Thermal stability of Ti/Mo and Ti/MoN nanostructures for barrier applications in Cu interconnects

Abstract

This work focuses on the barrier capabilities of sputter deposited Ti/Mo and Ti/MoN nanofilms against diffusion of Cu into Si substrates. The thermal stability of the corresponding bi-layer barrier structures is investigated after annealing Cu/barrier layer/Si samples at different temperatures in N(2) for 5 min. The drastic increase in sheet resistance of Cu and the probing of Cu(3)Si with x-ray diffraction after high temperature annealing indicate the failure of these barrier structures. The formation of Cu(3)Si at the barrier breakdown temperature is also confirmed by scanning electron microscopy and energy dispersive x-ray spectroscopy. Cu diffusion barrier performance analyses show that a Ti(5 nm)/MoN(5 nm) bi-layer nanostructure fails only after annealing at 800 °C; on the other hand, a Ti(5 nm)/Mo(5 nm) barrier stack is found to break down at 700 °C.

Robust ultra-thin RuMo alloy film as a seedless Cu diffusion barrier

“…2a) and acutely ascendant sheet resistance (Fig. 1), this triangular film could be considered as part of the formation of Cu 3 Si [29,30]. The forming Cu 3 Si in the Cu/Ru/Si stacked films implies that Cu atoms already penetrated through the Ru barrier and reacted with Si.…”

4-nm thick multilayer structure of multi-component (AlCrRuTaTiZr)N as robust diffusion barrier for Cu interconnects

“…However in the 32 or 22 nm generation of semiconductor manufacturing, a more suitable barrier layer is highly demanded because of the microstructure defects of the conventional barrier materials such as columnar boundaries. Therefore, in recent years, diffusion barriers that comprise ternary elements or layered structures have been extensively studied [6][7][8][9][10][11][12][13][14]. Barrier systems with ternary or more components, such as Ta-W-N (50 nm thick) [6], Ru-Ti-N (10 nm) [7], Ta-Ge-(O)N (50 nm) [8], and Ru-Ta-N (15 nm) [9], usually have large lattice distortions and an amorphous structure that reduces the number of viable diffusion paths and effectively increases diffusion resistance.…”

“…Barrier systems with ternary or more components, such as Ta-W-N (50 nm thick) [6], Ru-Ti-N (10 nm) [7], Ta-Ge-(O)N (50 nm) [8], and Ru-Ta-N (15 nm) [9], usually have large lattice distortions and an amorphous structure that reduces the number of viable diffusion paths and effectively increases diffusion resistance. Layered (mostly bilayered) structures, including Ti/MoN (5/5 nm) [10], Ir/TaN (5/5 nm) [11], Ru/TaN (5/5 nm; 3/5 nm) [12,13], and atomic-layer deposited Ru/TaCN (12/2 nm) [14], increase diffusion distance by a layer-interface lattice mismatch, enhance diffusion resistance, and strengthen Cu adhesion. Additionally, segregation-induced self-forming barriers (such as Mn [15]) and organic self-assembled monolayers (of NH 2 SAM, for example, [16]) have also attracted much interest.…”

“…Multi-component-induced lattice distortions and layeredstructure-increased diffusion distances effectively improve the resistance of barrier layers to Cu diffusion [6][7][8][9][10][11][12][13][14]. Therefore, owing to the thermodynamically stable solid-solution structures and severe lattice distortions of multiprincipal-element alloys (called high entropy alloys, HEAs) [17][18][19], individual films and bilayered structures of HEAs and HEA nitrides (denoted as HEANs) with a nanocomposite or amorphous structure and a thickness from 70 to as low as 10 nm have been developed as diffusion barriers [20][21][22].…”

Ru incorporation on marked enhancement of diffusion resistance of multi-component alloy barrier layers

“…However, microstructure defects, such as grain and column boundaries, formed in these conventional barrier layers provide some paths for rapid Cu diffusion and consequently lower the diffusion resistance of the barrier layers. To fulfill the strict demands for Cu interconnects in the manufacturing generations below 65 nm, other barrier systems with ternary components or composition modifications [6][7][8][9][10][11], e.g., Ru-Ti-N and Ru-Ta-N [10,11], and/or of layered structures [12][13][14][15][16][17][18], including Ta/TaN and Ru/TaN [16][17][18], to elongate diffusion distances have received considerable interest and are continually developed. However, proper barrier layers for 32 or 22 nm generation with a low electrical resistivity, an ultra-small thickness around 5 nm, and still a high diffusion resistance have seldom been reported.…”