Measuring and characterizing the nonflatness of EUVL reticles and electrostatic chucks
2007
According to the International Technology Roadmap for Semiconductors, meeting the strict requirements on image
placement errors in the sub-45-nm regime may be one of the most difficult challenges for the industry. For Extreme
Ultraviolet Lithography (EUVL), the nonflatness of both the mask and chuck is critical as well, due to the
nontelecentric illumination during exposure. To address this issue, SEMI Standards P37 and P40 have established the
specifications on flatness for the EUVL mask substrate and electrostatic chuck. This study investigates the procedures
for implementing the Standards when measuring and characterizing the shapes of these surfaces. Finite element
simulations are used to demonstrate the difficulties in supporting the mask substrate, while ensuring that the measured
flatness is accurate. Additional modeling is performed to illustrate the most appropriate methods of characterizing the
nonflatness of the electrostatic chuck. The results presented will aid in identifying modifications and clarifications that
are needed in the Standards to facilitate the timely development of EUV lithography.
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