Electromigration in thin aluminum films on titanium nitride
TL;DR: In this paper, the aluminum electromigration drift velocity was measured at the temperature range 250-400°C and an activation energy of 0.65 eV was found for the drift velocity, which was explained by opposing chemical gradients created by the atom pile-up and depletion at the stripe ends.
Abstract: The aluminum electromigration drift velocity was measured at the temperature range 250–400 °C. A threshold current density was found inversely proportional to the stripe length. An activation energy of 0.65 eV was found for the drift velocity. The occurrence of the threshold is explained by opposing chemical gradients created by the atom pile‐up and depletion at the stripe ends. The threshold may explain several observations reported previously. The threshold is increased by decreasing the temperature or by enclosing the aluminum in silicon nitride. Virtually no electromigration is seen for very short aluminum stripes even at current densities above 106 A/cm2.
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02 Feb 2004TL;DR: The role of stress in mass transport is discussed in this article, where the authors consider anisotropic and patterned films, buckling, bulging, peeling and fracture.
Abstract: 1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.
1,562 citations
Cites background or methods from "Electromigration in thin aluminum f..."
...estimating thin ̄lm stress, particularly for ̄lms deposited on Si wafers used in microelectronics, involves the re°ection of a laser beam from the substrate; this technique is often simply referred to as the wafer curvature measurement method, and it has been discussed by Retajczyk and Sinha (1980), Pan and Blech (1984), Flinn et al. (1987), Volkert (1991), and Schull and Spaepen (1996), among others....
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...The existence of this threshold length for onset of electromigration damage was ̄rst recognized by Blech (1976), and evidence for its existence is noted in the discussion of the drift test in Section 9....
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...Loss of current carrying capability and the possible occurrence of electrical short-circuits due to electromigration are major concerns of practical interest which can limit the reliability of integrated circuits (D'Heurle (1971), Blech (1976), Suo (2003))....
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...The radius of curvature of the substrate is then the radial distance between the two locations on surface at which the di®raction measurements are made divided by the di®erence in the angular position of the intensity maxima (Blech and Meieran (1967); Van Mellaert and Schwuttke (1972); Blech and Cohen (1982))....
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...estimating thin ̄lm stress, particularly for ̄lms deposited on Si wafers used in microelectronics, involves the re°ection of a laser beam from the substrate; this technique is often simply referred to as the wafer curvature measurement method, and it has been discussed by Retajczyk and Sinha (1980), Pan and Blech (1984), Flinn et al....
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Patent•
01 Aug 2008
TL;DR: In this article, the oxide semiconductor film has at least a crystallized region in a channel region, which is defined as a region of interest (ROI) for a semiconductor device.
Abstract: An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.
1,501 citations
TL;DR: In this paper, the authors used the format of case study to review six reliability problems of Pb-free solders in electronic packaging technology and conducted analysis of these cases on the basis of thermodynamic driving force, time-dependent kinetic processes, and morphology and microstructure changes.
Abstract: Solder is widely used to connect chips to their packaging substrates in flip chip technology as well as in surface mount technology. At present, the electronic packaging industry is actively searching for Pb-free solders due to environmental concern of Pb-based solders. Concerning the reliability of Pb-free solders, some electronic companies are reluctant to adopt them into their high-end products. Hence, a review of the reliability behavior of Pb-free solders is timely. We use the format of “case study” to review six reliability problems of Pb-free solders in electronic packaging technology. We conducted analysis of these cases on the basis of thermodynamic driving force, time-dependent kinetic processes, and morphology and microstructure changes. We made a direct comparison to the similar problem in SnPb solder whenever it is available. Specifically, we reviewed: (1) interfacial reactions between Pb-free solder and thick metalliztion of bond-pad on the substrate-side, (2) interfacial reactions between Pb-free solder and thin-film under-bump metallization on the chip-side, (3) the growth of a layered intermetallic compound (IMC) by ripening in solid state aging of solder joints, (4) a long range interaction between chip-side and substrate-side metallizations across a solder joint, (5) electromigration in flip chip solder joints, and finally (6) Sn whisker growth on Pb-free finish on Cu leadframe. Perhaps, these cases may serve as helpful references to the understanding of other reliability behaviors of Pb-free solders.
1,315 citations
TL;DR: In this paper, the authors reviewed what is current with respect to electromigration in Cu in terms of resistance, capacitance delay, electromigration resistance, and cost of production, and concluded that the most serious and persistent reliability problem in interconnect metallization is electromigration.
Abstract: Today, the price of building a factory to produce submicron size electronic devices on 300 mm Si wafers is over billions of dollars. In processing a 300 mm Si wafer, over half of the production cost comes from fabricating the very-large-scale-integration of the interconnect metallization. The most serious and persistent reliability problem in interconnect metallization is electromigration. In the past 40 years, the microelectronic industry has used Al as the on-chip conductor. Due to miniaturization, however, a better conductor is needed in terms of resistance–capacitance delay, electromigration resistance, and cost of production. The industry has turned to Cu as the on-chip conductor, so the question of electromigration in Cu metallization must be examined. On the basis of what we have learned from the use of Al in devices, we review here what is current with respect to electromigration in Cu. In addition, the system of interconnects on an advanced device includes flip chip solder joints, which now tend ...
885 citations
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
References
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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, the drift velocities per unit current density ranged between 10-13 and 10-15 cm3 A-1 s-1 and the gold motion was always in the direction of electron flow.
162 citations
IBM1
TL;DR: In this article, some fundamental aspects of electromigration phenomena as they have been studied in "bulk" metallic conductors are reviewed, and practical guidelines for the design of thin-film interconnections, and for the interpretation of accelerated test data are given.
Abstract: Some fundamental aspects of electromigration phenomena as they have been studied in "bulk" metallic conductors are reviewed. In an electric field atoms are subjected to a force due to the field, and to a force which results from the motion of electrical carriers, electrons, or holes. In bulk samples, and at high temperatures, these forces cause the displacement of atoms by a lattice mechanism which is also responsible for the diffusion of atoms in a concentration gradient. In thin films, electromigration has been found to occur at lower temperatures (and higher current densities) by a grain boundary diffusion mechanism. Electromigration may cause failures at material discontinuities, such as found at terminals, at temperature gradients, or at structural inhomogeneities. The process of crack formation, as observed in aluminum thin films, is described. Failure times are a function of the activation energy for diffusion and of exponents of the current density which vary for different failure modes. The effects of film purity, orientation, grain size, glass overcoat, and solute additions on lifetime are reviewed. Practical guidelines for the design of thin-film interconnections, and for the interpretation of accelerated test data are given.
146 citations