EUV Mask Phase Measurement Using Reflectivity and Diffraction
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Solution Overview
Problem
Current EUV lithography processes face challenges in accurately measuring the phase of reflective EUV masks, which is crucial for semiconductor miniaturization, due to insufficient resolution and defect detection sensitivity when using transmissive mask inspection equipment on reflective masks.
Innovation Solution
An apparatus and method for measuring the phase of EUV masks using an EUV light source, mirrors, a detector, and a processor to calculate the phase based on reflectivity and diffraction efficiency, specifically designed for EUV masks with distinct pattern areas for reflectivity and diffraction efficiency measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transmissive mask inspection equipment is applied to reflective EUV masks, then the existing inspection infrastructure can be utilized, but the resolution and defect detecting sensitivity are insufficient
Solution Approach 1:
The patent inverts the conventional transmissive inspection approach by using reflective EUV light interaction. Instead of light passing through the mask, the system measures how EUV light reflects off the mask surface, utilizing the mask's reflective properties to extract phase information through reflectivity and diffraction efficiency measurements.
Solution Approach 2:
The patent introduces an intermediary measurement approach by using reflectivity and diffraction efficiency as intermediate parameters. Rather than directly measuring phase, the system first measures these intermediate optical properties and then calculates phase from them, enabling indirect but accurate phase measurement.
2Reliability
If EUV light is used for reflective mask inspection, then the appropriate wavelength for EUV lithography is utilized, but it is difficult to satisfy required specifications during mask fabrication without specialized equipment
Solution Approach 1:
The patent segments the mask into distinct measurement areas: a first area for measuring reflectivity of the multilayer and absorber layer, and a second area for measuring diffraction efficiency of absorber layer patterns. This segmentation allows separate measurement of different optical properties that together determine phase, simplifying the overall measurement process.
Solution Approach 2:
The patent changes the measurement parameters from direct phase measurement to measuring reflectivity and diffraction efficiency. By changing to these more accessible optical parameters and establishing mathematical relationships between them and phase, the system achieves reliable phase measurement with standard EUV equipment.
3Productivity
If a single mask area is used for measurement, then the measurement process is simplified, but both reflectivity and diffraction efficiency cannot be measured simultaneously
Solution Approach 1:
The patent divides the mask into functionally distinct areas: a first mask pattern area with features optimized for reflectivity measurement and a second mask pattern area with features optimized for diffraction efficiency measurement. This spatial segmentation allows simultaneous measurement of both parameters without interfering with each other.
Solution Approach 2:
The patent applies local quality by designing different pattern characteristics in different mask areas. The first area has patterns suitable for reflectivity measurement while the second area has patterns suitable for diffraction efficiency measurement, allowing each area to be optimized for its specific measurement function.
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
Enables accurate phase measurement of EUV masks, improving their quality by providing correct phase information and ensuring the phase is within allowable ranges, thus enhancing the EUV lithography process.
Implementation Method 1
an EUV light source configured to generate and output EUV coherent light
Implementation Method 2
at least one mirror configured to reflect the EUV coherent light as reflected EUV coherent light into an EUV mask to be measured
Implementation Method 3
a detector configured to receive the EUV coherent light reflected from the EUV mask, to obtain a two-dimensional (2D) image, and to measure reflectivity and diffraction efficiency of the EUV mask
Implementation Method 4
a processor configured to calculate or determine a phase of the EUV mask by using the reflectivity and diffraction efficiency of the EUV mask
Data Source
AI summary
An apparatus and a method for correctly measuring a phase of an extreme ultraviolet (EUV) mask and a method of fabricating an EUV mask including the method are described. The apparatus for measuring the phase of the EUV mask includes an EUV light source configured to generate and output EUV light, at least one mirror configured to reflect the EUV light as reflected EUV light incident on an EUV mask to be measured, a mask stage on which the EUV mask is arranged, a detector configured to receive the EUV light reflected from the EUV mask, to obtain a two-dimensional (2D) image, and to measure reflectivity and diffraction efficiency of the EUV mask, and a processor configured to determine a phase of the EUV mask by using the reflectivity and diffraction efficiency of the EUV mask.