited on 3.10 steel substrates, while the smallest values were obtained for the films deposited on Invar (R) substrates. These results are closely related to the thermal expansion coefficients of the substrates. All the as-deposited films were in a compressive stress state independent of the substrate type (-3 GPa for 310 steel and Fecralloy (R) substrates and -2 GPa for Invar (R) substrates). The residual compressive stresses of the films deposited on Fecralloy (R) substrates strongly decrease with annealing temperatures up to approximate to-8 GPa at 1175 K. This result shows that the measured compressive stresses are not real, and they are a direct consequence of plastic deformation of the substrate. On the contrary, the compressive stresses measured in the films deposited on Invar and 310 steel substrates are real as plastic deformation of the substrates is not observed. (c) 2006 American Vacuum Society.