Soft failures are among the most challenging yield detractors. They typically show test parameter sensitive characteristics, which would pass under certain test conditions but fail under other conditions. Conductive-atomic force microscopy (CAFM) emerged as an ideal solution for soft failure analysis that can balance the time and thoroughness. By inserting CAFM into the soft failure analysis flow, success rate of such type of analysis can be significantly enhanced. In this paper, a logic chain soft failure and a SRAM local bitline soft failure are used as examples to illustrate how this failure analysis methodology provides a powerful and efficient solution for soft failure analysis.
With increasing complexity involved in advance node semiconductor process development, dependability on parametric test structures has also increased significantly. Test structures play a predominant role throughout the entire development cycle of a product. They are used to understand the process windows and also help to monitor the health of a line. This work provides a process flow sheet for root cause identification on chain opens on advanced 20 nm and sub-20 nm technologies setting a standard guideline for a specific category fail type. It provides a consistent way of attack in a much more streamlined fashion. Further, dependability on TEM rather than convention FIB cross-sections provides shortest time to root cause identification. Three typical cases encountered are discussed to demonstrate the idea: embedded chain opens by electron beam absorbed current (EBAC) isolation, chains opens at level by EBAC isolation, and chains opens at level by passive voltage contrast isolation.
Conductive thin film residues often referred to as puddles could be challenging fails to detect. A large extant film with no distinct boundaries would make the task more challenging for a comparison between good and bad region. Advanced node 20nm and 14nm technologies mandate use of several conductive thin films in the front end of line processes, and hence a potential for high defects during initial product development stage. Use of other electrical characterization techniques in combination with scanning electron microscopy inspection will be a very powerful tool to detect the root cause affirmatively. Cross-sectional images are necessary to understand the root cause of the fails for corrective actions. This work uses three cases of power supply shorts as a platform to demonstrate the idea, demonstrating a few situations where traditional techniques might reach its limits while the authors depend on additional characterization tools to confidently detect and confirm fails.
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