Lithography

Which technique illuminates the mask from oblique directions to improve the resolution of fine patterns?

  1. AOPC (optical proximity correction)
  2. BOff-axis illumination
  3. CPhase-shift mask
Show answer and explanation

Answer: B. Off-axis illumination

For fine periodic patterns, diffracted light spreads so widely that it no longer enters the lens. Illuminating at an angle allows both the zeroth- and first-order diffracted light to enter the lens, resolving finer patterns. There are annular, dipole and quadrupole illuminations, optimized for each pattern.

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