Diffractive Facet Mirrors for EUV Lithography Beam Shaping

The patent changes the fundamental parameter of beam shaping from geometric surface form to diffractive phase modulation. Instead of manufacturing complex spherical or aspherical surface forms, the invention uses planar or simple curved surfaces with diffractive grating structures that achieve beam shaping through phase diffraction. This parameter change from geometric to diffractive optics resolves the contradiction by enabling precise beam control with simpler manufacturing.

The invention replaces the mechanical/optical system of precise surface form manufacturing with a diffractive optical system. Instead of relying on mechanically manufactured surface precision, the patent uses diffractive gratings with sub-wavelength structures that achieve beam shaping through interference and diffraction effects. This substitution eliminates the need for complex surface form manufacturing while maintaining or improving beam control precision.

The patent shifts the critical manufacturing parameter from macroscopic surface form (which is difficult to control with conventional methods) to microscopic grating period and depth (which can be controlled with lithographic techniques). The diffractive approach allows manufacturing with standard semiconductor fabrication processes, achieving both ease of manufacture and high precision imaging quality simultaneously.

The invention moves the precision requirement from the surface geometry dimension to the sub-wavelength grating structure dimension. By creating periodic structures with periods smaller than the wavelength of EUV radiation, the patent achieves precise beam control through diffraction effects while using manufacturing processes designed for sub-wavelength feature creation, thus improving imaging quality without sacrificing manufacturability.

The patent changes the mechanism of beam shaping from geometric surface form to diffractive phase modulation. Simple planar surfaces are combined with diffractive grating structures that impose phase variations on the incident beam. This parameter change allows the use of simple surfaces while achieving sophisticated beam shaping and homogenization through the diffractive phase profile encoded in the grating structure.

The invention creates a composite optical element combining a simple substrate surface with a diffractive grating structure and multilayer coating. The composite structure integrates the manufacturing simplicity of planar surfaces with the beam shaping capability of diffractive optics, achieving both ease of manufacture and superior beam control through the synergistic combination of these elements.