Reduction and Optimization of Point-of-Use Abatement Wastewater
Adam Stover, Angela Bayler, Kevin Luc
Wastewater generation of high-volume manufacturing (HVM) semiconductor wafer fabs is becoming an increasingly important topic for not only sustainability but also for long-term cost management. Wastewater needs to be processed before discharge, which has a fixed cost per volume of water. Furthermore, on-site treatment plants have a fixed capacity and any expansion can be a costly capital project. There are several sources of wastewater for semiconductor HVM, including point-of-use (POU) abatement and chemical mechanical planarization (CMP) effluent. As HF comprises more than 40% of the chemical waste from a typical HVM fab , this paper will focus on both sources and effluent minimization strategies. HF is not only a process gas but also a byproduct of PFC (CF4, CHF3, etc.) destruction in a POU abatement system. Typically, a burn/wet POU abatement system will react the PFC gas to HF and CO2 in the first stage and then capture the acid byproducts in the subsequent wet scrubber. However, the POU abatement must cycle fresh water through the system and discharge HF waste to manage the pH to both protect the abatement system components as well as ensure appropriate removal of the HF species. This paper will give a quick overview of POU burn/wet abatement process and chemistry-specific factors to consider around wastewater generation. After the introduction, specific wastewater optimization strategies will be discussed including signal-based water usage, real-time pH measurement, and POU caustic (KOH or NaOH) dosing. Finally, a best-known method (BKM) state that incorporates both pH and caustic flow to reduce wastewater based on KF and NaF solubility limits is discussed in detail with example process recipes.