HIGH-PERFORMANCE LITHOGRAPHY WITH ADVANCED MODIFIED ILLUMINATION

A modified illumination technique recently developed is known to impro ve the resolution and DOF (depth of focus) dramatically. But, it requi res substantial modification in optical projection system and has some problems such as low throughput caused by low intensity and poor unif ormity. And it is very difficult to adjust illumination source accordi ng to pattern changes. To solve these problems, we developed a new ill umination technique, named ATOM (Advanced Titled illumination On Mask) which applies the same concept as quadrupole illumination technique b ut gives many advantages over conventional techniques. This newly inse rted mask gives drastic improvements in many areas such as DOF, resolu tion, low illumination intensity loss, and uniformity. In our experime nts, we obtained best resolution of 0.28 mum and 2.0 mum DOF for 0.36 mum feature sizes with i-line stepper, which is two times as wide as t hat of conventional illumination technique. We also obtained 0.22 mum resolution and 2.0 mum DOF for 0.28 mum with 0.45 NA KrF excimer laser stepper. For complex device patterns, more than 1.5 times wider DOF c ould be obtained compared to conventional illumination technique. From these results, we can conclude that 2nd generation of 64 M DRAM with 0.3 mum design rule can be printed with this technology combined with high NA (>0.5) i-line steppers. With KrF excimer laser stepper, 256 M DRAM can be printed with wide DOF.