RF power window for O₂ plasma pre-stripping of thick AZ P4620 on ultrathin DLCCoated AlTiC

Diamond-like carbon (DLC) coatings are widely used as ultrathin protective overcoats in hard disk drive (HDD) slider fabrication. During manufacturing, thick photoresist (PR) layers are typically removed by wet isopropanol-based Isopropanol Rinse cleaning (IRC). However, incomplete dissolution of thick PR can lead to persistent nanoscale contamination on the DLC surface. To improve wet-clean compatibility, oxygen plasma treatment can be employed as a controlled pre-stripping step to partially degrade the resist prior to IRC removal. Nevertheless, plasma conditions sufficient for PR thinning may overlap with ion-energy regimes capable of inducing structural modification of nanometer-scale DLC films. In this work, the RF power window for O₂ plasma pre-stripping of thick AZ P4620 photoresist while limiting plasma-induced modification of the ultrathin DLC overcoat on AlTiC was systematically investigated over a wide power range (10–600 W). Surface morphology and roughness were characterized by SEM and AFM, while chemical and fragment evolution were examined by ToF-SIMS. Three distinct regimes were identified. At low RF power (10–100 W), insufficient photoresist degradation resulted in persistent hydrocarbon fragments and minimal surface roughness evolution (Ra ≈ 0.45 nm). At intermediate RF power (300–400 W), effective photoresist thinning was achieved while maintaining only moderate DLC surface modification, with Ra increasing to approximately 0.82 nm. At high RF power (500–600 W), pronounced roughening and the appearance of oxygen-related interfacial species were observed, accompanied by a sharp increase in roughness (Ra ≈ 1.75 nm), suggesting behavior consistent with ion-assisted near-surface modification of the ultrathin DLC layer. These results identify 300–400 W as the optimum RF power window for hybrid dry–wet cleaning, enabling effective resist conditioning while limiting plasma-induced modification of the underlying DLC coating. The results define a transition boundary between plasma-assisted resist conditioning and ion-driven DLC modification. Within this regime, improved IRC compatibility is achieved while restricting severe DLC surface degradation, as inferred from combined SEM, AFM, ToF-SIMS, and SEM–EDX analyses. These findings provide practical guidance for integrated dry–wet cleaning strategies in DLC-protected systems.