Stress in sputter-deposited Cr films: Influence of Ar pressure

We studied the tensile stress and grain-width evolution in sputter-deposited Cr films with thickness from 20?nm to 2.7??m. Films were deposited in an industrial Hauzer 750 physical vapor deposition machine at 50–80?°C. The films exhibited a columnar microstructure. A power law behavior of the tensile stress as well as of the average grain width with thickness was observed. Both power exponents were strongly dependent on the Ar pressure during deposition. The power exponent ? for stress varied from 0.26 to 0.79 for the range of Ar pressures used (5×10?3–2×10?2?mbar). The mechanism of tensile stress generation is the shrinkage of the grain boundaries. Assuming the same shrinkage of the grain boundaries all through the layer, the stress and the grain width would be inversely proportional. Indeed, the grain width followed the same power law as the stress at low Ar pressure [? = 0.3(1)], but not at high Ar pressure [? = 0.58(3)]. Transmission electron microscopy showed the formation of numerous voids. At higher Ar pressure the void fraction is significantly higher than at low pressure, thereby diminishing stress generation.Kavli Institute of NanoscienceApplied Science