New method of tilted illumination using grating mask: advanced tilted illumination on mask

摘要

A modified illumination method recently developed is known to improve resolution and depth of focus (DOF) dramatically. But, it requires substantial modification in the optical projection system and has some problems such as low throughput caused by low intensity and poor uniformity. To solve these problems, we developed a new illumination technique, named advanced tilted illumination on mask (ATOM) using phase grating which is the same, in principle, as quadrupole illumination but a very simple approach with little loss of intensity. In our experiments, we obtained the best resolution of 0.28 $mu@m and 2.0 $mu@m DOF for 0.36 $mu@m feature size with an i-line stepper, which is two times as wide as that of a conventional illumination method. We also obtained 0.22 $mu@m resolution and 2.0 $mu@m DOF for 0.28 $mu@m with an 0.45 NA KrF excimer laser stepper. For complex device patterns, a more than 1.5 times wider DOF could be obtained compared to the conventional illumination method. From these results, we conclude that second generation of 64 M DRAM with 0.30 $mu@m design rule could be printed well with this technology combined with high NA ($GRT 0.5) i-line steppers. With a KrF excimer laser stepper, a 256 M DRAM with a 0.25 $mu@m design rule can be printed with the wide DOF.