EUV Mask Backside Scratch Detection Using Multi-Wavelength Scanning
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Solution Overview
Problem
Reflective masks used in extreme ultraviolet (EUV) lithography are vulnerable to manufacturing defects such as oxidation and particles, and scratches on the backside of the mask can cause defects on the front side, leading to printing errors during integrated circuit fabrication, necessitating an efficient method for detecting and avoiding these defects.
Innovation Solution
An optical scanning system utilizing a multi-wavelength light source and chromatic lens to focus light at different focal points, allowing for the detection of bumps and dips on the mask blank's backside by identifying the wavelength with peak intensity, which corresponds to the height or depth of surface features, enabling precise mapping and avoidance of defective areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional scanning methods are used to detect defects on mask blank backside, then detection thoroughness is improved, but scanning time increases
Solution Approach 1:
The patent segments the scanning process into two distinct stages: a fast pre-scan phase that covers the entire mask blank surface to identify potential defect regions, and a detailed inspection phase that focuses only on identified defect areas. This segmentation allows the system to maintain high detection thoroughness while significantly reducing overall scanning time by avoiding detailed inspection of all areas.
Solution Approach 2:
The patent applies partial action by performing detailed inspection only on regions where defects are suspected, rather than conducting exhaustive detailed inspection across the entire mask blank surface. The fast pre-scan identifies candidate regions, and subsequent detailed inspection is applied partially only to those regions, optimizing the balance between detection precision and time consumption.
2Measurement precision
If multi-wavelength light source is used for surface height detection, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent introduces a chromatic lens as an intermediary component that focuses different wavelengths of light at different distances. This intermediary element enables the system to measure surface height by detecting the focal position of reflected light for each wavelength, providing precise height information without requiring complex multi-component optical systems for each wavelength.
Solution Approach 2:
The patent utilizes parameter changes by varying the wavelength of incident light and measuring the corresponding focal distance. By changing the wavelength parameter and observing how the focal position shifts, the system can determine surface height with high precision. This approach converts a complex spatial measurement problem into a wavelength-dependent optical parameter measurement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method allows for fast and accurate detection of scratches and particles on the mask blank's backside, preventing defects in the fabricated integrated circuits by ensuring the mask is free from bumps and dips, thereby improving the reliability of the EUV lithography process.
Implementation Method 1
a chromatic lens is used to focus light at different focal points
Implementation Method 2
light is scattered by the surface features and the scattered light is detected
Data Source
AI summary
A method of scanning a substrate and determining scratches of the substrate includes transmitting a converging beam of light that comprises multiple wavelengths to the substrate. Each wavelength of the multiple wavelengths focuses at a different distance in a focus interval around and including a surface of the substrate. The method also includes receiving reflected light from the surface of the substrate and determining a height or depth of the surface of the substrate based on a wavelength of the reflected light having a highest intensity.