12-inch Fabs Achieve TMAH Concentration Reduction Target of 2019 to Fulfill Green Manufacturing
Fulfilling circular economy to achieve zero impact on environment is a green manufacturing goal that TSMC has been bearing in mind. TSMC led the industry to build ”Tetramethylammonium hydroxide (TMAH) recycling system” in 2012, and took a further step to upgrade the system from high concentration recycling to low concentration comprehensive treatment in 2019.
With plenty of real tests in factories, TSMC successfully developed solutions to deal with various kind of process wastewater. TMAH average concentration at 12-inch fabs remained stable at below 8ppm, much better than 60ppm of the regulatory standard. The reduction of TMAH concentration reached 73% when the recycling system was established in 2012, achieving the sustainable target of 2019.
TSMC’s Refined Procedures of TMAH Treatment
TSMC has established the most rigorous wastewater classification management system in the semiconductor industry. It continues to improve the stability and efficiency of the system with thousands of parameter adjustments and resin category testing data every year. In 2019, TSMC further enhanced the management system, poured a large amount of facility manpower and time, and cooperated with Sanfu Chemical and Chang Chun Chemical to evaluate various kind of wastewater and resin features and analyzed the status of raw material use and waste discharge from equipment to find out the optimal treatment curve for all fabs through continuous testing, with the three major strategies for TMAH reduction : ”comprehensive collection”, ”refining for regeneration”, ”double treatment”.
Strategy One : Comprehensive Collection; Inclusion of Low-Concentration Equipment Scrubbing Water
In 2019, TSMC took a further step to collect and manage low-concentration liquid waste (TMAH<1,000 ppm). Instead of directly discharging the wastewater as before, pipelines for equipment scrubbing water were designed to recycle and manage the TMAH system in order to reclaim precious water resources.
Strategy Two : Refining for Regeneration Procedure; Reduce Regenerated Liquid Waste Concentration from Resin Towers
Cation resin towers are often used to adsorb TMAH in the industry. When the resin reaches saturation, strong acid is dosing to the tower for Ion exchange, so partner firms can collect the high concentration resin wastewater for recycling. However, the low concentration resin wastewater that can’t recycle becomes the main composition of TMAH in effluent. TSMC has repeatedly tested to reduce 90% of TMAH concentration by adding air-wash process, which uses air to inject to the resin tower for extrude wastewater to improve the efficiency of regeneration.
Strategy Three : Double Treatment; Recycle Regenerated Liquid Waste from Resin Towers
TMAH is regenerated during neutralization with strong acids. In the past, low-concentration TMAH acid could not be reabsorbed in the process due to sulfate ions (SO42-) and would often be discharged into wastewater. To resolve this issue, TSMC repeatedly examined and refined regeneration procedures until it successfully developed an anion resin tower mode, which takes regenerated liquid waste from resin towers and removes sulfate ions before introducing them into cation resin towers for effective absorption to further reduce TMAH concentration.
Moving Steadily towards Goal of Having Zero Impact on Environment
Currently all TSMC’s 12-inch fabs are almost at zero TMAH emission, and our next step is to optimize the systems at 8-inch fabs and backend packaging fabs. In order to get rid of photoresist from TMAH wastewater, TSMC works hard to test two-stage nano filtration (NF) technique that reduces the volume of reserve osmosis concentration. We expect to reduce 50% TMAH concentration through the experiment of nano filtration technique, so that all TSMC fabs can move towards the goal of having zero impact on environment.