1997 TMS Annual Meeting: Tuesday Session

EVOLUTION AND ADVANCED CHARACTERIZATION OF THIN FILM MICROSTRUCTURES: Session III: Evolution of Microstructure

Session Chairs: J.E. Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; C.V. Thompson, Dept. of Materials Science and Engineering, M.I.T., Cambridge MA 02139

8:30 am INVITED

GRAIN GROWTH IN POLYCRYSTALLINE THIN FILMS: C.V. Thompson, Dept. of Materials Science and Engineering, M.I.T., Cambridge MA 02139

Polycrystalline thin films are used in a wide variety of applications, especially in electronic and magnetic devices and systems. In these applications, the properties, performance and reliability of polycrystalline films are strongly affected by the average grain size, grain shapes, the way in which grain sizes are distributed and the distribution of grain orientations. These vary with deposition technique and with deposition conditions, and can also be modified through post-deposition processing. The factors which affect the structure and crystallographic texture of polycrystalline films will reviewed and categorized. Approaches for process development for application-specific optimized structures will be outlined.

9:10 am

NEW MICROSTRUCTURAL CHARACTERISTICS OF POLYCRYSTALLINE GOLD THIN FILMS: Alexander H. King, Varun Singh, Department of Materials Science & Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2275

We have made detailed observations of unsupported gold thin films, using transmission electron microscopy. These films embody a strong [111] fiber texture, as found in many FCC metal thin films. Rotations of individual grains about the [111] surface normal are observed and we present a simple model that mimics this behavior, providing a reasonable explanation for it. We will also present an analysis of the triple junctions in the films showing that symmetry is the most significant factor in determining the energy associated with a triple junction. We will show that supposed "U-lines" do not embody the disclinations that are expected on the basis of Bollmann's analysis. Acknowledgment: This work is supported by the National Science Foundation, under grant number DMR-9530314.

9:30 am

MODELING OF GRAIN GROWTH IN THIN FILMS WITH TEXTURE: Harold J. Frost, Johan Grape, Thayer School of Engineering, Dartmouth College, Hanover, NH

We have developed our two-dimensional simulation of grain growth to include several effects which apply for the case of large-grained polycrystalline thin films in which the grains completely traverse the film thickness and the grain boundaries are all nearly perpendicular to the plane of the film. To properly include the effects of texture we must include the following factors which differ among individual grains based on crystallographic orientation: surface energies for the film-substrate and film-covering interface; elastic compliances, and the related strain-energy densities when elastic strains are imposed; yield stresses, which limit the elastic strains and strain-energy densities. In this paper we will expand on previous treatments by explicitly allowing for variations in grain boundary energy and mobility, based on the relative misorientation of neighboring grains. In this case, the grain growth evolution favors pairs of grains separated by low angle (low energy) grain boundaries. Such low energy boundaries generally separate grains of the same texture component. Other effects, such as pinning by surface grooving, pinning by precipitate particles or holes in the film, and solute drag may also be included in the simulations.

9:50 am

POST-PATTERNING MICROSTRUCTURE EVOLUTION OF Al-Cu INTERCONNECT LINES: D. P. Field, TexSEM Laboratories, Inc., 226 W. 2230 N., Provo, UT 84604

Optimization of microstructural features in interconnect lines for integrated circuits is becoming increasingly important for device reliability as the minimum feature size continues to shrink. Recent efforts have clearly demonstrated that not only grain size and precipitate morphologies are affected by the patterning and subsequent anneal, but also the crystallographic texture and grain boundary structure evolve during this process. For narrow lines, the (111) fiber texture sharpens and the near-bamboo grain structure is controlled by interface area minimization and grain boundary energy minimization. The current work describes the competing energetics associated with the process. Experimental results using orientation imaging microscopy as the analysis technique on Al-1% Cu interconnect lines are shown to support the analyses.

10:10 am BREAK

10:30 am INVITED

CRYSTALLOGRAPHIC TEXTURE EVOLUTION DURING FILM FORMATION AND ANNEALING IN SPUTTERED Al ALLOY/Ti AND Al ALLOY/TiN/Ti LAYERS: J.E. Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; P.R. Besser, J. Williams, Advanced Micro Devices, Sunnyvale, CA 94088; D.K. Knorr, Rennselaer Polytechnic Institute, Troy, NY 15128

Ti, TiN and Al alloy thin films comprise the basis for patterned metallization interconnects in advanced integrated circuit devices. Ti in particular has been shown to provide increased reliability of the primary Al conductor against electromigration-induced failures. A proposed mechanism is for this improvement is increased Al (111) film fiber texture due to the presence of the Ti underlayer. A review of extensive Al texture characterization by x-ray diffraction methods will be presented for various Ti, TiN, and Al layering schemes and sputter deposition conditions. Factors such as substrate surface energy, substrate roughness, Al grain growth, and "texture inheritance" between layers will be discussed. Deposition and processing schemes for improved Al (111) texture and improved interconnect reliability will be provided.

11:10 am

THE EFFECT OF MICROSTRUCTURE AND LOCAL MICROSTRUCTURE VARIATIONS ON ELECTROMIGRATION FAILURE DISTRIBUTIONS: Dirk D. Brown, AMD, Sunnyvale, CA 94088; John E., Sanchez, Jr., University of Michigan, Ann Arbor, MI 48109; Matt A. Korhonen, Che-Yu Li, Cornell University, Ithaca, NY 14850

In narrow metal lines used for chip level interconnects, the electromigration reliability is affected by variations in the microstructure. Electromigration failure distributions were obtained experimentally for six different Al-Cu interconnect widths, ranging from 1mm to 8mm. Or each of these line widths, the microstructure was characterized (using TEM) and the initial stress distribution was calculated. This information was used, with a flux divergence model, to simulate the entire failure distribution for each line width. These simulations, when compared to the experimental failure distributions, were used to quantify important material parameters, such as atomic diffusivities and failure criteria. This information, in turn, can be used to accurately extrapolate electromigration data. A detailed failure analysis was carried out on the simulated lines to study the effect of microstructure variations on electromigration failure.

11:30 am

LOCAL GRAIN BOUNDARY STRUCTURE CHARACTERIZATION IN VOIDED COPPER INTERCONNECTS: R.R. Keller, National Institute of Standards and Technology, Materials Reliability Division, 325 Broadway, Boulder, CO 80303; J.A. Nucci, Cornell University, School of Electrical Engineering, Phillips Hall, Ithaca, NY 14853; D.P. Field, TexSEM Laboratories, Inc., 226 West 2230 North #120, Provo, UT 84604

We have characterized grain boundary structures and local textures in oxide passivated copper lines which had undergone thermal stress-induced voiding. Grain boundary misorientations and the crystallographic character of boundary planes were determined for individual grain boundaries using electron backscatter diffraction in the scanning electron microscope as well as focussed ion beam images. We have summarized the data for a number of boundaries immediately adjacent to voids and made direct comparisons to boundaries from regions which remained intact. These data were acquired from the same lines, and so represent measurements from material with identical thermal histories. The results suggest that significant variations in local structure exist in narrow lines, and that those local regions associated with more favorable kinetics are more susceptible to void formation and growth.