Reliability Challenges and Inline Metrology - An Effective Approach to Implementation in Advanced Devices

As semiconductor devices scale down in size, the sensitivity of reliability to process variation increases. This increase is due to the high-reliability requirements for advanced system applications, the narrowing process margins, and the high sensitivity of devices to composition. At the process level, specific materials or process chambers can degrade the devices' reliability, induced by additional charge traps in the adjacent cells and poor data retention due to contamination by killer elements and complex structures, although they may be required from a process integration perspective. It is difficult to effectively detect killer elements during the process, which can create or accelerate reliability failure. Several killer elements cause reliability degradation: F (fluorine), CI (Chlorine), local strains in the SiGe layers, and plasma-induced traps at the gate oxide interfaces. We find that an effective approach to prevent reliability failure is to monitor potential killer elements in the process, maintain them under threshold levels and screen out heavily contaminated wafers before wafer fab-out. This paper addresses the relationship between specific killer elements and reliability and reviews the enablers of inline metrology that can prevent reliability failure by early detection and monitoring of variation of killer elements in fabs.