As integrated circuits and their components continue to scale downward, the dimensions of metal interconnects and contacts between components are also shrinking. One result is that the resistance in these connectors is increasing. To achieve more compact, faster electronic devices, resistance must be kept to a minimum so that further scaling is feasible.
The slowing effect produced by this higher resistance is often referred to as resistance-capacitance delay (or RC delay) and affects circuits in a variety of ways. Among its undesirable effects, RC delay can degrade the speed at which data are written to and read from DRAM structures via the bitline. In addition, higher resistance leads to higher power consumption, an undesirable side effect for mobile technologies.
The easiest means of lowering line resistance would be to increase the volume of the conducting metal, i.e., make the wires wider and taller. However, wider wires restrict scaling, and taller wires increase capacitance and pose greater etch challenges. Consequently, lowering wire resistance in leading-edge devices focuses on improving the properties of the conducting material, tungsten (W) in case of DRAM bitlines.
The resistance of a conductor is a function of the density of scattering sites encountered by electrons as they move through it. Impurities in the film, grain boundaries, and surface roughness are some of the impediments that slow the electrons down. The Versa XLR2 W PVD chamber reduces interconnect resistance by depositing purer and smoother tungsten film with resistivity 10-15% lower than tungsten deposited using current technology.
The new system achieves this enhanced quality by means of innovations to key hardware components, such as the source magnetron; novel process chemistry; and modulation of plasma characteristics. A scaling enabler, the lower-resistance tungsten produced by the Versa XLR2 W system will extend the use of tungsten as the bitline metal in DRAM technology for 1xnm nodes. The animation below explains how the system’s superior film improves device performance.