Double Patterning for 56 nm Pitch Test Designs Using Inverse Lithography

The ITRS roadmap(1) lists double patterning 193 nm immersion exposure with inverse lithography as the likely solution through the 22 nm half pitch generation. Three different patterns, scaled to 56 nm pitch, were explored using inverse lithography.(2,3) The patterns are a trim mask design adapted from Schenker, et al.(4), a bit line design published by Pyo, et al.(5) and a metal layer design published by Lucas, et al.(6). A free form gray scale illuminator was determined for each pattern. Good results were obtained for the trim mask design with a process variation of less than 8 nm for 50 nm of defocus and MEEF less than 6. The bit line design had to be modified from the published version which increased the pattern area by 18.8%. For this pattern there was a maximum process variation of 11 nm for 50 nm of defocus and MEEF less than 14. The metal layer design had to be modified which increased the pattern area by 2.6%. With these changes there was a maximum process variation of 8.4 nm for 50 nm of defocus and MEEF less than 7.