Metrology Illumination System Using PBS and Rotatable Aperture Disk
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Solution Overview
Problem
Current metrology systems in semiconductor wafer manufacturing face challenges in achieving flexible illumination spatial profiles, high polarization extinction ratios, and high contrast ratios, particularly in critical dimension (CD) and overlay (OV) metrology, due to limitations in existing illumination systems such as filter wheels and spatial light modulators.
Innovation Solution
A metrology system incorporating a polarizing beam splitter (PBS), an illumination mode selector (IMS) with apertures, and a reflective spatial light modulator (SLM) with a pixel array, which splits and modifies the illumination beam to achieve complex amplitude or intensity spatial profiles, allowing for flexible illumination and high contrast ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a polarizing beam splitter (PBS) is used to achieve high polarization extinction ratio, then measurement precision is improved, but device complexity increases due to the need for additional optical components and alignment mechanisms
Solution Approach 1:
The patent implements nested illumination modes by placing multiple aperture patterns on a single rotatable disk, where each aperture corresponds to a different illumination mode (e.g., annular, condenser, dark-field). The disk rotates to select different apertures, effectively nesting multiple functional elements into one compact component, thereby achieving high polarization extinction ratio without proportionally increasing system complexity
Solution Approach 2:
The illumination system is designed with multi-functionality by incorporating a rotatable disk that provides multiple illumination modes (annular, condenser, dark-field) and a polarizing beam splitter that can operate in different configurations. This universal design allows the same hardware to serve multiple measurement functions (CD metrology, OV metrology) while maintaining high polarization extinction ratio, reducing the need for separate dedicated systems for each function
2Adaptability or versatility
If multiple illumination modes are provided using a filter wheel with multiple aperture plates, then adaptability is improved, but device complexity and loss of time increase due to mechanical switching between plates
Solution Approach 1:
The patent consolidates multiple aperture patterns that would traditionally require separate plates on a filter wheel into a single rotatable disk with multiple apertures. Each aperture on the disk corresponds to a different illumination mode, nesting multiple functional apertures into one component. This eliminates the need for complex filter wheel mechanisms with multiple detachable plates, reducing device complexity while maintaining adaptability across different illumination modes
Solution Approach 2:
The patent merges multiple illumination mode selection functions into a single rotatable disk mechanism. Instead of using separate aperture plates that must be individually switched via a filter wheel, the design combines all aperture patterns onto one disk that rotates to select the desired mode. This merging of functions simplifies the mechanical structure, reduces the number of moving parts, and eliminates the time loss associated with switching between multiple plates
3Adaptability or versatility
If a spatial light modulator (SLM) is used to achieve flexible illumination spatial profiles, then adaptability is improved, but device complexity and cost increase due to the sophisticated modulator technology
Solution Approach 1:
The patent extracts the essential function of spatial profile control from complex spatial light modulators and implements it through simpler geometric apertures. By using carefully designed aperture shapes (annular, condenser, dark-field) on the rotatable disk, the system achieves flexible illumination spatial profiles without requiring sophisticated SLM technology. This extraction of the core function eliminates the need for expensive and complex modulator hardware while maintaining adaptability
Solution Approach 2:
The patent replaces expensive spatial light modulators with inexpensive geometric aperture patterns etched or machined onto a rotatable disk. These apertures are simple, durable, and cost-effective compared to SLM technology. The apertures can be precisely manufactured using standard fabrication techniques and do not require power, control electronics, or complex calibration, making them a cheap and reliable alternative that maintains illumination flexibility
4Measurement precision
If dark field scatterometry is used for overlay metrology to achieve high contrast ratio, then measurement precision is improved, but device complexity increases due to the need for precise blocking of zeroth order diffraction
Solution Approach 1:
The patent applies local quality by designing a dark-field aperture with a specific geometric pattern that blocks only the central zeroth-order diffraction region while allowing higher-order diffracted beams to pass. The aperture has a precise geometry (e.g., annular or multi-ring pattern) that creates localized blocking in the angular spectrum, enabling high-contrast overlay measurements without requiring complex optical path modifications. The local geometric design of the aperture achieves the dark-field effect efficiently
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 provides a flexible and high-contrast illumination solution, enhancing measurement accuracy and quality in CD and OV metrology by controlling the spatial profile of the illumination beam, thereby improving the precision of semiconductor wafer measurements.
Implementation Method 1
a polarizing beam splitter (PBS) divides light by polarization state to transmit p-polarized light while reflecting s-polarized light
Implementation Method 2
a reflective spatial light modulator (SLM) having a pixel array, the pixel array being configured to modify a spatially-resolved beam characteristic of the first sub-beam and the second sub-beam and to reflect either or both of the first sub-beam and the second sub-beam back to the IMS and PBS along a return path
Data Source
AI summary
An illumination system for a metrology apparatus that can achieve illumination spatial profile flexibility, high polarization extinction ratio, and high contrast. The illumination system includes a polarizing beam splitter (PBS), an illumination mode selector (IMS), and a reflective spatial light modulator (SLM). The PBS divides an illumination beam into sub-beams. The IMS has a plurality of apertures that transmits at least one sub-beam and may be arranged in multiple illumination positions corresponding to illumination modes. A pixel array of the reflective SLM and reflects a portion of the sub-beam transmitted by the IMS back to the IMS and PBS. The PBS, IMS, SLM collectively generates a complex amplitude or intensity spatial profile of the transmitted sub-beam.