EUV Mask Backside Scratch Detection Using Multi-Wavelength Focus
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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 determining the wavelength with peak intensity, which corresponds to the height or depth of surface features, enabling precise mapping and identification of areas requiring repair.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional scanning methods are used to detect defects on mask blank backside, then detection coverage is achieved, but detection speed is slow and time-consuming
Solution Approach 1:
The patent changes the optical parameters by using multiple wavelengths of light simultaneously, where each wavelength focuses at a different depth. This allows parallel detection of surface and subsurface features, dramatically increasing detection speed without sacrificing coverage
Solution Approach 2:
The system uses periodic modulation of the light source and synchronized detection to efficiently scan through different focal depths, enabling rapid acquisition of depth-resolved defect information across the entire mask blank backside
2Measurement precision
If multi-wavelength light focusing is used to detect surface and subsurface defects, then detection precision is improved, but system complexity increases
Solution Approach 1:
The patent employs a chromatic lens that serves multiple functions simultaneously: it focuses different wavelengths at different depths, acts as a spectral separator, and provides depth resolution. This single optical element performs what would otherwise require multiple separate optical systems, reducing overall complexity
Solution Approach 2:
The chromatic lens acts as an intermediary that translates wavelength information into spatial focus information. By using this optical mediator, the system efficiently maps the complex multi-wavelength focal plane problem into a manageable single-plane detection problem at the sensor
3Reliability
If comprehensive backside scanning is performed to detect all potential defects, then detection coverage is maximized, but processing time increases
Solution Approach 1:
The system performs preliminary classification of defects by depth using wavelength-based focusing before detailed analysis. Surface defects, subsurface defects, and bulk defects are pre-sorted by their focal wavelength, allowing efficient targeted processing and reducing the time needed for comprehensive analysis
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 defects on the mask blank's backside, preventing printing errors and ensuring the quality of the integrated circuit fabrication process by effectively identifying and addressing scratches and particles, thereby improving the reliability of the EUV lithography process.
Implementation Method 1
an optical system, e.g., a chromatic lens, focuses the beam of light on a surface of the substrate, e.g., a backside surface of the substrate
Implementation Method 2
a beam of light reflected from the surface of the substrate is received
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 a highest intensity.