Cell-Internal Defect Detection via Waveform Discrepancy Analysis
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Solution Overview
Problem
Conventional fault detection techniques in integrated circuits are inadequate for modeling real layout-based defects within library cells, as they primarily focus on faults between cell instances and not inside cells, leading to unsatisfactory detection of cell-internal defects.
Innovation Solution
A defect detection system that compares waveforms of faulty and fault-free cells over a time-domain range to identify discrepancies, categorizing defects and improving deterministic detection of cell-internal defects by analyzing voltage and current waveforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fault models are used that assume faults only occur between library cell instances, then the fault detection process is simple and follows standard ATPG procedures, but cell-internal defects within library cells cannot be detected
Solution Approach 1:
The patent segments the fault detection process into two distinct parts: (1) standard ATPG for inter-cell faults using conventional fault models, and (2) a specialized cell-internal defect detection mechanism that analyzes waveform discrepancies at cell ports. This segmentation allows each part to be optimized independently, maintaining simplicity where possible while adding complexity only where necessary for detecting cell-internal defects.
Solution Approach 2:
The patent introduces waveform comparison as an intermediary mechanism between the test pattern application and defect detection. By capturing and comparing waveforms at cell ports during simulation, the system can detect cell-internal defects without directly modeling them, using the waveform differences as indirect evidence of internal faults.
2Productivity
If gate models are used for injecting faults at cell ports, then the ATPG process is efficient and works at high-level circuit design, but real layout-based defects inside library cells cannot be modeled
Solution Approach 1:
The patent creates a copy of the circuit design at the gate level for ATPG purposes, while simultaneously using the available layout information to identify potential cell-internal defect locations. This allows the efficient gate-level ATPG process to continue while adding defect detection capability through waveform analysis, without requiring a complete redesign at the layout level.
Solution Approach 2:
The patent changes the detection parameter from direct fault injection (which requires detailed layout modeling) to waveform discrepancy analysis at cell ports. This parameter change allows the use of standard gate models for efficient ATPG while detecting cell-internal defects through their electrical effects on port waveforms, bridging the gap between efficiency and precision.
3Ease of operation
If no faults within library cells are assumed, then the standard ATPG process remains simple and fast, but cell-internal defects go undetected
Solution Approach 1:
The patent implements a self-service defect detection mechanism where the ATPG process itself generates the data needed for defect detection. By capturing waveforms during the normal ATPG simulation and comparing them against expected behavior, the system detects cell-internal defects using the same test patterns and simulation infrastructure already in place, without requiring separate detection processes.
Data Source
AI summary
A method of identifying cell-internal defects: obtaining a circuit design of an integrated circuit, the circuit design including netlists of one or more cells coupled to one another; identifying the netlist corresponding to one of the one or more cells; injecting a defect to one of a plurality of circuit elements and one or more interconnects of the cell; retrieving a first current waveform at a location of the cell where the defect is injected by applying excitations to inputs of the cell; retrieving, without the defect injected, a second current waveform at the location of the cell by applying the same excitations to the inputs of the cell; and selectively annotating, based on the first current waveform and the second current waveform, an input/output table of the cell with the defect.