Extreme ultraviolet mask defect inspection with a half pitch 16-nm node using simulated projection electron microscope images

Susumu Iida,Hidehiro Watanabe,Ryoichi Hirano,Tsuyoshi Amano,Tsuneo Terasawa

doi:10.1117/1.jmm.12.2.023013

Abstract

According to an International Technology Roadmap for Semiconductors (ITRS-2012) update, the sensitivity requirement for an extreme ultraviolet (EUV) mask pattern inspection system is to be less than 18 nm for half pitch (hp) 16-nm node devices. The inspection sensitivity of extrusion and intrusion defects on hp 64-nm line-and-space patterned EUV mask were investigated using simulated projection electron microscope (PEM) images. The obtained defect images showed that the optimization of current density and image processing techniques were essential for the detection of defects. Extrusion and intrusion defects 16 nm in size were detected on images formed by 3000 electrons per pixel. The landing energy also greatly influenced the defect detection efficiency. These influences were different for extrusion and intrusion defects. These results were in good agreement with experimentally obtained yield curves of the mask materials and the elevation angles of the defects. These results suggest that the PEM technique has a potential to detect 16-nm size defects on an hp 64-nm patterned EUV mask.

Highlights

Extreme ultraviolet (EUV) lithography is a promising technique for a post-2 × -nm generation lithography
It is well known that improvement in image resolution can be realized by using an electron beam, as used in a scanning electron microscope (SEM)type inspection system, but because of the very small electron beam spot size used in such a system, it takes too much time for inspection
It should be noted that the 16-nm defect was detected in the case of 3000 electrons per pixel. This result indicates that the Downloaded From: https://www.spiedigitallibrary.org/journals/Journal-of-Micro/Nanolithography,MEMS,and-MOEMS on 23 Dec 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use optimization of current density and the image processing techniques are essential for defect detection

Summary

Introduction

Extreme ultraviolet (EUV) lithography is a promising technique for a post-2 × -nm generation lithography. We have been developing a projection electron microscope (PEM)[3] for pattern inspection, and we have evaluated its feasibility.[4,5,6] To accelerate this development program, a better understanding of image formation in PEM and improved prediction capability have become essential.[7] In recent times, the accuracy of simulations using advanced Monte Carlo methods has improved significantly These simulations take into account the charging and discharging effects, electromagnetic fields, detector configurations, and so on.[8,9,10,11,12] The simulated results are consistent with experimental results and can describe the physical phenomena of EUV mask imaging and metrology.[11,12] In this study, we describe defect detection using simulated PEM image by Monte Carlo simulation

Experimental

Simulated Inspection of Extrusion Defects and Effect of Image Processing

Secondary Electron Emission Coefficient of EUV Mask

Simulated Inspection of Intrusion Defects

Summary and Conclusions