The influence of alloying interactions on thin film growth stresses

A series of W-Fe and W-Cr thin films were sputter deposited and the intrinsic growth stresses determined by in situ wafer curvature measurements. Under the growth conditions studied, the elemental W film grew in a compressive stress state whereas the elemental Fe and Cr films grew in a tensile stress condition. By mixing Fe or Cr with W, the alloy stress state was bounded between the two elemental stresses which included a zero stress condition. The specific stress response is reported as a function of alloy type that is affected by grain size, grain boundary composition, localized phase separation, and energetic peening effects. Using the ambient temperature deposited zero stress composition, these films were re-deposited at 673K to drive the microstructure towards equilibrium. Under these conditions, both alloys exhibited similar compressive stress states during post-coalescence growth, with the post-deposition stress recovery being greater in the W-Fe film than that of the W-Cr film. This difference was contributed to the dissimilarity in grain sizes between the two films as well as how the solute partitioned in the matrix, i.e. at the grain boundary or as phase separated laths within the grains.