Lithography

In immersion lithography with very high numerical aperture (NA), why does light polarization need to be considered?

  1. ABecause polarization changes the wavelength of light
  2. BBecause polarization changes resist thickness
  3. CBecause light arrives at large angles, the strength of interference (image contrast) depends on the polarization direction
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Answer: C. Because light arrives at large angles, the strength of interference (image contrast) depends on the polarization direction

At high NA, light hits the wafer at large angles. Whether the electric fields of interfering beams line up then depends on the polarization direction, causing differences in image contrast. Illumination with polarization controlled to suit the pattern is therefore used.

  • A. Polarization does not change wavelength.
  • B. Polarization does not change resist thickness.
  • C. Correct. At large angles, polarization changes image contrast.
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More Lithography questions

  1. What is the main cause of "flare", a problem in EUV lithography?
  2. In EUV masks, what is the phenomenon called in which the absorber pattern's thickness is not negligible compared with the wavelength, so obliquely incident light casts shadows and otherwise affects the image?
  3. What are the weak spots in a layout called, which lithography or process simulation predicts are prone to patterns bridging or breaking?
  4. Why has gas released from resist (outgassing) been a concern in EUV lithography?
  5. Based on the resolution formula R = k1 × λ / NA, how can resolution be improved (R made smaller)?