Effect of “bamboo” grain boundaries on the maximum electromigration-induced stress in microelectronic interconnect lines

1998 ◽  
Vol 83 (7) ◽  
pp. 3595-3599 ◽  
Author(s):  
R. J. Gleixner ◽  
W. D. Nix
Keyword(s):  
Grain Boundaries ◽  
Induced Stress ◽  
Interconnect Lines

An Examination of Mass Transport Paths in Conventional and Highly Textured AL-CU Interconnect Lines

1997 ◽  
Vol 472 ◽  
Author(s):  
R. J. Gleixner ◽  
H. Kanekof ◽  
M. Matsuot ◽  
H. Toyodat ◽  
W. D. Nix
Keyword(s):  
Mass Transport ◽  
Grain Boundaries ◽  
Line Width ◽  
Void Growth ◽  
Strong Dependence ◽  
Surprising Result ◽  
Cu Interconnect ◽  
Voids Growth ◽  
Interconnect Lines

ABSTRACTThe electromigration lifetime of aluminum interconnect lines shows a strong dependence on the quality of the texture in the metal. This observation has been explained in terms of a decreased diffusivity along the grain boundaries, generally the dominant path for diffusion and void growth. As the texture in the metal is strengthened, atomic order along the grain boundaries is increased, and diffusion is suppressed.In this paper, we examine passivated A1–0.5wt%Cu interconnect lines having either TaAl underlayers or conventional Ti/TiN underlayers. Rocking curve measurements confirm that Al deposited on TaAl has a very strong (111) texture (FWHM ∼ 0.6°) compared to Al on Ti/TiN (FWHM ∼ 6°). Interconnect lines of both types were electrically stressed at 225°C and 250°C for 20 hours at a current density of 3 MA/cm2. The lines were then stripped of passivation, and the void numbers, sizes, and morphologies were determined.Analysis of the void data gave a surprising result: the void volume in the highly-textured Al was greater than in the conventional Al. However, voids in the conventional Al were observed to follow grain boundaries across the width and sever the line, while such destructive void growth was not observed in the highly-textured Al. Instead, voids grew either with a faceted shape or along the line edge, never extending across the line width. Modeling electromigration in the surrounding microstructures shows that void locations in the highly-textured lines are often independent of the surrounding grain boundaries. In this case, the line sidewalls appear to be significant mass transport paths. Since these paths do not cross the line width, voids growth across the line is difficult. This resistance to fatal damage makes highly textured aluminum a promising interconnect material.

Modeling Electromigration-Induced Stress Buildup Due to Nonuniform Temperature

1994 ◽  
Vol 338 ◽  
Author(s):  
J. J. Clement ◽  
C. V. Thompson ◽  
A. Enver
Keyword(s):  
Integrated Circuits ◽  
Driving Force ◽  
Stress Evolution ◽  
Nonuniform Temperature ◽  
Flux Divergence ◽  
Atomic Transport ◽  
Atomic Flux ◽  
Induced Stress ◽  
Interconnect Lines ◽  
Stress Buildup

ABSTRACTAtomic transport due to electromigration in interconnect lines in integrated circuits depends strongly on temperature. Therefore temperature nonuniformities can create sites of atomic flux divergence resulting in material accumulation or depletion leading to failure. The mechanical stress which will evolve at the sites of material flux divergence will oppose the electromigration driving force. A model is developed to describe the stress evolution during electromigration in the presence of temperature nonuniformnities. Solutions of the differential equations describing the electromigration-induced stress buildup are calculated numerically. The solutions are compared to experimental data in the literature.

An Examination of Mass Transport Paths in Conventional and Highly Textured Al-Cu Interconnect Lines

1997 ◽  
Vol 473 ◽  
Author(s):  
R. J. Gleixner ◽  
H. Kanekot ◽  
M. Matsuo ◽  
H. Toyoda ◽  
W. D. Nix
Keyword(s):  
Mass Transport ◽  
Grain Boundaries ◽  
Line Width ◽  
Void Growth ◽  
Strong Dependence ◽  
Surprising Result ◽  
Cu Interconnect ◽  
Voids Growth ◽  
Interconnect Lines

