NEC touts LSI yield-simulation “breakthrough”

June 15, 2007 – NEC Corp. and NEC Electronics Corp. say they have jointly developed a “breakthrough” yield-evaluation method to enable robust design of low-power, high-performance system LSIs.

The technique uses 3D technology-computer-aided design (TCAD) modeling in the early stages of mass fabrication to evaluate intrinsic fluctuations in device performance, which NEC says is a major obstacle to stable LSI circuit functionality. The new “variation-aware design technology” predicts the random variations within individual devices and the impact of those variations on circuit performance by very large-scale statistical circuit simulation.

Two key advancements with the method include:

– Analysis of performance fluctuations of deeply scaled transistors with accurate 3D atomistic process/device simulation, and precise measurement of the microscopic roughness of the device’s critical geometry. The new computer simulations are capable of calculating 3D positions of every impurity atom in the silicon crystal, and can predict device characteristics for multiple devices as necessary by considering the intrinsic random fluctuations in accordance with specific fabrication processes, NEC explains.

– Converting device characteristic fluctuations into a compact statistical model for very large-scale circuit simulation. This enables efficient statistical circuit simulation for calculating design windows and evaluating areas where productivity can be improved through ease of manufacturing, while maintaining circuit speed and functionality. NEC notes that previously, the mathematical formula for analytical approximation was believed to be incapable of expressing the realistic/practical variations of individual device characteristics, particularly before the stages of establishing new device architecture and mass production capabilities.

NEC and NEC Electronics say they will continue to carry out research in cooperation with Japan’s MIRAI project, to take into consideration the emergence of new variation effects and future mitigation technologies in the future.


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