Real-time spectroscopic ellipsometry study of ultrathin diffusion barriers for integrated circuits

Abstract

The objective of this work is to monitor the growth process and the thermal stability of ultrathin tantalum nitride barrier nanostructures against copper diffusion in integrated circuits using real-time spectroscopic ellipsometry (RTSE). Single layers of copper and bilayer films of copper and tantalum nitride were produced on Si͑111͒ substrates using unbalanced magnetron sputtering. The RTSE data was simulated using the Bruggeman effective medium approximation and a combined Drude-Lorentz model to obtain information about the growth process, film architecture, interface quality, and the conduction electron transport properties for these structures. The results deduced from the RTSE were verified by characterizing the structural and the chemical properties of the fabricated films using x-ray diffraction, Auger electron spectroscopy, and Rutherford backscattering. The effectiveness of the tantalum nitride barrier to stop the diffusion of copper into silicon was evaluated, monitoring their optical properties when annealed at 720°C. The dielectric function of the films changed from a metallic to an insulating character when the diffusion proceeded. Also, the RTSE provided valuable information about the microstructure and the kinetics of the phase transformations that occur during heat treatment.

Optical Properties and Plasmonic Performance of Titanium Nitride

“…It has been considered since the early 1970s as a superhard material for protective coatings [ 1 , 2 , 3 , 4 ] and, as such, has been industrially implemented. Its electronic properties were also extensively studied, as they are critical for alternative applications such as diffusion barriers in microelectronic devices [ 5 , 6 , 7 , 8 , 9 ], decorative coatings with bright golden color [ 10 , 11 , 12 , 13 ], ohmic contacts on III-nitride semiconductors [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ] and Schottky contacts on Si [ 22 , 23 ]. Great emphasis has been given to the control of the microstructure of TiN films [ 24 , 25 , 26 , 27 , 28 , 29 ], which are critical for its mechanical and electronic performance.…”

Resistivity of thin Cu films coated with Ta, Ti, Ru, Al, and Pd barrier layers from first principles

“…[2][3][4] This size effect represents a great challenge for the continued down scaling of electronic devices because increased resistivity dramatically enhances heat dissipation and interconnect delay in the integrated circuits. Experimentally, among the several electronscattering mechanisms that contribute to resistivity of Cu interconnects, 1-3,5-7 surface roughness scattering has been identified as a major source to the size effect.…”

Resistivity of thin Cu films with surface roughness

“…The size effect becomes severe below 50 nm, giving rise to ϳ100% increase in the resistivity. [3][4][5] Several scattering mechanisms contribute to the resistivity of Cu interconnect, and the problem of size effect is usually addressed by decomposing the total resistivity into several contributions using the Matthiessen's rule, 6 = b + im + s + g , ͑1͒…”