A Monte Carlo/FEM investigation on optimal cross-section of high speed ULSI interconnects with respect to RC-delay

Abstract

- Increasingly complex and realistic simulations including 3D visualizations of various physical and chemical phenomena, the modeling of artificial intelligent behavior, real time image processing etc. are only some of the continuously expanding and improving applications of computers. The key to these computational demanding tasks are the rapid advances of ULSI ICs, mainly CPUs and DRAMs. This constant progress of available computational power at a given hardware price is primarily achieved by decreasing minimum feature sizes of ULSI interconnects and devices, currently on the order of 150nm, increased complexity and increased clock frequencies approaching the multi-GHz range. However, the influence of parasitic electromagnetic effects on signal delay and power dissipation is becoming a dominating and limiting factor for further improvements of ULSI ICs. Generally, copper (Cu) or aluminum (Al) interconnects with nearly rectangular or trapezoidal cross sections are used. It is common practice to optimize RC-delay of such interconnect wires by modifying the height/width ratio. However, a further reduction of the achieved typical RC/l2values, practically limited by the present materials being used, would be highly desirable. An extended Monte Carlo search for a potentially optima], arbitrarily shaped, non-rectangular cross section has been performed. A genera] purpose FEM tool (ANSYS-Multiphysics & CAMACO) was employed. It allows the precise determination of capacitances of arbitrarily shaped objects, generated from splines, via the conservation of electrostatic field energy.