1997 TMS Annual Meeting: Monday Session

ADVANCES IN ELECTRICALLY CONDUCTIVE MATERIALS: Session II

Session Chairperson: M.E. Fine, Northwestern University, Evanston, IL 60208

2:00 pm INVITED

TRANSITION METAL CARBIDES AND NITRIDES FOR ELECTRONIC DEVICES: Wendell S. Williams, Department of Physics, University of Illinois, Urbana, IL 61801

The need for thermally stable, diffusion-resistant but electronically conducting materials for interconnects in ultra large scale integrated circuits has led to the successful application of transition metal carbides and nitrides, particularly TiN. Another application is the use of superconducting NbN to make Josephson junctions NbN/Si/Nb and Nb/MgO/NbN. And high-temperature resistors with nearly zero temperature coefficients have been made from TaN. This family of materials, sometimes called "metallic ceramics," can be deposited as thin films by several processes, including reactive sputtering, metal-organic chemical vapor deposition and plasma-assisted chemical vapor deposition. An interesting but potentially troublesome characteristic of these NaCl-structured materials is their wide range of deviation from stoichiometry, involving many percent random atomic vacancies, scattering centers for conduction electrons. Hence film preparation requires that the non-metal/metal ratio be close to unity. It is not widely recognized that these defect-ridden crystal structures are non-equilibrium phases: when cooled slowly from high temperatures, some develop ordered phases with lower resistivities.

2:30 pm INVITED

ELECTROMIGRATION IN SUBMICRON Al-0.5% Cu INTERCONNECTS FOR SILICON ULSI: J.A. Prybyla, S.P. Riege, A.W. Hunt, Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974

Systematic studies of the influence of local microstructure on electromigration (EM) dynamics in submicron Al(0.5 wt % Cu) interconnects were performed using in-situ transmission electron microscopy (TEM) techniques. This approach has allowed us to observe in real-time voids forming, growing, migrating, pinning, failing a runner, and healing, all with respect to the detailed local microstructure of the runners. Here we will report and describe how grain boundaries dramatically influence almost all aspects of EM-induced void and failure dynamics in submicron runners. We also find a striking change in EM-mechanism as a function of temperature in the range 200-300°C. Studies as a function of linewidth and passivation state were also performed. Our findings have important implications for both electromigration modeling and conventional reliability testing.

3:00 pm INVITED

DOPANT ACTIVATION OF HEAVILY-DOPED Si BY HIGH CURRENT DENSITY: J.S. Huang K. N. Tu, Department of Materials Science & Engineering, UCLA, Los Angeles, CA 90095-1595

Novel dopant activation in the heavily boron-doped p+-Si was created by applying an electrical current of high current density. The heavily boron-doped p+-Si was obtained by ion implantation and annealed at 900°C for 30 min to achieve a partial boron activation. For additional activation, we gradually applied current until a current density of 2.5X10E7 A/cm2 was reached. The resistance of the p+-Si responded by a gradual increase, then it decreased with a precipitous drop. The resistance was reduced by a factor of 5 to 18. Mechanisms of the novel dopant activation will be proposed. Dopant activation in the heavily arsenic-doped n+-Si will also be discussed.

3:30 pm BREAK

3:50 pm INVITED

DEVELOPMENT OF LOW THERMAL-EXPANSION, HIGH-CONDUCTIVITY ALLOYS BASED ON THE Cu-Fe-Ni TERNARY SYSTEM: R.D. Cottle, R.K. Jain, C.C. Hays, Z. Eliezer, L. Rabenberg, Center for Materials Science and Engineering, The University of Texas at Austin, Austin, TX 78712; M.E. Fine, Northwestern University, Evanston, IL 60208

The FCC phase in Cu-Fe-Ni ternary system contains a miscibility gap within which tie-lines extend from nearly pure Cu toward the Invar composition, Fe - 36% Ni. This suggests that it should be possible to prepare alloys containing isotropic distributions of Invar within high conductivity, Cu-rich, matrices, and that the Invar fraction can be controlled by selecting starting compositions at various points along the tie line. The resulting combinations of low thermal expansion with high electrical and thermal conductivity will be of interest in the electronic circuit packaging industry. Technical difficulties in developing such alloys arise from incomplete solid solubility at high temperatures at the Cu-rich end of the series and from the slow approach to complete chemical phase separation at low temperatures. Quaternary element additions and mechanical deformation processes are being explored as approaches to creating more nearly homogeneous starting alloys. Microstructural developments and electrical and thermal properties will be reported and discussed.

4:20 pm

PROCESS OPTIMIZATION OF HIGH-STRENGTH, HIGH-CONDUCTIVITY Cu-Cr IN-SITU COMPOSITE: H. G. Suzuki, K. Adachi, S. Tsubokawa, T. Takeuchi, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305, Japan

High-strength, high-conductivity Cu-Cr in-situ composites were developed through the optimization of various process variables. Ingots were obtained by vacuum induction melting. Dendritic Cr was in-situ precipitated during solidification. After hot forging and solution treatment at 1000C, repeated cold working was performed to get fine lamellar spacing of single crystalline Cr second phase. The analysis of microstructure by TEM showed dynamic recrystallization of Cu matrix and fine distribution of Cr precipitates. These structures give the strength level of 900 MPa and relative conductivity, IACS, of 78%. The mechanism of high strength and high conductivity will be discussed.

4:40 pm

THE CHARACTERISTICS OF ELECTRICAL CONDUCTIVITY AND PRECIPITATION OF Cr BY AGING IN Cu-Cr IN-SITU COMPOSITE: J. Yan, H.G. Suzuki, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305, Japan

Aging treatment is one of the most important materials processing techniques for obtaining high electrical conductivity in Cu in-situ composite. In this work, we systematically investigated the effect of Cr precipitation on electrical conductivity of a Cu-15 wt % Cr in-situ composite, by means of aging treatment, electrical conductivity measurement, scanning electron microscopy, analytical electron microscopy, high resolution electron microscopy and X-ray lattice parameter measurement. The optimum aging condition for obtaining peak electrical conductivity has been determined. In addition, it is found that an appropriate amount of cold working can further enhance the electrical conductivity of the composite. The related mechanism has also been studied.