Rapid inspection of a projection optics incorporated to 193 nm excimer-exposure system is important for 90 nm node and beyond IC manufacturing. The measurement accuracy of the projection optics, which comprises of dozens of refractive mirrors and has numerical aperture (NA) of 0.75, should be reach 2.0 nm RMS. The high brightness subnanometer accuracy spherical wave with NA of 0.75 is crucial to realize such high accuracy metrology. In this paper, we introduce a new illumination source for Shack-Hartmann wavefront sensor used to measure the wavefront error of the projection optics. The new illumination source, which contains many randomly distributed pinholes etched on a metal membrane, acts as many incoherent point sources and has high brightness. The diameters of the pinholes are in the same order as the wavelength of the illumination wave. The diffraction of the pinholes is calculated based on finite difference time domain (FDTD) method, the diffractive waves can cover the whole space behind the pinholes, the wavefront error of the diffracted spherical wave is about 10-3λ RMS (λ=193 nm) within NA 0.75. The brightness is improved to N (Number of pinholes) times compared with single pinhole case.
High quality spherical wave, which is typically generated by the pinhole diffraction, is the core for calibration of the high-accuracy wavefront testing. The quality of the spherical wave diffracted by the pinhole is mainly determined by pinhole’s thickness, diameter, shape, material and illumination parameters. In this paper, we analyze the effect of illumination parameters such as the aberrations and numerical aperture (NA) on the quality of the spherical wave diffracted by the pinhole based on finite difference time domain (FDTD) method. The results show that the wavefront error of the spherical wave is about 8.4E-4 λ RMS when the NA of the illumination light is 0.75 and the diameter of the pinhole is 200 nm. Wavefront error of the diffracted spherical wave increases as the NA of the aberrant illumination beam increasing. Compare with astigmatism, defocus and spherical aberration, coma has the largest effect on the wavefront quality and is the most difficult aberration to filter. The conclusion supports important reference for determining the illumination parameters in calibration of high accuracy wavefront testing system.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.