Monte Carlo Analysis of Propagation Delay Deviation due to Process Induced Line Parasitic Variations in Global VLSI Interconnects

Abstract

Process variation has recently emerged as a major concern in the design of circuits including interconnect in current nanometer regime. Process variation leads to uncertainties of circuit performances such as propagation delay. The performance of VLSI/ULSI chip is becoming less predictable as MOSFET channel dimensions shrinks to nanometer scale. The reduced predictability can be ascribed to poor control of the physical features of devices and interconnects during the manufacturing process. Variations in these quantities maps to variations in the electrical behavior of circuits. The interconnect line resistance and capacitance varies due to changes in interconnect width and thickness, substrate, implant impurity level, and surface charge. This paper provides an analysis of the effect of interconnect parasitic variation on the propagation delay through driverinterconnect-load (DIL) system. The impact of process induced variations on propagation delay of the circuit is discussed for three different fabrication technologies i.e 130nm, 70nm and 45nm. The comparison between three technologies interestingly shows that the effect of line resistive and capacitive parasitics variation on propagation delay has almost uniform trend as feature size shrinks. However, resistive parasitic variation in global interconnects has very nominal effect on the propagation delay as compared to capacitive parasitics. Propagation delay variation is from 0.01% to 0.04% and -4.32% to 18.1% due to resistive and capacitive deviation of -6.1% to 25% respectively.

Monte Carlo analysis of propagation delay due to process induced line parasitic variations in VLSI interconnects

“…Contradictorily, as per the results observed in this work it is observed that although the deviation in delay is more pronounced with increase in line capacitance variation, but these variations have almost same magnitude as the process technology changes from 130nm to 45nm. The delay variations are from -4.32% to 18.1 % due to capacitive deviation of -6.1% to 25% [16]. Now, Table-II shows variation in propagation delay due to deviations in resistance for different fabrication technologies.…”

“…Moreover, these variations are in same magnitude as the process technology changes from 130nm to 45nm. The delay variations were from -0.01% to 0.04 % due to resistive deviation of -6.1% to 25% [16].…”