Chrome-less mask inspection method

A method of inspecting a chrome-less mask, wherein the chrome-less mask at least includes a transparent region and a phase shift region, the method comprising the steps of:

• providing a database holding:
• a first mask database corresponding to the chrome-less mask, wherein the first mask database further includes a phase shift pattern and that area and pattern of the phase shift pattern corresponds with area and pattern of the chrome-less mask;
• a second mask database, wherein the second mask database further includes a frame line pattern and that area and pattern of the frame line pattern is identical to the area and pattern of the phase shift pattern of the first mask database;
• and
• a first inspection signal pattern, wherein the first inspection signal pattern is generated by the second mask database;
• providing an inspection instrument for inspecting the chrome-less mask and a second inspection signal pattern for inspecting the chrome-less mask, wherein the scanning location of the second inspection signal pattern corresponds to the scanning location of the first inspection signal pattern;
• and
• comparing the first inspection signal with the second inspection signal to find any difference, wherein no discrepancies between the first inspection signal pattern and the second inspection signal pattern indicates the chrome-less mask is defect-free.