Influence of the Seed Layer and Electrolyte on the Epitaxial Electrodeposition of Co(0001) for the Fabrication of Single Crystal Interconnects

Abstract

Co electrodeposition was performed onto single crystal Ru(0001) and polycrystalline Ru films to study the influence of such seed layers on the growth of epitaxial Co(0001). The effect of misfit strain on the electrodeposited Co(0001) films was studied using 60 and 10 nm-thick Ru(0001) seed layers, where the misfit strains of the Co layer on the two Ru(0001) seed layers are 7.9% and 9.6%, respectively. Despite a large misfit strain of 7.9%, the planar growth of Co(0001) was achieved up to a thickness of 42 nm before a transition to island growth was observed. Epitaxial Co films electrodeposited onto 10 nm Ru(0001) showed increased roughness when compared with Co electrodeposited onto the 60 nm seed layer. Co electrodeposition onto polycrystalline Ru resulted in a rough, polycrystalline film with faceted growth. Electrochemical experiments and simulations were used to study the influence of [Co2+] and solution pH on the throughput of the electrodeposition process. By increasing [Co2+] from 1 to 20 mM, the deposition rate of Co(0001) increased from 0.23 nm min−1 to 0.88 nm min−1 at an applied current density of −80 μA cm−2.

Review–On Epitaxial Electrodeposition of Co, Cu, and Ru for Interconnect Applications

“…Co respectively, and it has been assumed that the Ru layer has fully relaxed its misfit strain relative to sapphire following the post-sputter deposition annealing treatment and has adopted its bulk lattice parameters. 7,8,21 In the case of an unrelaxed Ru seed layer, the misfit strain would be 9.6%.…”

“…Additional details of the seed and electrodeposited layer preparation are given in. [7][8][9][10][16][17][18][19][20] Characterization of electrodeposited films.-The films were characterized using X-ray reflectivity (XRR), X-ray diffraction (XRD), scanning electron microscopy (SEM), electron back scatter diffraction (EBSD), scanning/transmission electron microscopy (S/ TEM), selected area electron diffraction (SADP), and energy dispersive X-ray spectroscopy (EDS). Cross-sectional samples for S/TEM were prepared by focused ion beam milling.…”

“…6 Given that electron scattering from grain boundaries is a major contributor to the resistivity rise, this work summarizes recent efforts on room-temperature epitaxial electrodeposition of single crystal and bicrystal films tens of nanometers in thickness, using Co, Cu and Ru as three metals of choice. [7][8][9][10] Epitaxial metals are routinely obtained by vacuum deposition, but require temperatures of several hundred degrees. In contrast, epitaxial electrodeposition of metals can be done at room temperature, but it requires a conductive seed layer.…”

Acceleration Mechanism of Triethanolamine in Electroless Bath for Pure Cobalt Deposition

“…When the line width of copper interconnects is less than 7 nm, the electrical resistivity of copper rapidly rises at the critical dimension of the back-end-of-line (BEOL) due to increasing electron scattering from small copper particles and diffusing surfaces. [1][2][3][4][5][6] Meanwhile, the copper interconnect requires a TaN barrier layer with a thickness of about 2 nm to prevent metal from diffusing into the Si/SiO 2 layer, [7][8][9][10][11][12][13] which also reduces the effective filling volume of the interconnection line and results in an additional increase in interconnection resistance. 14 Metallic cobalt has a shorter electron mean free path (10 nm) than that of copper (39 nm) and its electrical resistivity rises slowly upon the critical dimension of BEOL.…”

“…Therefore, it is highly recommended the use of metallic cobalt as the next-generation interconnect metal to break the bottleneck of the up-coming communication equipment revolution by Intel and Advanced Semiconductor (ASE). 16 Although the cobalt interconnects in integrated circuit (IC) has been fabricated by bottom-up electroplating Co deposition, 17 there are still some challengeable issues such as: (i) the hydrogen evolution occurring during the electroplating process, 4 and (ii) the surface inhomogeneity of the deposited cobalt film. 18 Electroless plating, whose seed layer is not necessary, is an efficient means of filling high-aspect-ratio holes and has become increasingly significant in the industry.…”