Electromigration Damage in Aluminum Film Conductors
01 May 1970-Journal of Applied Physics (American Institute of Physics)-Vol. 41, Iss: 6, pp 2381-2386
TL;DR: In this paper, the flux divergences in large and fine-grained aluminum films were analyzed in terms of the magnitude of vacancy supersaturations at various structural divergence points present in the films studied.
Abstract: Electromigration studies of large‐ and fine‐grain aluminum films showed that fine‐grain films were characterized by a mixed orientation and a grain size of ≈2 μ, and that large‐grain films had a highly preferred 98% 〈111〉 orientation and a grain size of ≈8 μ. Stripes fabricated from the large‐grained films had a consistently longer life, higher activation energy, and lower standard deviation of the life distribution than stripes fabricated from fine‐grained films. These results are interpreted in terms of the nature of flux divergences in the two films. Calculations give the magnitude of vacancy supersaturations at various structural divergences present in the films studied.
Citations
More filters
IBM1
TL;DR: In this article, an overview on the current understanding of electromigration in metals is provided. But the discussion is focused on studies in bulk metals and alloys and not on the studies in metallic thin films.
Abstract: This paper provides an overview on the current understanding of electromigration in metals. The discussion is first focused on studies in bulk metals and alloys. This part includes a thermodynamic formulation of electromigration, a kinetic analysis of the atomic processes and a review of the theory. In addition, experimental results in interstitial and substitutional systems are summarised. The second part of the paper reviews the studies in metallic thin films. This emerged as an important area of electromigration studies since the late 1960s when electromigration damage was found to cause failure of conductor lines in integrated circuits. The discussion will review first the basic nature of electromigration in thin films with emphasis on the role of grain boundaries in mass transport and damage formation. Then the materials issues of electromigration will be explored according to the scaling trends in VLSI technology. Finally, the recent results of electromigration in fine lines and device contacts of dimensions in the micrometre range are discussed.
722 citations
TL;DR: In this article, the electromigration resistance of Al-0.5%Cu meander lines was found to increase with increasing grain size s and degree of {111} preferred orientation and with decreasing spread σ in the grain size distribution.
328 citations
TL;DR: In this paper, a model was constructed for electromigration failure where both Fickian diffusion and mass transport due to the electromigration driving force are considered concurrently and the solution to the resulting diffusion equation yields a current exponent of 2 and an activation energy consistent with grain-boundary self-diffusion.
Abstract: A model was constructed for electromigration failure where both Fickian diffusion and mass transport due to the electromigration driving force are considered concurrently. The solution to the resulting diffusion equation yields a current exponent of 2 and an activation energy consistent with grain‐boundary self‐diffusion. A modification of the standard median time to failure equation first proposed by Black is suggested.
289 citations
TL;DR: The study of dual-damascene Cu has demonstrated the importance of statistics in analyzing EM reliability and has shown statistical evidence of bimodal failure behavior consistent with the presence of a weak and strong failure mode.
Abstract: Electromigration studies on Cu interconnects are reviewed. Some history and more recent results are discussed along with a description of the present interpretations of the active mass transport mechanisms involved in Cu electromigration. The issue of the dual-damascene process and its potential effect on EM reliability is described with special focus on the peculiarities of the dual-damascene interconnect architecture compared to more conventional subtractively etched Al-based interconnects. Experiments performed on dual-damascene interconnects that highlight electromigration reliability issues such as early failure, a tentative explanation for via electromigration failure, and the Blech effect, are summarized. Emphasis is placed on an experimental methodology that uses large interconnect ensembles in a multi-link configuration. Such a large scale study of nearly 10000 interconnects has shown statistical evidence of bimodal failure behavior consistent with the presence of a weak and strong failure mode, which have been identified as voiding, respectively, within the via and the trench at the cathode end of an interconnect. A multi-link approach has also demonstrated a length-dependent distribution of failures that yields a (j/spl middot/L)/sub c/ product value of about 9000 A/cm in dual-damascene Cu/oxide interconnections and is consistent with mass transport that is controlled by the presence of extended defects within Cu such as grain boundaries, interfaces, and/or surfaces. The study of dual-damascene Cu has demonstrated the importance of statistics in analyzing EM reliability.
