TaC as a diffusion barrier between Si and Cu

Abstract

The reaction mechanisms and related microstructures in the Si/TaC/Cu metallization system have been studied experimentally and theoretically by utilizing ternary Si-Ta-C and Ta-C-Cu phase diagrams as well as activity diagrams calculated at 800°C. With the help of sheet resistance measurements, Rutherford backscattering spectrometry, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the metallization structure with the 70 nm thick TaC barrier layer was observed to fail completely at temperatures above 725°C because of the formation of large Cu 3 Si protrusions. However, the formation of amorphous Ta layer containing significant amounts of carbon and oxygen was already observed at the TaC/Cu interface at 600°C. This layer also constituted an additional barrier layer for Cu diffusion, which occurred only after the crystallization of the amorphous layer. The formation of Ta 2 O 5 was observed at 725°C with x-ray diffraction, indicating that the oxygen rich amorphous layer had started to crystallize. The formation of SiC and TaSi 2 occurred almost simultaneously at 800°C. The observed reaction structure was consistent with the thermodynamics of the ternary system. The metallization structures with 7 nm and 35 nm TaC barrier layers failed above 550°C and 650°C, respectively, similarly because of the formation of Cu 3 Si. The high formation temperature of TaSi 2 and SiC implies high stability of Si/TaC interface, thus making TaC layer a potential candidate to be used as a diffusion barrier for Cu metallization.

Diffusion barrier properties of AlMoNbSiTaTiVZr high-entropy alloy layer between copper and silicon

“…The sluggish diffusion is also far more pronounced with such a high number of elements, especially at a low deposition temperature, due to the confusion principle [22] and the increased packing density [23]. Finally, the large atomic size differences among the constituent elements will be expected to favor an amorphous structure in preference [20] to a crystalline structure, due to the ability of the former structure to release the total strain energy, although some bonding energy is sacrificed as a result of its reduced coordination number. These factors have led to the formation of nanoscale or amorphous structures in a number of HEA systems that have been produced either by bulk casting or by deposition techniques [8,10].…”

“…Comparison of the maximum working temperature between the present work and other barrier research published recently[16][17][18][19][20] …”

Surface nano-structured silicon carbide thin film produced using hot filament decomposition of ethylene at low temperature on silicon wafer

“…At annealing temperatures above 700°C the TaC becomes predominant (Fig. 4) and, probably, some additional stable Ta-C and may be Ta-O compounds can form [37]. Ferro had discussed the interaction between hot filament and deposited gas [38].…”

Low-Resistivity Ru-Ta-C Barriers for Cu Interconnects

“…12 However, the resistivity of as-deposited Ru 77 Ta 15 C 7 in this study is 143 lX cm, while that of 900°C-annealed film is as low as 20 lX cm. Laurila et al 13 showed that the resistivity of Ta 53 C 47 is 210 lX cm, and 7-nm-thick TaC fails at 550°C for 30 min. For the ternary ruthenium nitride, the 15-nm-thick Ru-Ta-N on SiO 2 /Si substrate fails at 900°C for 30 min; however, no related resistivity result has been shown.…”