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...
We present an in-depth electrical characterization of contact resistance in carbon nanostructure via interconnects. Test structures designed and fabricated for via applications contain vertically aligned arrays of carbon nanofibers (CNFs) grown on a thin titanium film on silicon substrate and embedded in silicon dioxide. Current-voltage measurements are performed on single CNFs using atomic force microscope current-sensing technique. By analyzing the dependence of measured resistance on CNF diameter, we extract the CNF resistivity and the metal-CNF contact resistance.
High-frequency operation with ultrathin, lightweight, and extremely flexible semiconducting electronics is highly desirable for the development of mobile devices, wearable electronic systems, and defense technologies. In this work, the experimental observation of quasi-heterojunction bipolar transistors utilizing a monolayer of the lateral WSe-MoS junctions as the conducting p-n channel is demonstrated. Both lateral n-p-n and p-n-p heterojunction bipolar transistors are fabricated to exhibit the output characteristics and current gain. A maximum common-emitter current gain of around 3 is obtained in our prototype two-dimensional quasi-heterojunction bipolar transistors. Interestingly, we also observe the negative differential resistance in the electrical characteristics. A potential mechanism is that the negative differential resistance is induced by resonant tunneling phenomenon due to the formation of quantum well under applying high bias voltages. Our results open the door to two-dimensional materials for high-frequency, high-speed, high-density, and flexible electronics.
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