Segmented Mirror Apparatus for EUV Mask Inspection
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Solution Overview
Problem
Conventional photomask inspection apparatuses using UV light are inadequate for inspecting EUV masks due to insufficient numerical apertures and large mirror sizes, leading to high production costs, complex manufacturing, and inefficient testing processes.
Innovation Solution
A segmented mirror apparatus with multiple smaller mirror segments is used, allowing for higher numerical apertures and easier handling, along with uniform coatings on each segment to mimic a graduated coating, reducing manufacturing complexity and surface distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large mirror is used to maintain telecentric condition at the image plane, then the imaging quality is improved, but the production cost and mirror weight significantly increase
Solution Approach 1:
The large mirror is divided into multiple smaller mirror segments that collectively perform the function of the original large mirror. Each segment is lighter and easier to manufacture, while the array of segments maintains the required optical performance and telecentric condition through coordinated positioning and uniform coating.
2Manufacturing precision
If a large mirror is used to maintain telecentric condition, then the imaging quality is improved, but the device complexity and mounting structure requirements increase
Solution Approach 1:
The mirror system is segmented into multiple independent units that can be mounted on simpler support structures. Each segment requires less robust mounting compared to a single large mirror, reducing the overall device complexity while maintaining imaging quality through the collective arrangement of segments.
Solution Approach 2:
Multiple mirror segments are combined to function as a unified optical element. The segments work together to maintain the telecentric condition and imaging quality, distributing the functional requirements across multiple simpler components rather than requiring one complex large mirror system.
3Manufacturing precision
If a large mirror is used, then the telecentric condition is maintained, but the manufacturing complexity and coating requirements increase
Solution Approach 1:
The manufacturing process is simplified by dividing the large mirror into smaller segments that are easier to fabricate with precise coatings. Each segment can be manufactured and coated independently using standard processes, avoiding the need for complex graduated or indexed coatings on a single large mirror surface.
4Reliability
If a large mirror is used, then the optical performance is improved, but the testing difficulty and labor requirements increase
Solution Approach 1:
The testing process is simplified by segmenting the mirror into smaller testable units. Each mirror segment can be tested independently with fewer test points required compared to a large mirror with many small sub-apertures. This reduces labor and time requirements while maintaining optical performance through verification of individual segments.
5Manufacturing precision
If a large mirror is used, then the imaging capability is improved, but the rework requirements and yield impact increase
Solution Approach 1:
The mirror system is segmented so that defects or variations in individual segments do not require rework of the entire large mirror. Each segment can be independently inspected and replaced if necessary, improving yield by allowing partial acceptance of mirror arrays rather than requiring complete rework of a single large mirror.
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 segmented mirror apparatus improves defect detection sensitivity and reduces production costs by enabling higher resolution and throughput in EUV mask inspection with reduced mirror distortion and testing complexity.
Implementation Method 1
a first mirror arranged to receive and reflect the light which is reflected from the target substrate, a second mirror which is arranged to receive and reflect the light which is reflected by the first mirror, a third mirror which is arranged to receive and reflect the light which is reflected by the second mirror, and, a segmented mirror which is arranged to receive and reflect the light which is reflected by the third mirror
Data Source
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AI summary
An apparatus for inspecting a photomask, comprising an illumination source for generating a light which illuminates a target substrate, objective optics for receiving and projecting the light which is reflected from the target substrate, the objective optics includes a first mirror arranged to receive and reflect the light which is reflected from the target substrate, a second mirror which is arranged to receive and reflect the light which is reflected by the first mirror, a third mirror which is arranged to receive and reflect the light which is reflected by the second mirror, and a segmented mirror which is arranged to receive and reflect the light which is reflected by the third mirror. The segmented mirror includes at least two mirror segments. The apparatus further includes at least one sensor for detecting the light which is projected by the objective optics.