1 April 2005 Impact of mask errors and lens aberrations on the image formation by a vortex mask
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J. of Micro/Nanolithography, MEMS, and MOEMS, 4(2), 023006 (2005). doi:10.1117/1.1897392
Abstract
The images projected by the first vortex via masks, which comprised arrays of closely spaced dark spots that could pattern contacts with critical dimensions smaller than a third of an exposure wavelength in negative photoresist, showed several unexpected anomalies. Under certain conditions, the contact holes were elliptical (rather than round), displaced from their ideal locations, and had major axes oriented in directions that broke the expected symmetries. These effects have now been explained in terms of errors in the mask transmission and phase that give rise to unwanted Fourier components of the image combined with aberrations in the projection lens. Both effects must be present to break all the pattern symmetries. Distortions can be controlled by setting the numerical aperture of the projection lens to filter out four of the nine Fourier components and by proper design of the reticle.
Yasuyuki Unno, Takeaki Ebihara, Marc David Levenson, "Impact of mask errors and lens aberrations on the image formation by a vortex mask," Journal of Micro/Nanolithography, MEMS, and MOEMS 4(2), 023006 (1 April 2005). http://dx.doi.org/10.1117/1.1897392
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KEYWORDS
Photomasks

Diffraction

Imaging systems

Image acquisition

Electromagnetism

Spiral phase plates

Error analysis

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