Screening small-delay defects using inter-path correlation to reduce reliability risk

• Detection of small delay defects under presence of process variations.
• Delays in the slack-time interval and even delays in shorter paths can be detected.
• Inter-Path delay correlation information is used to screen out small delay defects.
• The output signal can be captured at multiple observation intervals.
• Test quality improves leading to higher product reliability.

Subtle defects such as low resistive vias and high resistive shorts cause Small-Delay Defects that are hard to detect even by advanced test methodologies. Detection of these defects aggravates with process variations becoming an important source of test escapes. Furthermore, these defects may degrade with time posing a reliability risk. In this paper, a novel methodology to detect SDDs in the presence of process variations using delay correlation information between logic paths of a circuit is proposed. This methodology exploits the concept that for two correlated paths, a part of the delay variance in one path can be described by the delay variance in other path. Using multiple path prediction allows to further improve the detection of SDDs. A path-based statistical timing analysis framework has been developed and implemented to compute timing information and inter-path correlation. Spatial and structural correlation, and random dopant fluctuations are considered. Simulation results in ISCAS85 benchmark circuits show that the proposed methodology is able to detect SDDs in the slack interval and to distinguish delay defects from process variations. The obtained results give indication of the promising capabilities of the proposed technique to detect “very” small-delay defects. Hence, test quality is improved leading to higher product reliability.