Post cleaning experiments for front end of the line (FEOL) CMP with silica and ceria slurries are carried out on commercial polishers with 300 mm oxide, nitride, and integrated shallow trench isolation (STI) wafers. Considering the charge attraction or repulsion between particles and wafer surface, both acidic and basic clean chemicals are applied at different stages in the post CMP process sequence. Diluted hydrogen peroxide in a non-contact megasonic cleaner is used to remove ceria abrasive particles and polish residues with high efficiency. On-platen buff clean with or without pad conditioning can make an impact on the post CMP cleaning performance. Post CMP cleaning splits are executed in order to evaluate the effectiveness of each of the process steps and their roles in the overall cleaning performance. Silica-based slurries are usually adopted for bulk oxide polish while ceria-based slurries are more suited for the final "buff" polish where high selectivity is required. The ever stringent requirements for scratch reduction lead to the trend of adopting nano-sized (< 60 nm) abrasive particles in all types of CMP slurries. However, the higher surface charges per area of these nanoparticles and the resulting stronger adhesion force between them and wafer surface necessitates the modification of the chemistry and optimization of post CMP (pCMP) cleaning process to meet the low defect requirement.Between silica and ceria abrasive particles, the latter are heavier in weight and irregular in shape (as opposed to circular like silica), and hence may present more challenges for pCMP cleaning from weight and geometry point of view. However, atomic force microscope (AFM) measurement suggests that the adhesion force of irregular ceria is much lower than that of spherical silica on the surface of TEOS oxide, SiN x , and poly-Si in both acidic and basic pH regimes.1 Unlike silica, ceria exhibit redox reactions on SiO x surface, which should be taken into account when selecting the chemicals for pCMP cleaning. Meanwhile, besides silica and ceria abrasive particles, a robust FEOL pCMP clean process need to remove organic additives from slurry itself; by-products or polish residues (PR) such as SiO x , SiN x , and poly-Si from the wafer; and debris from CMP consumables such as pad (PU, polyurethane), carrier (stainless steel), retaining ring (e.g., polyether ether ketone, PEEK), and roller brush (polyvinyl alcohol, PVA).The selection of proper chemicals is often the first step toward pCMP cleaning. However, design of cleaning sequence, exploitation of the tool hardware, and optimization of process parameters are equally critical to achieve maximum cleaning efficiency.2 During the final ("buff") polish step, for example, the use of hard vs. soft pads, in-situ vs. ex-situ conditioning, and pad rinse with DIW vs. clean chemical can all modulate defect generation to various degrees, and hence affect the overall post cleaning performance. In the post CMP clean module, cleaning with or without mechanical contact, brush or "penci...
