Pattern inspection of etched multilayer extreme ultraviolet mask

Abstract

Abstract. Patterned mask inspection for an etched multilayer (ML) extreme ultraviolet mask was investigated. In order to optimize the mask structure from the standpoint of a pattern inspection the mask structure not only from the standpoint of a pattern inspection by using a projection electron microscope but also by using a projection electron microscope but also by considering the other fabrication processes using electron beam techniques such as critical dimension metrology and mask repair, we employed a conductive layer between the ML and substrate. By measuring the secondary electron emission coefficients of the candidate materials for the conductive layer, we evaluated the image contrast and the influence of the charging effect. In the cases of 40-pair ML, 16-nm-sized extrusion and intrusion defects were found to be detectable more than 10 sigma in half pitch 44, 40, and 32 nm line-and-space patterns. Reducing 40-pair ML to 20-pair ML degraded the image contrast and the defect detectability. However, by selecting B 4 C as a conductive layer, 16-nm-sized defects and etching residues remained detectable. The 16-nm-sized defects were also detected after the etched part was refilled with Si. A double-layer structure with 2.5-nm-thick B 4 C on metal film used as a conductive layer was found to have sufficient conductivity and also was found to be free from the surface charging effect and influence of native oxide. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Investigation of defect detectability for extreme ultraviolet patterned mask using two types of high-throughput electron-beam inspection systems

“…1,27 On the other hand, in the EB inspection system, the secondary electron emission coefficient (SEEC) determines the material contrast on the SE image. 9,19,21,23 The SEEC of the absorber is larger than that of the ML. Therefore, the bright and dark areas in the EB image correspond to the absorber and ML parts as shown in Fig.…”

“…4. 9,21,23 The intensity profile of a pinhole defect is much weaker than that of the ML level. This is because the SEs from the bottom of the pinhole are blocked by the side walls of the defect.…”

“…2. 9,19,21,23,27 The defect image contrast is also influenced by the defect size and shape. In the cases of pinhole and intrusion defects, as the defects become smaller, the signals from the ML become lower in both cases of DUV and EB images.…”

“…9,22,24 It was also found that the optimal inspection conditions, such as landing energy, depend on defect size and shape. 9,21,23 In this paper, in order to investigate the nature of defect detectability of an EUV patterned mask using an EB inspection system, the impacts of defect size and shape, and of the line edge roughness (LER), the image processing algorithm on detectability are analyzed using the PEM and SEM inspection systems. Figure 1 shows schematic illustrations of the PEM and SEM inspection systems.…”

“…9,[14][15][16][17][18][19][20][21][22][23][24] In order to accelerate this development program, the optimal inspection condition and the analysis of PEM image were investigated by using a computer simulation. 9,[18][19][20][21][22][23] We had already reported that a ≥12-nm-sized defect on hp 64-nm mask pattern was detectable by the developed PEM, 24 and that the detectability is in good agreement with the simulation results. 9,22,24 It was also found that the optimal inspection conditions, such as landing energy, depend on defect size and shape.…”