Role of acidic and alkaline cleaning solutions on ceria removal and brush-mediated cross-contamination during post-STI CMP cleaning

Ceria-based slurries used for shallow trench isolation (STI) chemical mechanical planarization (CMP) leave residual particles that must be effectively removed during post-CMP cleaning to prevent wafer defects and cross-contamination. Although polyvinyl acetal (PVAc) brush scrubbing is widely used for ceria removal, particles retained within the brush may be transferred to subsequent wafers. This study systematically investigated the influence of alkaline standard clean-1 (SC1, NH 4 OH:H 2 O 2 :deionized water = 1:4:20, pH ≈ 12) and acidic dilute hydrofluoric acid (DHF, 0.9 wt%, pH ≈ 2) on ceria removal, brush contamination, and particle transfer on tetraethyl orthosilicate (TEOS) and silicon nitride (SiN) wafers. Full-wafer particle mapping demonstrated that SC1 achieved a higher cleaning efficiency than DHF did, resulting in lower detected particle-like defect counts. SC1 resulted in lower brush Ce accumulation than did DHF. Under DHF cleaning, the loaded brush results supported brush-mediated particle transfer on TEOS, whereas the substantial fresh brush defect response on SiN prevented direct attribution of the SiN defects to ceria cross-contamination. Inductively coupled plasma–mass spectrometry (ICP-MS) measurements revealed higher Ce concentrations in digests of DHF-treated brushes (1.3–5.4 ppb) than of SC1-treated brushes (0.25–1.1 ppb). Together with zeta potential and XDLVO (extended Derjaguin–Landau–Verwey–Overbeek) analyses, the experimental results suggest that particle retention and release are influenced by the combined effects of interfacial interactions and brush–wafer contact mechanics, identifying cleaning chemistry as a major factor controlling cross-contamination during post-STI CMP cleaning.