Chemical mechanical polishing of stainless steel foil as flexible substrate

Stainless steel foils as thin as 120 μm are polished to meet the requirement of low roughness for fabricating flexible thin-film transistors on them used in display or sensor. Using the colloidal silica as abrasives in the chemical mechanical polishing (CMP) procedure, different slurries are evaluated in terms of material removal rates (MRRs). Preliminary CMP tests show that the slurries containing oxidant with the pH less than 2.0 produce the greatest removal rate, and accordingly the mechanism of material removal is proposed. The surface topography of stainless steel before and after polishing is characterized by optical image, scanning electron microscopy and atomic force microscopy image. The surface roughness can be reduced from the unpolished 13.6 nm to the polished 0.7 nm. However, itʹs found that the microscopic defects of 1–2 μm in size are always present within the polished surface, and the electrochemical cause of their occurrence is suggested according to elementary mapping analysis.