256 citations
TL;DR: In this article, the authors examined the fundamental physics of electromigration and provided a basis for understanding the factors that affect the lifetimes under the various test conditions, and the care necessary to make fast, wafer-level tests an important process control tool is discussed.
222 citations
References
More filters
TL;DR: In this article, it is shown that positive gradients, in terms of electron flow, of temperature, current density, or ion diffusion coefficient foreshorten conductor life because they present regions where vacancies condense to form voids.
Abstract: Recently, electromigration has been identified as a potential wear-out failure mode for semiconductor devices employing metal film conductors of inadequate cross-sectional area. A brief survey of electromigration indicates that although the effect has been known for several decades, a great deal of the processes involved is still unknown, especially for complex metals and solute ions. Earlier design equations are improved to account for conductor film cross-sectional area as well as film structure, film temperature, and current density. Design curves are presented which permit the construction of high reliability "infinite life" aluminum conductors for specific conditions of maximum current and temperature stress expected in use. It is also shown that positive gradients, in terms of electron flow, of temperature, current density, or ion diffusion coefficient foreshorten conductor life because they present regions where vacancies condense to form voids.
1,267 citations
TL;DR: In this paper, the motion of light transverse scratches, used as markers, has been observed on the surface of gold wires carrying current densities of about 104 A/cm2 for periods of several days.
712 citations
TL;DR: In this article, the process of electromigration in thin Al films was studied directly by transmission electron microscopy during passage of current, and some physical aspects of hole formation, as well as material buildup in the form of hillocks and single crystal Al whiskers, were observed.
Abstract: The process of electromigration in thin Al films was studied directly by transmission electron microscopy during passage of current. Due to electromigration, the Al ions migrate along the test strip from cathode to anode, and the actual opening up of holes near the cathode was observed. The rate of hole formation was used to measure an activation energy. For the test strips, a value of 0.7 eV was obtained. In addition, some physical aspects of hole formation, as well as material buildup in the form of hillocks and single‐crystal Al whiskers, were observed. Some of the whiskers, which were less than 1 μ in diameter, were seen to grow to unusual lengths, occasionally exceeding 50 μ.
174 citations
TL;DR: In this article, two stages of migration were found, the first corresponding to gross mass transport, the second to void growth and stripe failure, and activation energy for the first stage was determined to be 0.5-0.6 eV from change-in-rate, changein-temperature tests, indicating boundary diffusion.
Abstract: Resistance monitoring has been used to follow structural changes during electromigration in aluminum films. Two stages of migration were found, the first corresponding to gross mass transport, the second to void growth and stripe failure. An activation energy for the first stage was determined to be 0.5–0.6 eV from change‐in‐rate, change‐in‐temperature tests, indicating boundary diffusion. Transmission electron microscopy showed voids existing in areas of thinned aluminum. Corollary work on aluminum stripes on NaCl substrates showed nonadhesion to be a strong contributor to void formation, suggesting the possibility that the thinned regions were caused by hot spots at sites of nonadhesion.
145 citations
15 Oct 1967
TL;DR: In this paper, the process of electrotransport in Al thin films was directly observed by transmission electron microscopy, and it was found that hole formation occured in regions where the electron flow was in the direction of increasing temperature.
Abstract: The process of electrotransport in Al thin films was directly observed by transmission electron microscopy As expected, it was seen that hole formation occured in regions where the electron flow was in the direction of increasing temperature Hillocks and whiskers were seen to form where the electron flow was in the direction of decreasing temperature Cine films taken of the process show the holes to grow predominately by a transverse movement of narrow fingers which ultimately coalesce and lead to a catastrophic strip burn out
119 citations