1997 TMS Annual Meeting: Tuesday Session

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

Session Chairs: J.P. Sullivan, J.A. Floro, Sandia National Labs, Albuquerque, NM 87185

2:00 pm INVITED

EVOLUTION OF GRAIN STRUCTURE IN THIN FILM REACTIONS: K. Barmak, Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015

The granular nature of polycrystalline thin films is playing an increasingly important role in their performance as the dimensions of the grains and those structures in which the thin films are used become comparable. Consequently, greater attention is being paid to the factors that affect the grain structure of thin films and its evolution. This paper will address the evolution of grain structure during the reaction of polycrystalline thin films. Experimental evidence from calorimetry, x-ray diffraction and transmission electron microscopy studies of a number of thin film systems will be reviewed and the role of reactant phase microstructure in these reactions will be highlighted. Theoretical models that combine nucleation and growth processes in the formation of the product phase will be presented and the impact of heterogeneous boundary nucleation on the evolution of grain structure in thin film reactions will be discussed.

2:40 pm

THE MICROSTRUCTURAL DEVELOPMENT OF THIN FILM COPPER GOLD ORDERED INTERMETALLIC COMPOUNDS: Jonathan Gorrell, Paul Holloway, Dept. of Material Science and Engineering, University of Florida, Gainesville, FL 32611-6400; Hal Jerman, EG&G IC Sensors, 1701 McCarthy Blvd., Milpitas, CA 95035

Recent developments in microelectromechanical systems (MEMS) have created a need for stronger metal thin films that are resistant to stress relaxation. Intermetallic compounds are noted for their strength and resistant to creep, but these properties have rarely been studied in thin films of intermetallics. We have sputter deposited layered structures of copper and gold so that the intermetallic compounds Cu3Au, CuAu and CuAu3 would form. The samples were initial heated to 475°C to allow intermixing of the copper and gold layers and the evolution of the intrinsic and extrinsic stresses were characterized during the process. The samples were then annealed at temperatures where the intermetallic phases would form. The intermetallic phases were tested for strength and stress relaxation using a Tencor Flexus 2320. The microstructure and composition were examined with TEM, EDX, Electron Microprobe, and X-Ray diffraction. This data allows us to relate strength and resistance to stress relaxation to microstructure and the heat of formation of the various copper gold intermetallic compounds.

3:00 pm

CHARACTERIZATION OF GRAIN BOUNDARIES IN Al INTERCONNECTS BY ORIENTATION IMAGING MICROSCOPY: C. Wu, C.L. Bauer, B.L. Adams, W.W. Mullins, Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA

Characterization of microstructure (grain orientation, grain-boundary inclination, microtexture, etc.) in thin-film interconnects is especially important because grain size usually approximates film thickness, thereby enhancing short-circuit diffusion induced by electric fields (electromigration), mechanical stress (stress voiding), temperature gradients (thermomigration), and capillarity (grain-boundary grooving). In this research, grain boundaries in polycrystalline Al interconnects have been characterized by orientation imaging microscopy and analyzed in terms of the interconnectivity of triple junctions. In general, results indicate that a variety of thermodynamic and kinetic properties can be extracted by rapid acquisition and processing of large data sets and correlated with the (five) degrees of crystallographic freedom of individual grain boundaries. Research supported, in part, by the National Science Foundation under Grant DMR-9319896.

3:20 pm

REAL-TIME MEASUREMENTS OF MICROSTRUCTURAL EVOLUTION IN Ag THIN FILMS ON SiO2: Eric Chason, Jerry Floro, Sandia National Laboratories, Albuquerque, NM 87185-1415; Steven C. Seel, Carl Thompson, Massachusetts Institute of Technology, Cambridge, MA

Understanding and controlling the microstructure in thin metal films used for IC interconnects is essential for maintaining high reliability. Although the microstructure of Al films has been heavily studied, the switch to Cu for interconnects in the future will lead to different microstructural evolution than in current technology. In order to study the kinetics of grain growth and texture evolution, we have developed an in situ X-ray system that can measure the concurrent evolution of (111) and (100) textured crystallites during annealing. We present results from the annealing of Ag films, which have similar elastic properties to Cu. This work was supported by the U.S. Department of Energy under contract DE-AC04.

