As the design rule of wafer has been shrinking, the patterns on the mask also need to be getting smaller and even
smaller for some sub-resolution assist features, which makes mask inspection process need a high resolution (HR)
inspection systems. For this HR mask inspection, most mask inspector makers adopt a TDI(Time Delay & Integration)
sensor to enhance acquired image quality with the acceptable scan speed, thus, to minimize the inspection cost.
However, even TDI sensor may not get a sufficient gray level of pattern image for the most advanced mask patterns.
Furthermore, it might generate some false defects depending on the pattern shape and scan direction (in combination
with pattern direction). We manufactured two programmed defect masks (PDM); one is a ArF EPSM and another is a
EUV mask. By inspecting these masks with perpendicular scan directions, respectively, we evaluated the correlation
between scan direction and defect size/shape experimentally. We found that the inspection with the parallel direction to
pattern direction can increase the inspectability for the patterns and the defect sensitivity since this helps to enhance
signal to noise ratio from the TDI sensor. Our analysis can increase sensitivity of TDI sensor effectively without any
additional hardware modification.
Mask inspection plays a pivotal role in current high grade mask making processes and further its importance is getting bigger. The purpose of inspection process is as follows. One is simple sorting of NG masks that have fatal defects with high sensitivity. The other is improvement of total mask manufacturing process and mask quality using defect source analysis. As semiconductor device is getting shrunk down, the influence of mask defect is increasing. Therefore, there are special needs for the efficient use of such expensive inspection machines and the systematic approach of defect analysis. In this paper, we propose novel mask inspection flow to improve mask inspection capacity and systematic defect management. In general, Inspection process is divided by two steps. One is detection of defects and the other is review for defect analysis. Our concept of new inspection flow is adoption of individual defect review system after defect detection in inspection machine.
With this new inspection flow using defect review system, we could increase inspection capacity by 30% and set up unified defect analysis hub.