Simulation of image placement error due to fabrication of black border on EUV mask

Abstract

To satisfy the requirement on the image placement accuracy, it is very important to consider the stress of the films on the mask substrate. The stress of the EUV mask is much larger than several kinds of optical masks because reflective Mo/Si multilayer (ML) has large compressive stress. In recent years, thinner absorber has been proposed because of better resolution and less shadowing effect. However it results in the leakage of the light to the adjacent chips on wafer. Then the light shield around the pattern area on the mask has been developed. From the viewpoint of manufacturability, etched multilayer black border (BB) is advantageous. Pattern displacement occurs at the edge of the multilayer etched BB. Measured pattern displacement error increased near the BB and it was simulated by using finite element method. The displacement depends strongly on the ML stress and it is successfully described by the release of the compressive stress at the edge of the black border. Most of the deformation near the BB remains even if the mask is chucked to the flat surface. Simulation using various models are discussed and compared with experimental results.

High-NA EUV lithography: current status and outlook for the future

“…87) Etching the black border leads to locally reduced stress, which can displace mask features. 88) The results of careful measurements performed at Imec of pattern displacement are shown in Fig. 24.…”