Correction of pattern-dependent errors in a particle beam lithography system

A method of forming, in a particle beam system, a mask for integrated circuit fabrication by operating on a set of input design data to produce a set of beam control data comprising the steps of:

• generating, in a data processing operation and in response to a first member of said set of input design data, a corresponding first member of said set of beam control data;
• sequentially repeating said step of generating until all members of said set of beam control data have been generated;
• and
• writing a mask pattern on a mask blank by directing said particle beam at said mask blank in accordance with said set of beam control data and transferring said mask pattern to said mask blank, further comprising the steps of:
• generating, in said data processing operation, an intermediate set of beam control data comprising a first subset containing corresponding members of said set of beam control data and a second subset comprising metrology beam control data;
• detecting when a location of an nth member of said set of input design data is within an area reserved for a metrology feature and substituting, in said intermediate set of beam control data, a corresponding member of a stored set of metrology beam control data for an nth member of said set of beam control data corresponding to said nth member of said set of input design data, whereby said intermediate set of beam control data comprises said first subset, comprising corresponding members of said set of beam control data, and said second subset, comprising corresponding members of said stored set of metrology beam control data;
• storing both said set of beam control data and said intermediate set of beam control data;
• writing a calibration pattern on a calibration mask blank by directing said particle beam at said calibration mask blank in accordance with said intermediate set of beam control data and transferring said calibration pattern to said calibration mask blank;
• measuring metrology features on said calibration mask blank to form a set of measured metrology data, forming a set of pattern correction data from said set of measured metrology data;
• writing a corrected mask pattern on a mask blank by directing said particle beam at said mask blank, in accordance with said set of beam control data corrected by said set of pattern correction data, and;
• transferring said corrected mask pattern to said mask blank.