EUV Mask Backside Defect Detection via Chromatic Scanning
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Solution Overview
Problem
In EUV lithography, reflective masks 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 in integrated circuits, necessitating an efficient method for detecting and avoiding these defects during mask production.
Innovation Solution
An optical scanning system using a multi-wavelength light source and chromatic lens to focus light at different focal points, allowing 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
1Manufacturing precision
If a reflective mask is used during EUV lithography, then smaller feature sizes can be formed, but the mask becomes vulnerable to manufacturing defects such as oxidation and particles
Solution Approach 1:
The patent applies preliminary action by scanning the mask blank backside before pattern formation to detect scratches and particles. This advance detection allows defective areas to be identified and avoided before they can cause printing errors in the integrated circuit, thereby maintaining mask reliability while enabling smaller feature sizes through EUV lithography
2Reliability
If the mask blank is scanned for scratches and particles, then defect detection is achieved, but the scanning process adds complexity to the manufacturing workflow
Solution Approach 1:
The patent replaces complex mechanical scanning systems with an optical scanning approach using a light source and optical detector. This substitution simplifies the system by using well-established optical components to detect surface defects through light reflection characteristics, reducing mechanical complexity while maintaining reliable defect detection capability
3Measurement precision
If traditional scanning methods are used to detect scratches, then detection capability is provided, but the detection speed is insufficient for efficient mask production
Solution Approach 1:
The patent implements continuous scanning of the mask blank backside surface, moving the light source and detector across the entire surface to detect scratches and particles. This continuous action allows rapid coverage of large mask areas, significantly improving detection speed and mask production efficiency while maintaining high measurement precision through optical detection
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
This method allows for fast and accurate detection of scratches and particles on the mask blank's backside, preventing defects in the fabricated circuit and improving the reliability of the EUV lithography process by ensuring the quality of the mask used.
Implementation Method 1
using a multi-wavelength light source and chromatic lens to focus light at different focal points
Implementation Method 2
receiving reflected light from the surface of the substrate
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.