Imaging of extreme-ultraviolet mask patterns using coherent extreme-ultraviolet scatterometry microscope based on coherent diffraction imaging

Abstract

Articles you may be interested inPhase defect characterization on an extreme-ultraviolet blank mask using microcoherent extreme-ultraviolet scatterometry microscopeIn extreme-ultraviolet (EUV) lithography, defect-free mask production is a critical issue for highvolume manufacturing. For mask inspection and metrology, we have developed a coherent EUV scatterometry microscope (CSM). It is a simple lensless system. An aerial image of the mask pattern is reconstructed with iterative calculation based on coherent diffraction imaging. Periodic patterns, aperiodic patterns, and phase structures were reconstructed well by the CSM. A defect in a line-and-space pattern was detected as a diffraction signal. The aerial image of the defect is also reconstructed. This paper demonstrates the capability of the CSM to observe complex diffraction amplitudes directly from the pattern and the defect.

Accurate characterization of mask defects by combination of phase retrieval and deterministic approach

“…The hybrid input-output (HIO) algorithm as developed by Fienup 4 is the most widely used method for reconstructing phase information from the Fourier transform modulus since it enables to avoid local minima. In the case of mask inspection for EUVL, periodic patterns can be reconstructed and defects' width can be estimated 5 . However, accuracy is not high enough to estimate the actual depth of the defect.…”

Phase defect characterization on an extreme-ultraviolet blank mask using microcoherent extreme-ultraviolet scatterometry microscope

“…[16][17][18][19][20] The sample phase defect was exposed using coherent EUV light, and the diffracted light was recorded using a CCD camera. To reconstruct the pattern image, the phase information of the diffraction image is required, but this information is not recorded.…”

“…The periodic structures of the line-and-space (L/S) and hole patterns and the aperiodic structures were reconstructed well. 17 In addition to the conventional intensity images, the phase images were also acquired by the coherent EUV scatterometry microscope (CSM). 20 The EUV-phase shift value of an absorber structure and the phase difference in the L/S pattern with shadowing effects were evaluated, because they could cause actinic critical-dimension changes.…”

Accurate characterization of mask defects by combination of phase retrieval and deterministic approach

“…Gerchberg-Saxton 13 and HIO methods have been adopted in several recent studies 1,3,5,[14][15][16][17][18][19][20] for mask inspection in EUVL. Harada et al 1,14,17 reported the development of coherent scatterometry microscope to characterize mask defect.…”

“…In the case of mask inspection for EUVL, periodic patterns can be reconstructed and defects' widths can be estimated. 5 However, it was reported that conventional phase retrieval methods, such as HIO algorithm, were not robust to noise. 6,7 In practical applications, the noise is, therefore, limiting the accuracy.…”