Self-Assembled Nano-Stuffing Structure in CVD and ALD Co(W) Films as a Single-Layered Barrier/Liner for Future Cu-Interconnects

Abstract

Cobalt film with tungsten [Co(W)] has the potential to be an effective single-layered barrier/liner in interconnects, due to its good adhesion with Cu, low resistivity compared with TaN, and comparable barrier properties to TaN. To reduce the resistivity of Co(W), oxygen-free Co(W) was fabricated from oxygen-free precursors, bis(N-tert-butyl-N′-ethylpropionamidinato) cobalt and bis(tert-butylimino)bis(dimethylamino) tungsten, by chemical vapor deposition (CVD) and atomic layer deposition (ALD). Our results showed that W addition improved the barrier properties of both CVD-Co(W) and ALD-Co(W) against Cu diffusion. The diffusion coefficient of Cu in Co(W) was reduced by W addition. The activation energy of Cu in CVD-Co(W) and ALD-Co(W) was 1.5 eV and 1.7–1.8 eV, respectively; whereas that in CVD-Co was 1.0 eV. Improvement in the barrier properties of Co(W) was attributed to the amorphous-like structure created by W. High-resolution transmission electron microscopy and multivariate spectral analysis of the nanoscale properties of Co(W) revealed that the improvement in the barrier properties was due to the self-assembled segregation of W atoms at the grain boundary. The segregated W atoms in both CVD-Co(W) and ALD-Co(W) films may act as a stuffing material. These results suggest Co(W), especially ALD-Co(W), as a promising material for Cu-interconnects in future ultra-large-scale integrated circuits.

Role of W and Mn for reliable 1X nanometer-node ultra-large-scale integration Cu interconnects proved by atom probe tomography

“…14 Mn coexisted with W, suggesting segregation at the grain boundaries of the Co. Figure 3 shows longitudinal elemental profiles within the 1.0-nm-diameter cylindrical bodies in the annealed Cu(Mn)/Co(W) stack (sample (i)-2), corresponding to [I] the middle of the Co grain and [II] the grain boundary of Co. In the center of the Co grain, W mainly segregated at the interface between Cu and Co, which is consistent with the TEM-EDX measurements, i.e., a Co(W) shell encapsulating Co grains, 14 whereas Mn was not detected in this area. Stacking of Cu/ Mn/W/Co was detected at the grain boundaries of Co, indicating that the Mn atoms diffused out completely from the Cu(Mn) layer, and then segregated at the grain boundaries of Co at the Co(W) shell.…”

“…Co(W) can be used to form a combined diffusion barrier and liner, [11][12][13][14] and Co(W) grown by atomic layer deposition (ALD) has been shown to exhibit favorable adhesion strength with Cu compared with Ta, together with a lower resistivity than TaN, and provides comparable diffusion barrier properties to TaN. 11,12,14 These properties have been evaluated numerically in previous studies; the diffusion barrier property has been investigated in Co(W) based on the Cu diffusion coefficient, and the adhesion strength has been investigated by evaluating the wetting angle of Cu grains formed by annealing the Cu film overlying Co(W).…”

“…11,12,14 These properties have been evaluated numerically in previous studies; the diffusion barrier property has been investigated in Co(W) based on the Cu diffusion coefficient, and the adhesion strength has been investigated by evaluating the wetting angle of Cu grains formed by annealing the Cu film overlying Co(W). 15,16 In addition, transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDX) studies have shown that W segregates within the grain boundaries of Co, indicating that W acts to prevent the diffusion of Cu through the grain boundaries of Co, and Co provides good adhesion to Cu.…”

“…15,16 In addition, transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDX) studies have shown that W segregates within the grain boundaries of Co, indicating that W acts to prevent the diffusion of Cu through the grain boundaries of Co, and Co provides good adhesion to Cu. 11,14 Future aggressive scaling will eventually require ultrathin barriers; e.g., the 17-nm node scheduled for fabrication in 2017 requires a 1.5-nm-thick barrier layer, 17 in which the diffusion barrier properties cannot be achieved using current methods, largely due to the existence of pinholes formed within the barrier layer. 18 This represents another challenge for Cu interconnects in order to realize a robust Cu diffusion barrier.…”

“…The W content was optimized based on the results of our previous studies to achieve good adhesion strength with Cu with favorable barrier properties and resistivity. 11,13,14,16 Co[ t Bu-Et-(Et)amd] 2 , bis(tert-butylimido)-bis-(dimethylamino)tungsten(IV) [BTBMW], and NH 3 were used as the Co precursor, W precursor, and reducing agent, respectively, and were selected as a suitable precursor combination to eliminate the incorporation of O impurities into the film. Details of the ALD of Co(W) have been reported previously.…”