Effects of Nitrogen Plasma Treatment on Tantalum Diffusion Barriers in Copper Metallization

Abstract

In this study, the barrier properties of ultrathin Ta, TaN, and nitrogen plasma-treated Ta films were investigated by Cu/Ta͑N͒/Si structure. The barrier properties were evaluated by sheet resistance, film stress, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Nitrogen plasma-treated Ta films possess better barrier performance than sputtered Ta and TaN films. The sheet resistance of Cu/Ta/Si and Cu/TaN/Si increases, apparently, after annealing at 600 and 625°C, respectively. The Cu/30 min plasma-treated Ta/Si is fairly stable up to annealing at 700°C for 1 h. Diffusion resistance of the plasma-treated Ta barrier is more effective. It is believed that a new amorphous layer forms on the surface of Ta film after plasma treatment. The new amorphous layer possesses some nanocrystalline Ta 2 N phases with lattice constant 0.305 nm. It is believed that the amorphous layer containing some nanocrystals can alleviate Cu diffusion into the Si substrate and, hence, improve barrier performance.Copper is an attractive material for interconnection due to its lower electrical resistivity and better electromigration resistance compared to Al-based alloys. Copper is better considered for application in integrated circuits. However, it is well known that copper diffuses quickly in Si substrates and SiO 2 films, which causes degradation of transistor reliability by forming particular impurity levels in the silicon. 1 Because of its ability to rapidly diffuse in silicon and degrade reliability, the development of effective diffusion barrier materials is the most important issue for the realization of Cu interconnection in Si-based integrated circuits. Many materials are used as diffusion barriers in copper metallization system. Refractory metals and their nitrides have been investigated for such applications. Among them, tantalum and tantalum nitride have received the most attention owing to their high thermal stability and resistance to form compounds with copper. Previous studies have shown that tantalum nitride is more desirable than tantalum in terms of barrier effectiveness. However, resistivity of tantalum nitride film is higher than that of tantalum film. 2-4 As the technology moves to 180 nm node and below, a thin barrier layer is necessary to lower the resistance of the total line interconnect and/or via. It becomes inappropriate to use a barrier layer thicker than 30 nm, and hence investigations of the thermal stability and barrier properties of ultrathin barrier layers in the Cu metallization system are important.In this article, we studied the barrier properties and thermal stability of ultrathin Ta-based barrier layers ͑10 nm͒ in the Cu metallization system. Furthermore, a new method to form nitrogen incorporated Ta film with low resistivity and high thermal stability was proposed and investigated. Nitrogen plasma was used to post-treat the Ta diffusion barrier. Properties of barrier layers were evaluated by electrical measu...

First-principles simulations of copper diffusion in tantalum and tantalum nitride

“…The Cu/ fcc-TaN interface structures remain unclear experimentally except that Cu ͑111͒ has been reported as preferred orientation on fcc-TaN substrate. [8][9][10][11][12][13][14]27,28 Therefore, we will study Cu ͑111͒/fcc-TaN ͑111͒ interfaces by including three Cu ͑111͒ layers on top of TaN ͑111͒ substrate in the firstprinciples calculations. [29][30][31][32] All calculations in this paper are carried out based on first-principles density-functional theory ͑DFT͒ with planewave basis and the projector augmented-wave method as implemented in the Vienna Ab initio Simulation Package.…”

“…In this work, we take the experimentally observed orientations of Cu/barrier interface: Cu ͑111͒ layers on top of ͑111͒ surface of fcc TaN, [8][9][10][11][12][13][14] ͑110͒ surface of bcc Ta, 9,10,14 ͑001͒ surface of hexagonal Ta 2 N, 5 and ͑001͒ surface of hexagonal TaN. The interfacial cohesive energy is calculated as a function of terminating surface and in-plane arrangement for each of the substrates.…”

“…On the experimental side, research is mostly concentrated on the growth of TaN thin films, the characterization of fabricated structures, and the annealing test of barrier effectiveness. [5][6][7][8][9][10][11][12][13][14] It has been shown that the presence of N in TaN compounds enhances the resistivity to diffusions 6,7 and the stacking of TaN compounds on Ta layers 11 improves the performance of the barrier materials. However the relationship between the barrier efficiency and material structure has not been established.…”

“…III. The bulk properties of Ta and TaN compounds [5][6][7][10][11][12][13][14] are presented in Sec. III A while the interfacial properties of Cu/TaN system are included in Sec.…”

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

“…[3][4][5] For instance, tantalum and tantalum nitride have been studied the most owing to their immiscibility with Cu and their superior thermal stability. 6 A new challenge facing the semiconductor industry is that the dimensions of Cu interconnected structures continue to shrink, forcing the dimensions of barrier layers to scale down. Consequently, investigating the reliability of ultrathin structures becomes more and more important for the product reliability.…”