Focus control system

A process for forming focus setting targets on a semiconductor wafer and controlling focus parameters in a lithographic process used in manufacture of functional microelectronic circuit elements comprising:

• providing a lithographic mask having a target mask comprising first and second target mask portions, the first target mask portion comprising a plurality of opaque, spaced element shapes having essentially the same length and width and forming an array, the second target mask portion comprising a plurality of transparent, spaced element spaces having essentially the same length and width and forming an array, ends of the individual elements in each target portion being aligned to form first and second opposing array edges, the array elements having a predefined pitch, the width between the array edges being sensitive to defocus when printed on a substrate;
• projecting an energy beam through the target mask portion onto a first location of a substrate at a first focus setting;
• lithographically forming a first target on the substrate corresponding to the target mask at a first focus setting, the first target having complementary, tone reversed target array portions containing a measurable width between the target array edges sensitive to defocus;
• projecting an energy beam through the target mask portion onto a second location of the substrate at a second focus setting;
• lithographically forming a second target on the substrate corresponding to the target mask at a second focus setting, the second target having complementary, tone reversed target array portions containing a measurable width between the target array edges sensitive to defocus;
• measuring the width between the target array edges for each of the first and second targets on the substrate and comparing the target array edge width of the first and second targets;
• determining a desired focus setting of the energy beam based on the comparison of the dimensions of the first and second target array widths;
• and
• using the determination of the desired focus setting of the energy beam to correct energy beam focus during lithographic forming of the functional circuit elements.