The holographic stepper is significantly less expensive than the projection one due to a much simpler optical scheme. No need for complex and extremely costly projection optics because the sub-wavelength holographic mask (SWHM) acts not only as a photomask but also as imaging optics.
Most of the light wave aberrations that might be caused by optical system elements in SWHL, may be taken into account during the mask computer synthesis — thus we have much softer quality requirements to the optical system.
Also such optical scheme allows scaling of aerial image either by shifting SWHM along the optical axis, or by slightly changing the wavelength of the light source.
