Ammoniacal nitrogen is one of the new parameters incorporated under the Industrial Effluents Regulation in Environmental Quality Act (EQA) starting from January 1st, 2010. Under this regulation, ammoniacal nitrogen limit for industries is regulated at a maximum limit of 10 ppm and 20 ppm depending on whether the facilities located upstream or downstream of the water catchments area. However, the ammoniacal nitrogen limit for semi-conductor companies that started their operation before 2010 has been increased to twice the initial limit due to concerns raised by some of the affected companies. This temporary limit was loosened until January 1st, 2020. The ammoniacal nitrogen is contributed by the use of ammonium hydroxide solution in the wafer fabrication industry, particularly in Chemical Mechanical Polishing (CMP) process. In CMP, the surface of silicon wafers being polished with slurry causing deposition of debris on the wafers. The cleaning process after polishing is termed as a post-CMP step. This paper focuses on the evaluation of post-CMP cleaning efficiency using a SpeedFam IPEC (SFI) AvantGaard™ 776 polisher tool. There are two stages of post-CMP steps named as buffing and scrubbing process. There were studies conducted by past researchers on post-CMP cleaning but none of these studies can be adopted either because the techniques were not economical for production scale compared to wet cleaning process or the chemicals selected are ammonia-based. The objective of the study is to analyse cleaning efficiency at both buffing and scrubbing steps and formulate an alternative solution that does not contain ammonia without compromising cleaning efficiency. It was discovered that the particles on the wafers were effectively removed with efficiency removal of 99% during the buffing step and the special formulated acid named SilTerra Cleaning Solution (SCS) provides comparable capability with ammonium hydroxide on particles and metallic in which both achieved cations and anions removal efficiency higher than 97%. The unique formulation of SCS contains hydrogen peroxide, sulphuric acid, and an additive. The chemical is proprietary of SilTerra by four inventors including the corresponding author. SCS was selected for this evaluation since it contains necessary ingredients to oxidize and dissolve the contaminants. The attempt to skip the application of chemicals during post CMP scrubbing was not promising as anions removal efficiency yielded lower than 95% removal efficiency.
