In lithography employed in IC fabrication, focus and exposure directly determine the printed resist image. Focus and exposure settings may be optimized with a focus exposure matrix (FEM) in which one parameter is varied by column and the other parameter is varied by row. A focus exposure matrix should be measured on a highly accurate and precise metrology tool, such as a CD-SEM. This experiment was performed using a Canon FPA 2000-i1 stepper, an SSI 150 coat/develop track, and a Hitachi S-6780 CD SEM. ProData was used to graphically analyze the numerical data collected on the CD-SEM. Data collected in this experiment shows that, for the given equipment, varying exposure from 120 to 200 mJ/cm2 in 10 mJ/cm2 increments and focus from —0.5 to +1.5 microns in 0.25 micron increments gives a CD range beyond the +/-l0% needed.
Burkholder, Jason L.
"Lithographic Process Evaluation by CD-SEM,"
Journal of the Microelectronic Engineering Conference: Vol. 10
, Article 2.
Available at: http://scholarworks.rit.edu/ritamec/vol10/iss1/2