Method of approximating value of critical dimension of pattern formed by photolithography and method of fabricating photomask including opc based on approximated value of a cd of a pattern

A method of fabricating a photomask, the method comprising:

• providing a photomask having a mask pattern;
• patterning a film on a substrate using the photomask in a lithographic process to thereby form a film pattern bearing an image of at least one feature of the mask pattern;
• determining at least one value of the critical dimension (CD) of the film by scanning the film pattern with an electron beam of a scanning electron microscope (SEM);
• based at least in part on the at least one value of the CD determined using the SEM, approximating the value of the CD of the film pattern possessed by the film pattern at a point in time before the film pattern was irradiated by the electron beam of the SEM, whereby the approximated value of the CD of the film pattern is not influenced by any shrinkage of the film pattern caused by the electron beam;
• factoring the approximated value of the CD of the film pattern into an optical proximity effect correction (OPC) model;
• and
• altering a photomask, by changing a mask pattern thereof, based on the optical proximity effect correction (OPC) model into which the approximated value of the CD of the film pattern has been factored.

A method for use in fabricating a photomask, the method comprising:

• providing a photomask having a mask pattern;
• forming a photosensitive film pattern using the photomask and measuring a CD of the photosensitive film pattern at least one time using a scanning electron microscope (SEM);
• and
• predicting a value of the CD of the photosensitive film pattern, at a point in time before the CD of the film pattern has been altered by the SEM, using at least a value or values of the CD measured using the SEM.