Comparison of the applications of process simulations and FMEA: two case studies

In manufacturing it is imperative to control defect densities and film properties within unit process modules. Often, however, a lack of detailed characterization on cutting edge processes can hinder effective troubleshooting when problems do occur. We intend to highlight simple problem solving methodologies such as the Failure Modes and Effects Analysis (FMEA) that can be applied to a wide range of everyday problems that occur on all process modules. We provide two real life cases where the advanced and complex Finite Element Modeling (FEM) of the Navier Stokes Equation and the FMEA yielded identical results. The first case is that of contamination to the wafer backside that occurred in a CVD tungsten system and resulted in depressed yield, and equipment downtime in all downstream process modules. Process simulations at different settings of gas flow rates and pressure identified a process window where wafer backside contamination could occur. Subsequently an FMEA yielded identical results for the root cause. Within this case we present all possible failure mechanisms, review the methodologies used for risk assessment analysis, material dispositioning criteria and explain the procedures put in place to detect and eliminate future backside contamination. In the second case we report analysis of excessive downtime due to poor film uniformity that occurred from upgrading a CVD tool from 6" to 8". The differences between the 6" and the 8" chambers were analyzed using process modeling and FMEA