Catadioptric Objective with External Beam Delivery for Dark-Field Illumination
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Solution Overview
Problem
Existing catadioptric optical systems for semiconductor inspection face challenges in achieving high numerical aperture (NA), large field size, and low scattering for oblique dark-field imaging, particularly with UV-DUV wavelengths, due to beam delivery issues and noise from lens elements.
Innovation Solution
A catadioptric objective design incorporating a Mangin element with an extended surface and a beam delivery system using prisms or mirrors for external oblique laser dark-field illumination, allowing for high NA and large field size while minimizing stray light collection, using a combination of a three-surface Mangin element and beam delivery optics with a Fourier filter for improved sensitivity and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a collimated beam of monochromatic light is used to illuminate the wafer from inside the optical system, then oblique dark-field imaging can be achieved, but scattered and reflected light from lens elements produces noise that compromises sensitivity
Solution Approach 1:
The patent extracts the illumination source from inside the optical system and places it outside, eliminating the problem of scattered light from internal lens elements. The external illumination source illuminates the wafer through the objective lens without the light path intersecting internal optical elements that would cause scattering and reflection noise.
Solution Approach 2:
The patent introduces an external illumination system as an intermediary between the light source and the wafer. This external system includes光束 delivery optics that guide the illumination light to the wafer surface without passing through the internal lens elements of the inspection optical system, thereby preventing scattered light generation.
2Ease of operation
If a long working distance objective is used to allow external laser access to the wafer, then external illumination can be achieved, but the numerical aperture is limited to less than 0.7
Solution Approach 1:
The patent creates a universal illumination system that can provide both external beam access and high numerical aperture performance simultaneously. The system is designed to accommodate external illumination sources while maintaining the full NA capability of the objective lens by optimizing the illumination path to match the lens's acceptance angle.
Solution Approach 2:
The patent changes the illumination parameters by using external illumination with optimized beam delivery optics that can deliver light at the required angles for high NA operation. The system adjusts the illumination numerical aperture and beam angle to match the objective's full NA capability, eliminating the NA limitation imposed by long working distance constraints.
3Ease of operation
If refractive UV-DUV objectives are used for dark field applications, then external illumination can be achieved, but the field size and spectral bandwidth are limited
Solution Approach 1:
The patent employs a catadioptric optical system that combines refractive and reflective elements to overcome the limitations of purely refractive UV-DUV objectives. The composite optical design includes mirrors and lenses working together to achieve both external illumination capability and large field size with broad spectral bandwidth.
Solution Approach 2:
The patent transitions from a purely refractive optical path to a catadioptric system that utilizes reflective optics, adding a new dimensional approach to light manipulation. This allows the system to achieve large field sizes and broad bandwidth while maintaining external illumination capability, as mirrors can handle a wider range of wavelengths and angles compared to refractive elements alone.
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 design supports both bright-field and oblique laser dark-field inspection techniques with enhanced sensitivity and reduced noise, enabling the detection of defects below the optical system's resolution and maintaining high performance across a broad spectral range.
Implementation Method 1
Certain light energy reflected from the specimen passes to the second surface of the extension element, the Mangin element
Implementation Method 2
light energy reflected from the specimen passes to the second surface of the extension element, the Mangin element, and through a plurality of lenses
Implementation Method 3
An aspheric surface may be provided
Implementation Method 4
light energy may be provided to the specimen using diverting elements such as prisms or reflective surfaces
Implementation Method 5
light energy may be provided to the specimen using diverting elements such as prisms or reflective surfaces
Data Source
AI summary
A catadioptric objective configured to inspect a specimen is provided. The catadioptric objective includes a Mangin element having one surface at a first axial location and an extension element positioned together with the Mangin element. The extension element provides a second surface at a second axial location. Certain light energy reflected from the specimen passes to the second surface of the extension element, the Mangin element, and through a plurality of lenses. An aspheric surface may be provided, and light energy may be provided to the specimen using diverting elements such as prisms or reflective surfaces.