Interdiffusion within model TiN/Cu and TiTaN/Cu systems synthesized by combinatorial thin film deposition

Marlene Mühlbacher

Research output: ThesisDoctoral Thesis

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Abstract

Continued device miniaturization in microelectronics calls for a fundamental understanding of diffusion processes and damage mechanisms in the Cu metallization/TiN barrier layer system. Thus, the starting point of the present study is a combined experimental and theoretical examination of lattice diffusion in ideal single-crystal TiN/Cu stacks grown on MgO(001) by unbalanced DC magnetron sputter deposition. After a 12 h annealing treatment at 1000 °C, a uniform Cu diffusion layer of 7-12 nm is observed by scanning transmission electron microscopy and atom probe tomography (APT). Density-functional theory calculations predict a stoichiometry-dependent atomic diffusion mechanism of Cu in bulk TiN, with Cu diffusing on the N sublattice for the experimental N/Ti ratio of 0.92. These findings are extended to a comparison of grain boundary diffusion of Cu in dense polycrystalline TiN sputter-deposited on Si at 700 °C and underdense polycrystalline TiN grown on Si without external substrate heating. While the Cu diffusion path along dense TiN grain boundaries can be restricted to approximately 30 nm after a 1 h annealing treatment at 900 °C as visualized by 3D APT reconstructions, it already exceeds 500 nm after annealing at 700 °C in the underdense low-temperature TiN barrier. In this case, the formation of the Cu3Si phase, which characteristically grows along the close-packed directions in Si, is identified as the main damage mechanism leading to complete barrier failure. To meet the low-temperature processing needs of semiconductor industry and at the same time exploit the improved performance of dense polycrystalline barrier layers, deposition of TiTaN barriers on Si is demonstrated by a reactive hybrid high-power impulse/DC magnetron sputtering process, where barrier densification is achieved by pulsed irradiation of the growth surface with only a few at.% of energetic Ta ions without external substrate heating. These barrier layers delay the onset of Cu grain boundary diffusion to temperatures above 800 °C (1 h annealing time) and are therefore capable of competing with TiN barriers deposited at 700 °C.
Translated title of the contributionInterdiffusion in mit kombinatorischen Beschichtungsprozessen hergestellten TiN/Cu und TiTaN/Cu-Schichtsystemen
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Schalk, Nina, Co-Supervisor (internal)
  • Mitterer, Christian, Assessor A (internal)
  • Hultman, Lars, Assessor B (external), External person
Publication statusPublished - 2015

Bibliographical note

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Keywords

  • Diffusion
  • Cu
  • TiN
  • Sputter Deposition
  • Thin Film Deposition
  • Transmission Electron Microscopy
  • TEM
  • Atom Probe Tomography
  • APT

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