Papers

ICMCTF1998 Session H5: Silicon Contact Tehnology

Tuesday, April 28, 1998 1:30 PM in Sunrise Room

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		H5-1 Advanced Contact Metallization for Logic and Memory Applications G. Dixit (Texas Instruments)
2:10 PM		H5-3 Synchrotron X-ray Diffraction Studies of Interfacial Reaction Paths and Kinetics in Al/TiN Bilayer Structures J.-S. Chun, J.R.A. Carlsson, D.B. Bergstrom, I. Petrov, J.E. Greene (University of Illinois); C. Lavoie, C. Cabral, Jr. (IBM-T.J. Watson Research Center) Highly-textured polycrystalline TiN(002) layers, 110 nm thick, were grown on SiO₂ by ultra high vacuum (UHV) magnetron sputter deposition in pure N₂ at T_s = 450 °C. 160-nm-thick Al overlayers with strong inherited (002) texture were then deposited at T_s = 100 °C without breaking vacuum. Synchrotron x-ray diffraction (XRD) was used continuously to follow interfacial reaction paths in-situ as a function of annealing time, t_a (120-1200 sec) and temperature, T_a (500-580 °C). The annealings were carried out in a chamber evacuated to 10^-7 Torr and backfilled with 1 atm He. Local changes in bilayer microstructure and microchemistry were investigated ex-situ using plan-view and cross-sectional transmission electron microscopy (TEM), and scanning TEM, in which cross-sectional and plan-view specimens were analyzed by energy dispersive x-ray (EDX) analysis with 1 nm resolution. The first phase to form during annealing is a continuous 30 nm thick hexagonal AlN with an initial 3-5 nm-thick underlayer of cubic (metastable zinc-blende) structure. This mixed phase AlN layer inhibits further interaction between Al and TiN. With further annealing, Ti, the primary diffusing species, selectively diffuse to the certain Al grains through local weak points in AlN layer, leading to the nucleation of tetragonal Al₃Ti. Dispersed Al₃Ti with a 002 preferred orientation rapidly consume entire Al grains with their growth limited by the original Al column boundaries. Change of integrated XRD peak of Al₃Ti shows nucleation limited Al₃Ti growth with an activation energy E_a of 1.78 eV.
2:30 PM		H5-4 Contact resistance in Copper Metallization T. Nguyen, M. Kobayashi, Y. Ono, L. Charneski, S.T. Hsu (Sharp Microelectronics Technology) Contact resistance of copper with copper, doped poly and Ti silicide underlayers is evaluated. Low contact resistance (0.05 Ohm per 0.7um contact) and good yield are observed for copper to copper contact without barrier material. With barrier material, the resistance increases somewhat, depending on the material and thickness of the barrier. However, yield is much poorer if the barrier material is exposed to air before copper deposition. Via contact resistance of copper with doped poly is higher than with Ti silicide (20 Ohm vs. 1 Ohm for 0.7um contact). Similar to copper/barrier/copper contact, yield is significantly poorer when the barrier is exposed to air before copper deposition. In-situ deposition of barrier and copper deposition seems to be needed for improving contact resistance yield. Contact resistance also increases significantly with high temperature annealing (300-400C), probably due to the degradation of the copper/barrier interface, and not due to copper diffusing through the barrier because the device performance is not effected.
3:10 PM		H5-6 Characterization of Multilayered Ti/TiN Films Grown by Chemical Vapor Deposition J.C. Hu (National Tsing Hua University, Taiwan, ROC); T.C. Chang (National Nano Device Laboratory, Taiwan, ROC); L.J. Chen (National Tsing Hua University, Taiwan, ROC); Y.J. Mei (National Chiao Tung University, Taiwan, ROC); Y.L. Yang (National Nano Device Laboratory, Taiwan, ROC); C.Y. Chang (National Chiao Tung University, Taiwan, ROC) The microelectronics industry had shown an increasing interest in TiN because of its high thermal stability, low electrical resistivity, and good diffusion barrier characteristics. As the device dimensions scale down to deep submicron level, chemical vapor deposition (CVD) for TiN films provided excellent step coverage and uniformity. The improved feature was attributed to favorable surface controlled reactions. However, since the TiN films still have columnar structure by CVD method, Al and Si atoms can diffuse through the fast pathway along TiN grain boundaries. In this work, in order to prevent Al and Si atoms interdiffusion along TiN grain boundaries, the novel multilayered Ti/TiN structure is firstly proposed by chemical vapor deposition. The Ti and TiN films were deposited by plasma enhanced chemical vapor deposition (PECVD) and low pressure chemical vapor deposition (LPCVD), respectively. All the films were deposited by CVD processed in a MRC multichamber cluster tool, using TiCl₄, NH₃ and H₂ as reaction gases. The enhanced multilayered Ti/TiN stack formed a robust barrier against Al/Si interdiffusion and it had some effect on the electrical property of the films. In addition, in order to reduce chlorine content of the films, in-situ NH₃ post annealing and plasma treatment were applied to as-deposited multilayered Ti/TiN films, respectively. The resistivity of the film was found to rapidly reduce by multilayered Ti/TiN structure with in-situ NH₃ plasma post-treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were utilized to investigate the microstructure and crystal orientation. Auger electron spectrocope (AES) was applied to determine the stoichiometry and uniformity along the depth direction. The morphology was studied by a field emission scanning electron microscope (FESEM).
3:30 PM		H5-7 Low Parasitic Resistance Contacts for Scaled ULSI Devices C.M. Osburn, K.R. Bellur (NC State University) Interfacial contact resistivities less than 10^-7 Ohm-cm² will be required for sub 100 nm ULSI devices in order to stay on the historical performance trend. With dimensional scaling, the series resistance per unit width decreases in the device channel region because channel lengths are scaled, while it increases in contacts because the contact length is decreased; for 50 nm devices using conventional contacting technology, the contact resistance is projected to be higher than the channel resistance, and no performance advantage will be obtained by making the device smaller. The challenge in meeting the contacting requirements implicit in the 1997 National Technology Roadmap for Semiconductors is especially difficult in light of the desire to simultaneously contact both n+ and p+ junctions with a single material and given the trend towards lower processing temperatures, in which the equilibrium dopant electrical activity is lower. This talk will describe recent work focused on reducing contact resistivity by maximizing interfacial dopant concentrations and minimizing contact barrier heights. Higher saturated drive currents, due to lowered parasitic series resistance, are observed in deep submicron devices made using silicides as diffusion sources (SADS); this technique eliminates the interfacial dopant segregation that is associated with conventional silicidation. The recrystallization of amorphous layers has been observed to result in non-equilibrium dopant activation which can be as much as ten times the equilibrium value. Finally, the use of heterojunction contacts using Si-Ge in the context of elevated source/drain devices presents another way to achieve lower contact resistance.
4:30 PM		H5-10 Materials Science Issues of Ultra-Shallow Junction Y. Erokhin (Eaton Corporation)