Scan Cell Modification for Intra Cell-Aware Scan Chain Diagnosis

Abstract

Conventional diagnosis methods are performed at the library cell level, which identify only defective cells. In reality, many defects affecting the inside of the cells cannot be identified, limiting yield improvement. To overcome the limit, cell-aware diagnosis has been introduced, but it is rarely used in scan chain domain due to the characteristics of a scan cell. Design of the scan cell is complex, but there are few I/O pins to control and observe. In this brief, the scan cell design is modified to observe more values inside the cell, distinguishing the many defect that could not be identified. Since the proposed method is not affected by logic and proceeds at the layout level of the scan cells, it is immune to type, size, or complexity of the circuit. Based on the layout data and some analog simulations, a new modified cell view for the intracell scan chain diagnosis is developed.