An Imaging System in Reflection Mode Using Coherent Diffraction Imaging Methods and Using Micro-Pinhole and Aperture System

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This patent describes an imaging apparatus and method that uses coherent diffraction imaging in a reflection mode to inspect flat, reflective samples—especially photomasks used in semiconductor manufacturing. The system incorporates a micro-pinhole and aperture setup to refine the light beam (such as EUV, DUV, X-ray), enhancing its coherence and enabling high-precision scanning across the sample. Reflected light from the sample is then detected and analyzed to reconstruct detailed images, including 3D tomographic data, to identify pattern defects efficiently.

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• Inspection and defect detection of photomasks used in extreme ultraviolet (EUV) and deep ultraviolet (DUV) lithography for semiconductor manufacturing.
• Quality control of optical components or precision flat reflective surfaces in high-tech industries.
• Scientific imaging of nanoscale features on reflective materials using advanced diffraction methods.
• Non-destructive testing (NDT) of multilayered reflective structures or coatings.
• Development and validation of next-generation lithography masks.

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• Higher throughput and lower cost compared to existing mask inspection technologies for the semiconductor industry.
• Improved detection sensitivity for very small defects due to enhanced coherence and imaging precision.
• Capability to provide both 2D and 3D tomographic images of the sample, enabling more comprehensive analysis.
• Non-destructive testing of expensive photomasks—critical for maintaining yield in semiconductor fabrication.
• Configurable optical setup allows adaptation to different wavelengths (EUV, DUV, X-ray), increasing versatility.
• Enhanced monochromaticity and coherence of the probing beam, leading to sharper and more accurate images.

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Patent Abstract

An apparatus and a method of imaging a reflective sample, in particular for patterned and blank DUV, EUV masks, includes making an optics system; exposing the mask to obtain an aerial image include tomographic image and developing an optical parameter of the optical system associated with the aerial image according to the micro-pinhole system using scanning coherent diffraction methods. Said apparatus comprises : a) a radiation source (10), such as an EUV source, a DUV source, a BEUV or an X-ray source, that can have a relevant low temporal or spatial coherence to emit a light beam (22); b) a first focusing element (12), such as a Fresnel plate or a toroidal mirror, in order to focus the emitted beam to the required extend; c) a mirror (16) that reflects the focused beam towards the sample (6) to be analyzed; the beam being directed at an angle of 2 to 25°, preferably at an angle of about 6°, towards the sample (6) as compared to the normal vector of the surface of the sample (6); d) a pinhole aperture plate (18) which allows with its first aperture (al) to focus and cut-off the beam diameter to the desired extent thereby forming also the beam to become more monochromatic as compared to the light beam (22) as originally emitted from the light source (10); e) a mechanism (17) to displace the sample (6) continuously or step-wise in a direction perpendicular to the normal vector of the sample surface to allow to analyze the sample (6) which reflects the light beam that has passed the first aperture (a1) of the pinhole aperture plate (18) disposed upstream of the sample (6) under the same angle of the incident light, such as 6° for example with reference to the preferred example mentioned above; f) said pinhole aperture plate (18) having a second aperture (a2) as transparent window allowing with its second aperture being disposed adjacent to the first aperture (a1) to limit the diameter of the beam reflected by the sample (6) thereby adjusting the diameter of the light beam; and g) a pixel detector (20) to analyze the reflected beam that has passed the second aperture (a2).