Fabrication of Blazed Diffractive Optics by Through-Mask Oxidation

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This invention describes a new method for fabricating blazed diffractive optical elements, such as shallow-angle blazed gratings, on semiconductor (especially silicon) substrates. The process uses a spin-coated resist, gray-scale lithography or nanoimprint lithography to create thickness-controlled diffusion masks, followed by thermal oxidation and selective etching. This enables the production of low-roughness, precisely shaped blazed profiles suitable for advanced optical applications.

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• Manufacturing high-efficiency blazed diffraction gratings for use in X-ray or EUV (extreme ultraviolet) monochromators and spectrometers.
• Producing advanced optical elements (like zone plates, holograms, condensers, or beam shapers) for synchrotron sources and X-ray free-electron lasers.
• Creating optics for chirped pulse amplification schemes in ultrafast laser systems.
• Fabricating masters for mass replication of blazed optical elements using nanoimprint lithography.
• Developing custom diffractive optics for beam shaping, wavefront correction, or complex optical manipulation tasks.
• Producing diffractive optics that operate efficiently from hard X-rays to the infrared spectrum.

BenefitsContent extracted from patent full text and abstract with AI.

• Enables fabrication of extremely smooth (sub-nanometer roughness) surfaces, crucial for high-performance optical applications.
• Allows precise control of blaze angle and profile, improving diffraction efficiency and customization.
• Supports creation of both straight and curved line profiles; not limited to traditional straight gratings.
• Suitable for both flat and curved substrates, increasing design flexibility.
• Streamlines the production process—multiple grating types or structures can be fabricated in a single lithography and oxidation run.
• Reduces costs and complexity compared to traditional ruled or ion-beam etched blazed gratings, making high-end optics more accessible.
• Does not require crystallographic alignment of the silicon substrate, simplifying manufacturing.

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Patent Abstract

The present invention discloses a method to manufacture a low-angle blazed grating on a semiconductor substrate, such as a silicon substrate, said method comprising the steps of: a) the semiconductor substrate is spin-coated with a layer of resist, such as for example hydrogen or poly-silsesquioxane,with a thickness typically between 100 nm and 1000 nm, preferably a few hundreds of nanometers; b) a gray-scale irradiation lithography exposure step is applied to resist spin-coated on silicon substrate to generate a dose modulated pattern into the resist layer wherein the dose is varying locally in response to the density of the absorbed energy from the irradiation lithography exposure step; c) developing the coated and irradiated substrate in a suitable solution, such as for example TMAH or NaOH, thereby enabling a blazed profile comprising structures of thickness-dependent diffusion barriers, such as silicon dioxide SiO2, with a height in the range from 0 nm to 1000nm to emerge; d) performing a thermal oxidation step in an oxygen atmosphere at elevated temperature with the developed substrate thereby converting the upper layer of the silicon substrate into silicon dioxide to the depth depending on the thickness of the pattern in the resist layer above; and e) removing silicon dioxide in a hydrofluoric acid fluid thereby creating a low-angle low-roughness blazed grating structure on silicon substrate.