Repairing Ta absorber x-ray masks with gas-assisted focused-ion-beam etching

A process using gas-assisted etching (GAE) was developed to repair defects in x-ray masks with a high aspect ratio Ta pattern. XeF2 was employed as the etchant gas. To control the adhesion of XeF2 gas molecules on the surface of a sample, we adjusted the gap between the point of the nozzle and the sample surface. The sidewall of the pattern was vertical, and rounding at the pattern top was not seen. The linewidth of the pattern was in good agreement (within 0.02 micrometer) with the setting width. The pattern had a very smooth bottom due to the chemical effect of etching. In examining the printability by printing on a resist using the SR exposure system with a repaired mask, we confirmed that a Ta absorber x-ray mask could be repaired with high accuracy by GAE.