Showing papers by "Eduard Arzt published in 1996"

Physical metallurgy of electromigration : Failure mechanisms in miniaturized conductor lines

Abstract: Electromigration (or electrotransport), a classical phenomenon involving the momentum transfer from conduction electrons to atoms at high current densities, has become a major potential threat to the reliability of highly miniaturized metallic conductor lines in advanced microchips. We give an overview of our recent attempts to further, both by experimental observation and by theoretical modelling, the basic understanding of this mechanism which manifests itself in the form of voids and hillocks. It is shown that void nucleation, growth, motion, and shape change must be considered to arrive at a realistic description. The microstructure, especially the grain structure, and the mechanical properties of the conductor line material significantly affect the damage processes, making these investigations a prime example of modern materials science in small dimensions. The improved understanding of the failure mechanisms provides the foundation for a mechanism-based lifetime prediction as well as, eventually, for the rational design of more advanced conductor line alloys.

Plastic Deformation in Thin Copper Films Determined by X-Ray Micro-Tensile Tests

Abstract: Copper is an interesting alternative material for device interconnections in microelectronic circuits because of the lower resistivity and better resistance to electromigration damage in comparison with aluminum. Plastic deformation in thin copper films has been studied at room temperature. Copper films having a thickness of 1 {micro}m were made by sputtering onto nickel substrates with a Si{sub 3}N{sub 4} underlayer and with or without a Si{sub 3}N{sub 4} caplayer. Deformation experiments were conducted using a special micro-tensile tester built into a {theta}-{theta} diffractometer. The problems normally associated with tension tests of free-standing films were avoided by deforming the substrate and film together,. In-situ x-ray measurements of the lattice spacings and lattice spacing distributions were used to determine both elastic and plastic strains. The effects of caplayer and annealing temperature on mechanical properties are reported.

In-Situ Tem Investigation During Thermal Cycling of thin Copper Films

Abstract: In-situ transmission electron microscopy (TEM) was performed to study grain growth and dislocation motion during temperature cycles of Cu films with and without a cap layer. In addition, the substrate curvature method was employed to determine the corresponding stresstemperature curves from room temperature up to 600°C. The results of the in-situ TEM investigations provide insight into the microstructural evolution which occurs during the stress measurements. Grain growth occurred continuously throughout the first heating cycle in both cases. The evolution of dislocation structure observed in TEM supports an explanation of the stress evolution in both capped and uncapped films in terms of dislocation effects.

Dispersion strengthening of disordered and ordered metallic materials : From dislocation mechanisms to new alloys

Abstract: Dispersion strengthening, a classical metallurgical mechanism, has experienced a renaissance over the last decade, both in fundamental understanding and in technical exploitation. Especially its less-understood benefits for high-temperature strength have been an area of concentrated research in our institute for about a decade. In this paper, we summarize, from the perspective of our own contributions to this field, the progress in understanding how dislocations by-pass dispersoids at high temperatures. The resulting improvements in creep strength, for both disordered and order matrix materials, can now be described by mechanism-based constitutive equations. In addition, we have joined efforts with industrial collaborators to develop new dispersion-strengthened alloys based on Ni, Fe, FeAl, Ni 3 Al and NiAl. The resulting materials are also briefly described; some have already become commercial successes, while others exhibit promising property combinations for future applications.

Numerical Simulation of Surface Diffusion Controlled Motion and Shape Change of Electromigration Voids

Abstract: In order to simulate void motion and shape change of electromigration voids a numerical model was developed in which electromigration-driven diffusion on the void surfaces is assumed to act as the primary transport mechanism. The simulation describes the motion and shape evolution of a “two-dimensional void” having a simple initial shape in an isotropic medium. The current density distribution in the vicinity of a void was calculated by the application of a finite element method. Subsequently, the void shape changes by surface diffusion were examined using a finite difference scheme which includes the influence of gradients in curvature along the void surface. The model has been extended to allow other diffusion pathways, such as grain boundaries. The often observed faceting of voids and the formation of slit-like voids are discussed on the basis of simulations in which anisotropic surface tension and anisotropic surface diffusivity were assumed.

Electromigration in Single-Crystal Aluminum Lines Pre-Damaged by Nanoindentation

Abstract: Electromigration tests have been performed on single-crystal Al lines which were pre-damaged by rows of submicrometer-depth indentations made using a nanoindentation device. Indentations were placed close to each other so that their plastic deformation zones overlapped. During subsequent electromigration testing at 280°C and 1 to 2 MA/cm2, no damage was observed in non-indented single-crystal lines, while the indented lines showed electromigration-induced voids at the cathode-side ends of the indented areas, and hillocks at the anode-side ends. The voids grew and moved away from the indentations towards the cathode. The electromigration damage morphology of the indented lines indicates that the mechanical damage generates a local fast diffusion path in the single-crystal lines, which is believed to be due to dislocation core diffusion. A minimum indentation row length was observed, below which no void formed. This electromigration behavior is found to be phenomenologically similar to that of polygranular clusters in near-bamboo lines.

Microstructure and Mechanical Properties of Thin Al-Si-Ge Films

Abstract: The mechanical properties are thought to play an important role in the performance of metallization materials for very large scale integration (VLSI) applications. From recent investigations on bulk materials it is known that Al-Si-Ge alloys can be very efficiently strengthened with only a small amount of the alloying elements. These alloys are potential candidates for future metallizations both because Si and Ge are compatible with the existing semiconductor technology, and because the resistivity is expected to be low. The authors present the first results of detailed characterizations of Al-Si-Ge thin films as a function of sputter conditions and heat treatments. The microstructure was characterized using x-ray diffraction and transmission electron microscopy. The kinetics of precipitation were studied using resistance measurements. Room temperature hardness was investigated using nanoindentation, and the mechanical properties at temperatures up to 240 C were examined using a substrate curvature method. The correlation between precipitate structure and film properties is discussed.

Powder Processing of NiAl for Elevated Temperature Strength

Abstract: In an effort to superimpose two different elevated temperature strengthening mechanisms in NiAl, one lot of an oxide dispersion strengthened (ODS) NiAl powder has been milled in liquid nitrogen (cryomilled) to introduce AlN particles at the grain boundaries, and a second lot of ODS powder was simply roasted in gaseous nitrogen as an alternative means to produce AlN reinforced grain boundaries. Powder from both of these lots as well as the starting material have been consolidated by hot extrusion and tested at 1,300 K. Both nitrogen roasting and cryomilling produced AlN within the ODS NiAl matrix which strengthened the alloy; however, based on the AlN content, cryomilling is more effective.