Papers by Keyword: Metal Thin Films

Abstract: The stress evolution during diffusion annealing of Ni-Cu bilayers (individual layer thicknesses of 50 nm) was investigated employing ex-situ and in-situ X-ray diffraction measurements. Annealing at relatively low homologous temperatures (about 0.3 - 0.4 Tm) for durations up to about 100 hours results in considerable diffusional intermixing, as demonstrated by Auger-electron spectroscopy investigations (in combination with sputter-depth profiling). In addition to thermal stresses due to differences of the coefficients of thermal expansion of layers and substrate, tensile stress con-tributions in the sublayers arise during the diffusion anneals. The obtained stress data have been discussed in terms of possible mechanisms of stress generation. The influence of diffusion on stress development in the sublayers of the diffusion couple during heating and isothermal annealing was investigated by comparing stress changes in the bilayer system with corresponding results obtained under identical conditions for single layers of the components in the bilayer system. The specific residual stresses that emerge due to diffusion between the (sub)layers in the bilayer could thereby be identified.

Abstract: After a brief discussion of possible mechanisms of stress generation in thin film diffusion/reaction couples, two recent experimental examples are reviewed: (i) Thin film diffusion couples (Pd-Cu, individual layer thicknesses: 50nm) prepared by DC-magnetron sputtering on silicon substrates. The microstructural development, phase formation and the stress evolution during diffusion annealing have been investigated employing Auger-electron spectroscopy in combination with sputter depth profiling, transmission electron microscopy, in-situ wafer-curvature measurements and ex-situ and, in particular, in-situ X-ray diffraction measurements. (ii) Tin layers on copper substrates (layer thicknesses of some microns) prepared by electrodeposition. Upon storage at ambient temperatures, Cu diffuses into the Sn layer and forms the intermetallic phase η’- Cu6Sn5. The phase formation is accompanied by a volume expansion and as a consequence, compressive residual stresses can be generated in the Sn layers. These compressive residual stresses may drive the formation of Sn whiskers on the Sn surface. The microstructural development, phase formation and the stress evolution during diffusion annealing have been investigated employing scanning electron and focused ion beam microscopy, metallography and ex-situ and, in particular, in-situ X-ray diffraction measurements.

Abstract: Thin film diffusion couples (Pd-Cu, individual layer thicknesses: 50 nm) have been prepared by DC-magnetron sputtering on silicon substrates coated with amorphous inter-layers (Si3N4 on top of SiO2). The microstructural development, phase formation and the stress evolution during diffusion annealing have been investigated employing Auger-electron spectroscopy in combination with sputter depth profiling, ex-situ and, in particular, in-situ X-ray diffraction measurements. Upon annealing at relatively low temperatures (175°C to 250°C) for durations up to 100 hours, considerable diffusional intermixing occurs. Interdiffusion is accompanied by the sequential formation of a new phase (Cu3Pd). The detected stress changes are discussed in terms of possible mechanisms of stress generation.

Abstract: The pattern formation during delamination and buckling in sputter-deposited tungsten thin films under large compressive stresses was investigated. The films were analyzed in situ by a cantilever beam technique, and ex situ by atomic force microscopy (AFM) and focused ion beam. Depending on the magnitude of compressive strain in thin films, different types of buckling patterns were observed. For stresses above a critical value, there was a regime of steady growth in which the incipient blister evolves into a regular sinusoidal-like propagation. At higher strains, the sinusoidallike wrinkles were developed with constant widths and wavelengths. Some of the wrinkles bifurcated to form branches. With further increase in stress the complicated buckling patches were formed with many irregular lobes. These types of pattern formation have been supported by elastic energy calculations.