ABSTRACTThe electromigration lifetime of aluminum interconnect lines shows a strong dependence on the quality of the texture in the metal. This observation has been explained in terms of a decreased diffusivity along the grain boundaries, generally the dominant path for diffusion and void growth. As the texture in the metal is strengthened, atomic order along the grain boundaries is increased, and diffusion is suppressed.In this paper, we examine passivated Al-0.5wt%Cu interconnect lines having either Ta Al underlayers or conventional Ti/TiN underlayers. Rocking curve measurements confirm that Al deposited on TaAl has a very strong (111) texture (FWHM ∼ 0.6°) compared to Al on Ti/TiN (FWHM ∼ 6°). Interconnect lines of both types were electrically stressed at 225°C and 250°C for 20 hours at a current density of 3 MA/cm2. The lines were then stripped of passivation, and the void numbers, sizes, and morphologies were determined.Analysis of the void data gave a surprising result: the void volume in the highly-textured Al was greater than in the conventional Al. However, voids in the conventional Al were observed to follow grain boundaries across the width and sever the line, while such destructive void growth was not observed in the highly-textured Al. Instead, voids grew either with a faceted shape or along the line edge, never extending across the line width. Modeling electromigration in the surrounding microstructures shows that void locations in the highly-textured lines are often independent of the surrounding grain boundaries. In this case, the line sidewalls appear to be significant mass transport paths. Since these paths do not cross the line width, voids growth across the line is difficult. This resistance to fatal damage makes highly textured aluminum a promising interconnect material.

The Effect of Cluster Interactions on Electromigration Induced Stress Evolution in Confined Metal Lines

1995 ◽  
Vol 391 ◽  
Author(s):  
D.D. Brown ◽  
J.E. Sanchez ◽  
P.R. Besser ◽  
M.A. Korhonen ◽  
C.-Y. Li
Keyword(s):  
Integrated Circuits ◽  
Grain Boundaries ◽  
Length Distribution ◽  
Diffusion Path ◽  
Line Length ◽  
Segment Length ◽  
Stress Profile ◽  
Fast Diffusion ◽  
Metal Interconnects ◽  
Interconnect Lines

AbstractIn near-bamboo interconnect lines used in advanced integrated circuits, electromigration flux divergences occur at the intersection between polycrystalline cluster segments (where grain boundaries offer a fast diffusion path), and bamboo segments (where there are no grain boundaries along the line length). For confined, passivated metal interconnects, these flux divergences are linked to the evolution of significant mechanical stresses in the metal. A quasisteady state stress distribution builds up relatively quickly in the cluster segments and remains unchanged until there is significant diffusion into the bamboo segments. The stress profile of a given cluster then becomes dependent on neighboring clusters as well as the diffusivity and flux in the separating bamboo segments. Previous analyses of electromigration failure in interconnect lines have focused on the distribution of cluster lengths and the stress build up in isolated cluster segments. In this paper, we show that the bamboo length distribution can strongly affect the interaction between clusters and the evolution of stresses in a near-bamboo interconnect during electromigration. We present simulation results, using a ratio of cluster to bamboo diffusivity Dc/Db=100, which show greater interactions and larger maximum stresses in cluster segments as the average bamboo segment length decreases and as the bamboo segment length distribution widens.

Comparison of Line Stress Predictions with Measured Electromigration Failure Times

2005 ◽  
Vol 863 ◽  
Author(s):  
Rao R. Morusupalli ◽  
William D. Nix ◽  
Jamshed R. Patel ◽  
Arief S. Budiman
Keyword(s):  
Void Formation ◽  
Atomic Diffusion ◽  
Time To Failure ◽  
Stress Evolution ◽  
Failure Times ◽  
Induced Stress ◽  
Product Lifetime ◽  
Metal Interconnects ◽  
Interconnect Lines ◽  
Pure Cu

AbstractReliability of today's interconnect lines in microelectronic devices is critical to product lifetime. The metal interconnects are carriers of large current densities and mechanical stresses, which can cause void formation or metal extrusion into the passivation leading to failure. The modeling and simulation of stress evolution caused by electromigration in interconnect lines and vias can provide a means for predicting the time to failure of the device. A tool was developed using MathCAD for simulation of electromigration-induced stress in VLSI interconnect structures using a model of electromigration induced stress. This model solves the equations governing atomic diffusion and stress evolution in one dimension. A numerical solution scheme has been implemented to calculate the atomic fluxes and the evolution of mechanical stress in interconnects. The effects of line geometries and overhangs, material properties and electromigration stress conditions have been included in the simulation. The tool has been used to simulate electromigration-induced stress in pure Cu interconnects and a comparison of line stress predictions with measured electromigration failure times is studied. Two basic limiting cases were studied to place some bounds on the results. For a lower bound estimate of the stress it was assumed that the interface can be treated like a grain boundary in Cu. For an upper bound estimate it was assumed that the interface can be treated like a free surface of Cu. Existing data from experimental samples with known structure geometries and electromigration failure times were used to compare the electromigration failure times with predicted stress build-up in the interconnect lines.

