Gas abatement: environmental drivers and constraints

Gas abatement is critical for the semiconductor industry to meet emissions regulations. The chip manufacturing process uses high quantities of a diverse mixture of gases for wafer deposition, but the gases may not be entirely consumed, or gaseous by-products may be generated in processing or abatement chambers. Such gases may be hazardous, pyrophoric, toxic or otherwise harmful to the environment or public health. Several factors contribute to gas abatement becoming an increasingly important topic of conversation for the semiconductor industry: 
1. Air emissions limits are tightening in some regions, creating new demand for gas abatement technology Gas abatement systems are becoming progressively more standard across the industry, but the rate of adoption is subject to regional discharge requirements. Josh McCrory observed that a recent priority for semiconductor manufacturers is the continuous lowering of emissions for nitrogen oxides (NOx), especially in regions with strict NOx limits, such as Germany and the US. NOx are byproducts from wafer deposition processes which use nitrous oxide, ammonia and process nitrogen sources, which are a particularly difficult gases to abate.
2. Water usage and energy usage can be high in gas abatement systems Burn/wet point-of-use gas abatement is one of the most frequently adopted methods. McCrory explained that the first stage in this technique involves cracking the gases into less harmful compounds, which requires maintaining elevated temperatures to enable the necessary chemical reactions. Energy consumption and technological difficulties in maintaining such temperatures are both challenges for consideration. Adam Stover explained that abatement systems also generate a high quantity of wastewater, accounting for probably 50% or more of wastewater volumes at some fabs, depending on the type and age of the abatement system. This is because water is required in the wet scrubber to entrap particulate contamination that could otherwise cause smog in the atmosphere. Water is also used to flush abatement systems to increase the pH of acidic gas to prevent corrosion in abatement system infrastructure.
3. The ever-increasing complexity of the semiconductor manufacturing process affects gas abatement systems As manufacturing complexity increases, a more diverse mixture and greater quantity of gases are generated as by-products of the chip-making process. Stover explained that greater flows of acidic gases are problematic for gas abatement infrastructure, as there is greater potential for corrosion of system components. Moreover, greater quantities of water may be needed to counteract acidity, meaning increased gas flow can place pressure on wastewater treatment infrastructure. Some methods are available to address these challenges. Stover said that dosing acidic waste gas inside the abatement system with alkaline chemicals – such as sodium fluoride or potassium fluoride – is a standard practice in Europe, but slowly emerging in the US. Neutralizing the acid in such a way can prevent corrosion to critical components and, in turn, avoid maintenance costs and downtime. Furthermore, the method minimizes the water flow required in the gas abatement system and reduces wastewater generation, therefore reducing energy requirements for water treatment. Stover explained that return-on-investment is the critical factor in determining the rate of adoption of this approach, but fabs in water-stressed areas may find such a method beneficial. McCrory agreed that there has been a recent uptake in chip manufacturers wanting to close the loops in their gas abatement systems by recycling more water and reducing wastewater discharge. He also observed that chip manufacturers want to reduce energy consumption, which can be done by digitally connecting the process tool using the gas with the abatement technology. By doing so, the gas treatment technology can be run at idle modes or different burner intensities according to the gas and type produced.