H. Wendrock

Stress evolution during and after sputter deposition of Cu thin films onto Si (100) substrates under various sputtering pressures

The stress evolution during and after dc magnetron sputter deposition of Cu thin films with thicknesses of 20 and 300 nm and deposited with a constant rate of 0.1nm∕s onto Si (100) substrates is studied for various sputtering pressures (0.05–6 Pa). The stress was determined by means of in situ wafer curvature measurements using an optical two-beam deflection method. To correlate the stress evolution with the microstructure development, microstructure investigations were performed by scanning electron microscopy, atomic force microscopy, and electron backscatter diffraction. The results show the transition from tensile to compressive stress with decreasing sputtering pressure at different stages of the deposition. The features of the stress evolution during the early stage of deposition can be ascribed to the Volmer–Weber mechanism. For thicker films, three regions of the sputtering pressure can be distinguished concerning their effect on the stress evolution. The transition from compressive to tensile str...

Microstructural investigation of electrodeposited CuAg-thin films

In this article we present microstructural investigations of electrodeposited CuAg-alloy metallization thin films. The deposition was carried out on Si(100)/SiO2Ta/TaN/Cu-seed substrates at room temperature without any additives. It was found that the mean grain size decreases with increasing dc current density whereas a dependence on the Ag content was not observed. Additionally the crystalline structure and, particularly, the formation of CuAg-solid solutions and grain boundary segregation is discussed on the basis of XRD measurements. The Ag content within a supersaturated copper matrix increases with increasing dc current density.

Transformation-induced plasticity in Fe–Cr–V–C

On the basis of the Fe84.3C4.6Cr4.3Mo4.6V2.2 high-speed tool steel, manufactured under relatively high cooling rates and highly pure conditions, a further improvement of the mechanical characteristics by slight modification of the alloy composition was attempted. For this, the alloy Fe88.9Cr4.3V2.2C4.6 was generated by elimination of Mo. By applying special preparation conditions, a microstructure composed of martensite, retained austenite, and a fine network of special carbides was obtained already in the as-cast state. This material exhibits extremely high compression strength of over 5000 MPa combined with large compression strain of more than 25% due to deformation-induced martensite formation. With this alloy a new composition of transformation-induced plasticityassisted steels was found, which shows an extreme mechanical loading capacity.

In situ stress evolution during sputter deposition of Cu/Co bilayers and multilayers

The stress evolution of Cu∕Co bilayers and multilayers sputtered onto oxidized Si(100) (SiOx) substrates has been studied by in situ substrate curvature measurements with the thickness of the individual layers ranging from 3 to 10 nm. In order to understand the stress developing during deposition, we investigated the microstructure of single layers and bilayers by scanning electron microscopy as well as of the multilayers by cross-section transmission electron microscopy. The growth of Cu and Co on SiOx substrates proceeds by the Volmer-Weber mechanism. Due to the lower mobility, Co layers exhibit a finer grain morphology compared to Cu. The stress evolution and morphology of the first Cu∕Co or Co∕Cu bilayer are still influenced by the SiOx substrates and differ from that of subsequent bilayers. The metal on metal growth of subsequent bilayers is discussed in terms of the surface energies of Cu and Co, respectively. Accordingly, Cu wets Co and Co forms three-dimensional (3D) islands on Cu. After a transit...

In situ stress evolution of Co films sputtered onto oxidized Si (100) substrates

The stress of magnetron-sputtered Co films of thicknesses up to 300 nm has been investigated in a wide range of sputter pressures (0.05-6 Pa) by a laser-based optical bending-beam setup. To correlate the thickness dependence of the stress with changes in the microstructure, the film morphology was investigated by focused ion beam, scanning electron microscopy, and atomic force microscopy. At all of the chosen sputter pressures the film stress is tensile. At low sputter pressures its evolution with film thickness can be related to the Volmer-Weber growth mode of medium-mobility metals and is similar to that of sputtered Cu films concerning nuclei density, island size, and island growth. At higher sputter pressures a transition to columnar grain growth takes place, accompanied by a decrease of the film density and an increase of the electrical resistance. The evolution of stress and microstructure with film thickness is discussed in the context of the stress models proposed in the literature.

