Analysis of Pattern-dependent Rapid Thermal Annealing Effects on SRAM Design

Vidya Chhabria1 and Sachin S. Sapatnekar2
1Arizona State University, 2University of Minnesota


Rapid thermal annealing (RTA) is an important step in the semiconductor manufacturing process. RTA-induced variability due to differences in die layout patterns can significantly contribute to transistor parameter variations, resulting in degraded chip performance and yield. The die layout patterns that drive these variations are related to the distribution of the density of transistors (silicon) and shallow trench isolation (silicon dioxide) across the die, which result in emissivity variations that change the die surface temperature during annealing. While prior art has developed pattern-dependent simulators and provided mitigation techniques for digital design, it has failed to consider the impact of the temperature-dependent thermal conductivity of silicon on RTA effects and has not analyzed the effects on memory. This work develops a novel 3D transient pattern-dependent RTA simulation methodology that accounts for the dependence of the thermal conductivity of silicon on temperature. The simulator is used to both analyze the effects of RTA on memory performance and to propose mitigation strategies for a 7nm FinFET SRAM design. It is shown that RTA effects degrade read and write delays by 16% and 20% and read static noise margin (SNM) by 15% and the applied mitigation strategies can compensate for these degradations at the cost of a 16% increase in area for a 7.5% tolerance SNM margin.