Single exposure EUV patterning optimization and defect inspection of hexagonal contact hole arrays using voltage contrast metrology

Abstract

A single exposure EUV patterning process has been optimized for hexagonal contact holes (CHs) at pitch 36 nm and SRAM via. Defect inspection results are reported using after etch voltage contrast (VC) metrology as well as after metallization. By comparing top-down scanning electron microscopy (SEM) and VC images, the VC technique was proven to detect the close defective CHs not only on the top surface but also at the bottom of CHs. This is confirmed on cross section inspection using transmission electron microscopy (TEM) metrology. To quantify the number of defects (NoDs) per million CHs, both a greyscale analysis and a computer vision-based defect analysis algorithm are used and exhibits the dependence of NoDs on CHs mean CD. This algorithm is capable of detecting, classifying, and incrementally counting the occurrence of defect instances as closed, partially open and open CHs. An advantage of this algorithm is its distortion invariance and independence from GDS alignment.