Flat-top femtosecond laser modification enhances chemical mechanical polishing of 4H-SiC through progressive removal of laser-induced periodic surface structures (LIPSS)

The high hardness and chemical inertness of silicon carbide (SiC) hinder efficient planarization by chemical mechanical polishing (CMP). Femtosecond laser modification can enhance CMP by generating laser-induced periodic surface structures (LIPSS). However, the role of LIPSS in CMP material removal and how LIPSS are removed during polishing remain unclear. In this study, flat-top femtosecond laser modification was applied to 4H-SiC. LIPSS formation was examined by surface characterization, thermal evolution was analyzed using extended two-temperature model (eTTM) simulations, and LIPSS removal was tracked at successive CMP stages. The results showed that beam shaping did not alter the LIPSS types formed, but the flat-top beam produced a more uniform and stable LIPSS distribution. Lower scanning speeds produced stronger heat accumulation in the eTTM simulations and a transition from LSFL-dominated to HSFL-dominated morphologies in the experiments. Compared with untreated 4H-SiC, all LIPSS surfaces exhibited higher initial material removal rates (MRRs) and 23.33–41.67% greater cumulative material removal after 3 h of CMP. During the initial CMP stage, elevated surface regions and LIPSS ridges were preferentially flattened, expanding the continuous polishing plane. As CMP proceeded, residual LIPSS below the polishing plane were progressively exposed and removed, while the measured MRRs gradually approached the value for untreated 4H-SiC. These results provide a stage-resolved description of LIPSS removal and polishing-plane evolution during CMP, clarifying how LIPSS contribute to the transient enhancement of material removal.