Kirkpatrick-Baez EUV Optical System for High-Resolution Metrology
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Solution Overview
Problem
Current optical metrology technologies face challenges in achieving high resolution for characterizing patterns with shrinking critical dimensions, particularly when using soft X-ray or Extreme Ultraviolet radiation, as they often lack the necessary resolution and efficiency for precise focusing and spectral analysis.
Innovation Solution
An optical system comprising a Kirkpatrick-Baez reflector combination with aberration-correcting reflectors and a diffractive element is designed to focus radiation in the soft X-ray or EUV spectral range, providing a two-stage focusing mechanism with a spectrometer for spectral intensity determination, optimizing demagnification, and accommodating compact volume constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical metrology technologies are used to characterize patterns with shrinking critical dimensions, then the measurement capability is limited, but the resolution is insufficient
Solution Approach 1:
The patent transitions from conventional optical wavelengths to soft X-ray or EUV radiation wavelengths, representing a fundamental change in the physical parameter (wavelength) of the measurement beam. This parameter change enables resolution of patterns with critical dimensions below the diffraction limit of conventional optics, directly resolving the contradiction between measurement capability and resolution.
Solution Approach 2:
The patent replaces conventional refractive optical systems with a reflective optical system using Kirkpatrick-Baez mirrors. This substitution is necessary because conventional lenses cannot focus soft X-ray or EUV radiation effectively, and the reflective system achieves the required focal spot size and depth of focus for high-resolution metrology of sub-10nm patterns.
2Manufacturing precision
If soft X-ray or EUV radiation is used to achieve higher resolution, then the wavelength is reduced, but the focusing capability deteriorates due to beam divergence
Solution Approach 1:
The patent employs Kirkpatrick-Baez mirrors with specific curved surfaces (cylindrical and toroidal geometries) to focus the highly divergent soft X-ray or EUV beam. The curved reflective surfaces are designed to converge the divergent radiation from the synchrotron source to a tight focal spot, achieving the required focal dimensions (e.g., 10-100 nm) despite the inherent beam divergence of soft X-ray radiation.
Solution Approach 2:
The optical system incorporates adjustable mirror positions and angles to dynamically optimize the focal spot characteristics. The mirrors can be positioned and oriented to achieve the desired focus on the substrate, and the system can adapt to different measurement conditions and pattern geometries, making the focusing capability flexible and controllable.
3Manufacturing precision
If a two-stage focusing system is implemented to achieve high resolution, then the focal spot quality is improved, but the system complexity increases
Solution Approach 1:
The patent divides the focusing function into two separate stages: a first Kirkpatrick-Baez mirror for initial focusing in one direction, and a second Kirkpatrick-Baez mirror for focusing in the orthogonal direction. This segmentation of the focusing function into independent stages allows each mirror to be optimized for its specific task, achieving a tight circular focal spot while maintaining manageable system complexity through functional decomposition.
Solution Approach 2:
The patent combines the focusing functions of two orthogonal mirror pairs into a unified optical system that delivers a single, well-defined focal spot on the substrate. The first and second Kirkpatrick-Baez mirrors work together as an integrated system, with their combined effect producing the high-quality focal spot required for metrology, while sharing common support structures and control systems to mitigate complexity.
4Measurement precision
If the optical system is designed for high resolution, then the measurement accuracy is improved, but the volume constraints are violated
Solution Approach 1:
The patent utilizes the grazing incidence geometry of the Kirkpatrick-Baez mirrors, where the optical path is arranged at shallow angles relative to the substrate plane. This dimensional arrangement allows the long optical path required for high-resolution focusing to be accommodated in a compact footprint by extending the path in the lateral dimension rather than requiring large vertical or horizontal space, thus satisfying volume constraints while maintaining measurement accuracy.
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 system achieves high-resolution imaging and spectral analysis, enabling precise characterization of patterns with improved focal spot quality and efficiency, even with large beam divergence, thereby overcoming the resolution limitations of existing metrology technologies.
Implementation Method 1
The second stage may comprise a Kirkpatrick-Baez reflector combination
Implementation Method 2
An optical system for focusing a beam of radiation on a region of interest
Implementation Method 3
The diffractive element may be configured to spatially separate spectral components of the beam of radiation
Implementation Method 4
The spectrometer may be configured to determine spectral intensities of the beam of radiation
Data Source
AI summary
An optical system (OS) for focusing a beam of radiation (B) on a region of interest in a metrology apparatus is described. The beam of radiation (B) comprises radiation in a soft X-ray or Extreme Ultraviolet spectral range. The optical system (OS) comprises a first stage (S1) for focusing the beam of radiation at an intermediate focus region. The optical system (OS) comprises a second stage (S2) for focusing the beam of radiation from the intermediate focus region onto the region of interest. The first and second stages each comprise a Kirkpatrick-Baez reflector combination. At least one reflector comprises an aberration-correcting reflector.