Method for forming photomask

A method for forming a photomask, comprising:

• providing a photomask pattern according to a target pattern;
• simulating a first light intensity curve according to the photomask pattern;
• subjecting the first light intensity curve to a check on light intensities at pattern edges of the target pattern to define a light intensity error, wherein the light intensity error is a difference between the light intensities of the first light intensity curve corresponding to the pattern edges of the target pattern and a predefined standard light intensity;
• correcting the photomask pattern to reduce the light intensity error;
• identifying a lithography weak region in the target pattern;
• obtaining a second light intensity curve of the lithography weak region by simulation;
• subjecting the second light intensity curve to a check on peak light intensity to define a peak intensity error, wherein the peak intensity error is a difference between a peak value of the second light intensity curve and a predetermined peak value;
• retargeting the target pattern to reduce the peak intensity error;
• and
• re-correcting the photomask pattern according to the retargeted target pattern.