Impact of B₄C capping layer for extreme ultraviolet mask on the sensitivity of patterned mask inspection using a projection electron microscope

Abstract

Abstract. The inspection sensitivity of a patterned extreme ultraviolet mask with B 4 C-capped multilayer (ML) was investigated using a simulated projection electron microscope (PEM) image. Extrusion and intrusion defects with 16-nm size were detected with their intensity of >10 times the standard deviation of the background level on a half-pitch 64-nm line-and-space pattern. The defect detection sensitivity in this case was higher than that of a Ru-capped ML sample and has a potential to meet the requirement for beyond 16-nm node generation from the standpoint of patterned mask inspection using the PEM technique. These results indicate that the B 4 C capping layer, besides its good durability, has an advantage for high sensitivity of patterned mask inspection. The optimal condition of the incident beam energy was found to be 500 and 1,000 eV for the samples of B 4 C-capped ML and B 4 C-buffered Ru-capped ML, respectively. The sensitivity of defect detection was strongly affected by the difference of secondary electron emission coefficients (SEECs) between the absorber layer and capping layer. However, the small incident beam energy was found to be preferable when the SEEC difference was relatively high. © 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.…”

“…The detailed simulation conditions for PEM have been described in earlier reports. 9,[21][22] The difference between the simulated image with defects and that without defects is defined as the difference image. In order to enhance the defect signal intensities, different types of image processing operations for PEM and SEM images were applied to the simulated images.…”

“…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.…”