3:40 pm BREAK

4:00 pm INVITED

STRESS RELAXATION AND THERMAL EVOLUTION OF FILM PROPERTIES IN AMORPHOUS CARBON: J.P. Sullivan, Sandia National Labs, Albuquerque, NM 87185

Large stress relaxation is observed in amorphous carbon films deposited by pulsed-laser deposition which are subsequently thermally annealed. In the as-deposited state, the films exhibit very high compressive stress, > 6 GPa, which has been thought to be either necessary or unavoidable in order to form a high percentage of 4-fold coordinated (diamond-like) carbon bonds and which can also hamper important electronic applications of these films. Stress measurements performed in situ and ex situ following thermal annealing up to 600°C indicate the stress may be reduced nearly two orders of magnitude. The stress relaxation is not dominated by interfacial relaxation nor is it accompanied by large scale changes within the film (e.g. graphitization) as indicated by in situ and ex situ electrical measurements, ex situ X-ray reflectivity, Raman spectroscopy, and experiments using different substrates. The bonding structure and mechanisms of thin film evolution in these unique amorphous films will be discussed. Work at Sandia was supported by an LDRD through the U.S. DOEunder contract no. DE-AC04-94AL85000 and by a CRADA.

4:40 pm

MICROSTRUCTURE AND TEXTURE DEVELOPMENT IN CUBIC BORON NITRIDE THIN FILMS: D.L. Medlin, P.B. Mirkarimi, G.F. Cardinale, K.F. McCarty, Sandia National Laboratories, Livermore CA 94551

Cubic boron nitride (cBN) is an sp3-bonded material with many properties and applications that are similar to diamond. Although cBN can be synthesized in bulk form at high temperature and pressure, synthesis in thin film form requires the simultaneous bombardment of the growing film with a high flux of energetic ions. cBN films grow with a unique, layered microstructure in which sp2-bonded graphitic boron nitride initially forms near the substrate interface, and nucleation and growth of the sp3-bonded cubic phase occurs further up in the film. Both the graphitic and cubic layers exhibit strong preferential crystallographic orientations: the graphitic layer possesses a strong in-plane [0002] orientation, whereas the cBN possesses an in-plane [111] orientation. This preferential orientation is consistent with an alignment between the cBN {111} planes and the basal planes of the layer of highly oriented graphitic boron nitride that forms in the initial stages of film growth. This relationship provides insight into the mechanisms controlling the initial nucleation of cBN and subsequent microstructural evolution of the films. This work is supported by the U. S. Department of Energy under contract DE-AC04-94AL85000 and in part by OBES-DMS.

THE FOLLOWING PRESENTATION IS WITHDRAWN
5:00 pm

CHARACTERIZATION OF SrRuO3 THIN FILMS: MICROSTRUCTURE/PROPERTY RELATIONSHIP: F. Chu, Q.X. Jia, C. Adams, T.E. Mitchell, Materials Science and Technology Division, Mail Stop K 765, Los Alamos National Laboratory, Los Alamos, NM 87545; Q. Zhu, Physics Department, Brookhaven National Laboratory, Upton, NY 11973

Metallic oxide SrRuO3 thin films have been grown using pulsed laser deposition on LaAlO3 substrates at different substrate temperatures. The surface morphology and microstructural properties of the SrRuO3/LaAlO3 system have been studied using high resolution synchrotron x-ray diffraction, conventional x-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Electrical properties of SrRuO3 thin films with different microstructures have been measured. It is found that films deposited at 250°C are amorphous, and show semiconductor-like temperature dependence of electrical conductivity. Films deposited at 425°C are crystalline with very fine grain size (100~200Å), and show both metallic and semiconductor-like temperature dependence of the electrical conductivity in different temperature regions. Synchrotron x-ray diffraction and transmission electron microscopy unambiguously indicate that epitaxial [001] and [110] growth of the orthorhombic films takes place for deposition temperature above 650°C, where the [001] texture is dominant. Films deposited at 775°C show a resistivity of 280 mW-cm at room temperature. Microstructures of epitaxially grown films and possibilities for improving the thin film growth are discussed, based on geometric considerations for both film and substrate. The optimized deposition conditions to grow SrRuO3 thin films on LaAlO3 substrates have been found. Possible engineering applications of SrRuO3 thin films with different microstructures are discussed.