Small-delay defects detection under process variation using Inter-Path Correlation

Abstract

Detection of Small Delay Defects (SDDs) is a major concern in modern circuits using nanometer technologies. They are difficult to test and an important source of test escapes, and even when SDDs do not produce functional failures, they represent a reliability risk. The detection of these defects aggravates in the presence of process variations. In this paper, a methodology to detect SDDs in the presence of process variations using delay correlation information between paths of a circuit is proposed. This methodology exploits the concept that for two highly correlated paths, an important part of the delay variance in one path can be described by the delay variance in the second path. The methodology has been further extended to consider multiple path correlation thus improving the detection of SDDs. This methodology is able to distinguish delay defects from process variations. A metric is also proposed to quantify the SDD screenable variance that represents the percentage of variance where a defect can be detected. A statistical timing analysis framework has been developed and implemented to compute timing information and Inter-Path Correlation (IPC). Spatial and structural correlation, and random dopant fluctuations are considered. Simulation results in 74LS85 and ISCAS85 benchmark circuits evince the feasibility of the proposed methodology.