In-Situ Electromigration Damage of Al Interconnect Lines and the Influence of Grain Orientation

1999 ◽  
Vol 563 ◽  
Author(s):  
A. Buerke ◽  
H. Wendrock ◽  
T. KÖtter ◽  
S. Menzel ◽  
K. Wetzig ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Grain Orientation ◽  
Local Orientation ◽  
Boundary Map ◽  
Diffusion Paths ◽  
Bamboo Structure ◽  
Ebsd Technique ◽  
Interconnect Lines ◽  
Current Loading

AbstractIn this work the authors want to report some experiments concerning unpassivated Al interconnect lines of 8 and 1.4 microns width which have been damaged by in-situ electromigration in the SEM (temperature 230°C, current density 2 and 4×106 A/cm2, respectively). The wider line represents a polygrained structure with few blocking grains spanning the whole width, whereas the narrow line shows bamboo structure. Before electromigration, the local orientation and thus the position of all grain boundaries was mapped by EBSD technique along the entire interconnect line. During and after in-situ current loading in the SEM, the damaged sites were correlated with the grain boundary map to locate where the diffusion paths are situated most likely. It was found that not the deviation from <111> fibre texture, but the misorientation class of the grain boundaries is essential for the localization of the fatal defects.

Morphology, Distribution and Identification of Micro-Constituents Along Grain Boundaries in Nickel-Base Alloys

1973 ◽  
Vol 31 ◽  
pp. 176-177
Author(s):  
D. E. Fornwalt ◽  
A. R. Geary ◽  
B. H. Kear
Keyword(s):  
Electron Microscope ◽  
Grain Boundaries ◽  
Volume Fraction ◽  
Rupture Life ◽  
Stress Rupture ◽  
High Volume ◽  
Precipitate Morphology ◽  
Stress Rupture Life ◽  
Nickel Base ◽  
Scanning Electron

A systematic study has been made of the effects of various heat treatments on the microstructures of several experimental high volume fraction γ’ precipitation hardened nickel-base alloys, after doping with ∼2 w/o Hf so as to improve the stress rupture life and ductility. The most significant microstructural chan§e brought about by prolonged aging at temperatures in the range 1600°-1900°F was the decoration of grain boundaries with precipitate particles.Precipitation along the grain boundaries was first detected by optical microscopy, but it was necessary to use the scanning electron microscope to reveal the details of the precipitate morphology. Figure 1(a) shows the grain boundary precipitates in relief, after partial dissolution of the surrounding γ + γ’ matrix.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

The Effect of Specimen Thickness and Probe Size on Aem Analysis of Cr-Depletion Profiles in Sensitized Stainless Steel

1982 ◽  
Vol 40 ◽  
pp. 518-519
Author(s):  
E. L. Hall
Keyword(s):  
Grain Boundaries ◽  
Boundary Region ◽  
Chromium Concentration ◽  
Foil Thickness ◽  
Specimen Thickness ◽  
Probe Size ◽  
Analytical Electron ◽  
Analytical Electron Microscope ◽  
Sensitization Process ◽  
Compositional Gradients

Sensitization in stainless steels is caused by the formation of chromium-rich M23C6 carbides at grain boundaries, which depletes the adjacent matrix and boundary region of chromium, and hence leads to rapid intergranular attack. To fully understand the sensitization process, and to test the accuracy of theories proposed to model this process, it is necessary to obtain very accurate measurements of the chromium concentration at grain boundaries in sensitized specimens. Quantitative X-ray spectroscopy in the analytical electron microscope (AEM) enables the chromium concentration profile across these boundaries to be studied directly; however, it has been shown that a strong effect of foil thickness and electron probe size may be present in the analysis of rapidly-changing compositional gradients. The goal of this work is to examine these effects.

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