Effect of pretreatment of high-dose implanted resists by activated hydrogen peroxide chemical systems for their effective removal by conventional sulfuric-peroxide mixtures

Stripping of photoresists (PRs) exposed to high-dose (>1E15 atoms/cm ²) ion beams is one of the most challenging steps in front-end-of-line (FEOL) processing. This is due to a refractory crust that forms on the resist surface during ion implantation. The objective of this paper is to investigate the use of hydrogen peroxide systems activated by metal ion or ultraviolet (UV) light for disrupting crust formed on deep UV resist to enable complete removal of crust as well as underlying PR. Systematic investigation of variables such as hydrogen peroxide and metal ion concentration and UV intensity has led to the development of an optimal formulation for attacking the crust. Optical microscopy, confocal microscopy, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy have been used to monitor the removal of the resist. A two-step process involving pretreatment with activated hydrogen peroxide solution followed by treatment with sulfuric acid-hydrogen peroxide mixture to remove crust and underlying resist has been developed.