Experimental Evaluation of Ternary Systems for VLSI Microelectronics.
Abstract
This work contains both theoretical and experimental results for ternary systems. The theoretical part starts with a compilation of bulk data. Group VIII metals such as Fe, Co, Ni, Pd and Pt form stable ternary phases with other transition metals. This tendency is explained using an empirical approach where parameters affecting phase formation and solubility are electron affinity, atomic radii and valency. Metal -dopant compound formation is also reviewed for Metal-Boron -Si systems. Following the literature review, the validity of other models is discussed. Experimentally, thin film growth of Ti _{rm 4}Ni_4 Si_7, Ti_ {0.75}Co_{0.25} Si_2, TiCoSi, Ti _4Co_4Si_7 and ZrCuSi_2 is observed for the first time. Crystallographic structures and electrical properties of selected compounds are presented. Samples are prepared by Rapid Thermal Processing (RTP) in vacuum. RTP is shown to be also advantageous to form smooth low resistivity silicides such as TiSi_2, CoSi _2 (15-18 muOmega.cm) and ZrSi_2 (34 mu Omega.cm). The ternary phases can be prepared either by reacting bilayers on Si or by processing a metal overlayer on a silicide. For metal bilayers, the sequence of evolution usually starts with the formation of intermetallic compounds. Above 550^circC, Si becomes mobile leading to the growth of ternary phases. The metal in excess with respect to the stoichiometry of the ternary reacts with Si yielding binary silicide which is segregated in a separate layer only if the diffusing metal is involved. The formation of Cu_3Si and its instability in contact with O are analyzed. Decomposition of the silicide is accompanied by room temperature oxidation of Si related to the surface catalytic action of Cu atoms in dissociating O_2 molecules. Small atoms such as Co, Ni and Cu are fast diffusers in silicides, but preliminary results indicate that Cu might be an interesting alternative to Al. For Cu/ZrSi _2 structures, three stages of insertion of Cu atoms into twin habit planes exist. For all the experiments performed, Auger Electron Spectroscopy reflects modifications of the density of states caused by metal d-Si 3p bonding. The global approach combining thin film and bulk samples offers new insights for the future use of multilevel metallizations in submicron VLSI manufacturing processes.
- Publication:
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Ph.D. Thesis
- Pub Date:
- January 1990
- Bibcode:
- 1990PhDT.......204S
- Keywords:
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- Engineering: Materials Science; Engineering: Electronics and Electrical; Physics: Condensed Matter