Multilayer bottom topography effect on actinic mask-blank inspection signal

Abstract

The detectability of a small phase defect on a multilayer-coated mask blank was investigated by using electromagnetic simulation. When a smoothing deposition of multilayer coating is used the inspection signal from the phase defects is characterized not only by a top surface topography of the multilayer but also by bottom topography. To understand the impact of the bottom topography we first calculated the phase shift of reflected EUV light from multilayers with various bi-layer thicknesses since the smoothing effect may be equivalent to the local multilayer thickness variation. Then, we estimated the actinic inspection signal intensity from bump, pit, line, and groove defects taking into account the phase shift due to bi-layer thickness change and the phase change due to the top surface topography. Simulation results revealed that the phase shift due to the top surface topography was enhanced by smoothing deposition for both convex and concave shaped phase defects. Thus the bump defect is detected as higher bump than the actual height of top surface and the pit defect is detected as a deeper pit than the surface depth.

Residual-type mask defect printability for extreme ultraviolet lithography

“…However, the path to establish the EUVL is not without technical difficulties, e.g., lack of sufficient light-source power, particle-free mask handling, defect-free and flat mask blanks, [1][2][3][4] and resist material development, and need to be resolved. From the viewpoint of EUV mask fabrication, mask pattern defect inspection [5][6][7] and repair [8][9][10][11][12][13] are some of the most demanding tasks to be addressed.…”

Actinic Mask Blank Inspection and Signal Analysis for Detecting Phase Defects Down to 1.5 nm in Height

“…Furthermore, the phase defect is printable even though the top surface of the multilayer could be flat. 4,5) Such defects cannot be detected by the laser-based inspection tool.…”

Observation of Residual-Type Thin Absorber Defect on Extreme Ultraviolet Lithography Mask Using an Extreme Ultraviolet Microscope

“…However, EUVL still has to meet many challenges that include the requirements of light source power, particle-free mask handling and shipping, and the development of resist material, defect-free blanks, and masks. [1][2][3][4] The required feature sizes for EUVL generation masks are considerably smaller than those encountered in optical lithography. As with newer technology nodes, the mask feature sizes are shrinking, and the specifications for pattern defect inspection 5) and defect repair [6][7][8][9] are also becoming more and more stringent.…”