The Role of Process Hazard Assessment in Semiconductor Process Development
Process Hazard Assessment (PHA) is developed by IMEC as a tool used to predict the ESH-impact of new semiconductor processes that are being investigated. The PHA is based upon a “process window “which is detailed in a Process Definition Sheet (PDS). The PDS gives maximum and estimated process flows as well as the physical conditions (temperature, pressure) of the process. The first step of the PHA is a Multi Criteria Hazard Assessment aiming to evaluate the physical hazards, toxicological effects as well as an evaluation of standards and regulations that apply to the use of the aimed precursors. The process recipe and stoechiometry allows us to investigate the chemical reactivity or physical effects of by-products. Effects of exothermal or endothermal reactions, built-up of solids, or release of explosive reaction products are assessed during this second stage of the PHA. If the reaction mechanisms are unknown the effects are investigated in an experimental way by monitoring the physical effects and by chemical analysis such as GCMS, FTIR,…while ramping-up the process from diluted chemicals and starting from benign process conditions. The outcome of the PHA allows one to select the technical and organizational measures to further develop or demonstrate the process under safe conditions. Segregation of drains and exhausts, installation of on-board fire extinguishing systems on tools, use of process diluents, adequate effluent abatement or the change of process precursors can be the result of a PHA. Also, the advantage of running a PHA in a systematical way lies in educating scientists in the ESH-effects of the products and process conditions that they select for process development, hence in safe and sustainable processes that can be transferred to the semiconductor manufacturers.