A method includes performing a beam scan on a photolithography mask to repair the photolithography mask. After the beam scan, a radiation treatment is performed on the photolithography mask. The method is performed by an apparatus including a beam generator configured to generate and project a beam on the lithography mask, a radiation source configured to generate a radiation on the lithography mask, and a process gas source configured to release a process gas onto the lithography mask. The process as reacts with a surface portion of the lithography mask to repair the lithography mask. With the radiation treatment, residue process gas on the lithography mask is removed.