Optimization of lithography process to improve image deformation of contact hole sub-90 nm technology node

In resolution limited lithography process, the image deformation is getting severer. This is very important area where we need to fully understand and improved since the image deformation is directly giving poor CD control effect. Especially, contact hole image will be more sensitive since it has lower k1 factor that line and spaced pattern. This image deformation of contact hole can give some severe electrical fail due to not opened contact. In our case, we observed some critical failure mode of diagonal induced by abnormal contact hole shape of rough edge. In this paper, we investigate how deformed contact hole image impacted on degradation of device performance in electrical properties and yield and how we can improve it. To quantitatively analyze image deformation of contact hole, we recommend new measurement method first. This new measurement gives exact image deformation amount at different experimental conditions. Finally, we will show how experimental conditions such as soft bake temperature, post expose bake temperature, hardening bake temperature, illumination condition and mask bias change image deformation of contact hole.