Fracture behavior of Mg–Li matrix composites

Abstract Deformation and fracture of Saffil fiber (SF) reinforced Mg, Mg-8 wt.% Li and Mg-12 wt.% Li composites was monitored by means of in-situ scanning electron microscopy during 3-point bend tests. Mg and MgLi matrix composites (10 vol.% SF) were prepared by the melt infiltration technique. Poor interfacial bond causes premature failure of the SF/Mg composite that is usually triggered by the debonding of perpendicular fibers at the convex composite surface. Strong interfaces in SF/Mg12Li composite result in multiple cross-breakage of aligned fibers which is indicative of their participation in the composite strengthening. Resultant composite strengthening is frustrated by massive stress relaxation of the Mg12Li matrix. Strong interfaces and fairly high strength of the Mg8Li matrix cause remarkable strengthening of SF/Mg8Li composites. The cleavage of phases in two-phase Mg8Li matrix plays an insignificant role in the composite failure.

Solidification behaviour of Fe-Gd-Mo alloys

Abstract Microstructures of the solidified Fe–Gd–Mo ternary alloys have been examined using optical and scanning electron microscopy. The nature and chemical composition of the different phases present have been determined by electron probe X-ray microanalysis and X-ray diffraction. These results have been utilized to construct a liquidus projection of the Fe–Gd–Mo system, taking into account the thermal effects detected in the course of solidification with the use of differential thermal analysis. Six ternary peritectic reactions and two ternary eutectic reactions have been found to occur within the liquidus projection. These observations have been used to establish the solidification sequences of the Fe–Gd–Mo alloys studied.

Evidence for cooling‐rate‐dependent icosahedral short‐range order in a Cu–Zr–Al metallic glass

Samples of Cu47.5Zr47.5Al5 metallic glass were prepared at different cooling rate, R. The dependence of the X-ray diffraction patterns on R was analysed by comparing them with corresponding patterns of computer-simulated models generated at different cooling rates as well. The observed changes in the experimental diffraction patterns are reproduced by the simulations, showing an increasing fraction of icosahedral clusters with decreasing cooling rate. The difference of the fractions of icosahedrally coordinated atoms in mould-cast and rapidly quenched Cu47.5Zr47.5Al5 averages to 3 (1)%. Different frozen-in thermal displacements and different density are ruled out as a possible origin for the experimental observations.

A study of the micro- and nanoscale deformation behavior of individual austenitic dendrites in a FeCrMoVC cast alloy using micro- and nanoindentation experiments

Micro- and nanoindentation experiments were conducted to investigate the deformation mechanisms in a Fe79.4Cr13Mo5V1C1.6 (wt. %) cast alloy. This alloy consists of an as cast microstructure mainly composed of austenite, martensite, and a complex carbide network. During microhardness testing, metastable austenite transforms partially into martensite confirmed by electron backscatter diffraction. For nanoindentation tests, two different indenter geometries were applied (Berkovich and cube corner type). Load-displacement curves of nanoindentation in austenitic dendrites depicted pop-ins after transition into plastic deformation for both nanoindenters. Characterizations of the region beneath a nanoindent by transmission electron microscopy revealed a martensitic transformation as an activated deformation mechanism and suggest a correlation with the pop-in phenomena of the load-displacement curves. Furthermore, due to an inhomogeneous chemical composition within the austenitic dendrites, more stabilized region...

Formation of Electromigration Defects in Small Damascene Cu Interconnects with Respect to the Microstructure

Electromigration processes in Cu metallization are of increasing importance in microelectronics. In order to study correlations between microstructural details and localization of electromigration defects generated in narrow electroplated Cu lines, microstructure of entire line was recorded by EBSD measurements with high lateral resolution, and then electromigration test was performed in high vacuum under direct SEM observation. To do this, the lines had to be unpassivated.Short electroplated Cu lines (length of 20 and 50 μm, width of 230 to 130 nm) were loaded at 250°C and 20 MA/cm2 with in‐situ‐SEM observation, and EBSD maps of the line with stepsize, i.e. point distance of 20 nm were acquired before and after test. In the result, a number of hillocks were found to have grown in the vicinity of (100) grains having at least one high angle grain boundary around it. Fatal voids often formed at the cathode end and produced dielectric cracking in some cases. Furthermore, voiding started from the sidewall of ...