A technique for the non-destructive EUV mask sidewall angle measurement using scanning electron microscope

Area of Science:

• Semiconductor manufacturing
• Metrology
• Advanced lithography

Background:

• Accurate three-dimensional (3D) mask topography verification is essential for Extreme Ultraviolet (EUV) lithography.
• EUV mask absorber sidewall angle measurement is critical for Optical Proximity Correction (OPC) and shadow effect estimation.
• Current inspection methods face challenges in precisely determining 3D mask profiles.

Purpose of the Study:

• To evaluate the efficacy of Field-Emission Critical Dimension-Scanning Electron Microscope (FE CD-SEM) for measuring EUV mask absorber sidewall angles.
• To establish a reliable method for obtaining 3D profile information from 2D SEM images.
• To validate SEM-based measurements against Transmission Electron Microscope (TEM) data.

Main Methods:

• Utilized a JEOL JSM-7401F FE CD-SEM for imaging EUV mask topography.
• Employed image processing algorithms in Matlab to accurately determine absorber edge width from 2D SEM images.
• Calculated absorber sidewall angle using measured absorber edge width and height.
• Validated SEM measurements by comparing results with TEM cross-section images.

Main Results:

• Developed a method to derive 3D profile information, specifically sidewall angle, from 2D SEM grayscale images.
• Demonstrated that absorber edge width is inversely related to sidewall angle steepness.
• Achieved an average tolerance of 0.62 degrees when comparing SEM-measured sidewall angles with TEM cross-section data.

Conclusions:

• FE CD-SEM, combined with image processing, offers a valid and accurate technique for EUV mask absorber sidewall angle measurement.
• The developed method effectively addresses the challenge of 3D profile verification in EUV mask inspection.
• SEM measurements show high agreement with TEM, indicating reliability for critical lithographic process control.