Spatial Light Modulator Inspection via Checkered Phase Patterns
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Solution Overview
Problem
Spatial light modulators with arrays of microscopic mirrors face challenges in accurate inspection, particularly when microscopic mirrors fail to control height or exhibit curvature beyond tolerance, leading to deviations in the intensity distribution of spatial images on substrates, necessitating an efficient on-body inspection method without dismounting the modulator from exposure devices.
Innovation Solution
A method and apparatus for inspecting spatial light modulators by arranging optical elements in a checkered pattern between two phases, 0° and 180°, and guiding light through a projection optical system with a resolution coarser than the image width of one optical element to form a spatial image, allowing for easy characterization of the modulator's characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a spatial light modulator with an array of microscopic mirrors is used for maskless lithography, then manufacturing flexibility and cost efficiency are improved, but inspection difficulty increases due to the need to detect subtle phase errors and curvature deviations in each mirror element
Solution Approach 1:
The patent applies phase contrast imaging principles where defective mirror elements are made visible through their optical phase differences. By illuminating the SLM and detecting the interference patterns and intensity variations in the projected image, defects become detectable without physical contact or disassembly, thus resolving the inspection difficulty while maintaining manufacturing flexibility
Solution Approach 2:
The patent creates an optical copy of the SLM mirror array pattern and projects it onto a screen or sensor. This optical copying method allows non-destructive inspection of the mirror element patterns and their phase relationships, enabling defect detection without physically accessing or disassembling the SLM device
2Measurement precision
If high-resolution inspection methods are used to detect defective elements, then measurement precision is improved, but device complexity and inspection time increase
Solution Approach 1:
The patent utilizes the existing projection optical system of the lithography apparatus to perform inspection functions. The same optical components used for pattern projection are employed to image and detect defects in the SLM, eliminating the need for separate dedicated inspection equipment and reducing overall system complexity while maintaining adequate measurement precision
Solution Approach 2:
The patent changes the operational parameters of the inspection system by using the projection optical system's native resolution and magnification characteristics. Instead of requiring high-resolution microscopy, the method leverages the projection system's imaging capabilities with appropriately scaled test patterns, simplifying the inspection apparatus while achieving sufficient defect detection precision
3Measurement precision
If the resolution limit of the projection optical system is increased to resolve individual optical element images, then measurement precision is improved, but productivity decreases due to longer inspection times
Solution Approach 1:
The patent inspects only the critical regions and parameters of the SLM that affect lithography performance, rather than attempting to image every mirror element at full resolution. By focusing inspection on phase errors, curvature deviations, and pattern fidelity rather than individual element imaging, the method achieves sufficient measurement precision while maintaining high inspection speed and productivity
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
This approach enables straightforward inspection of spatial light modulators by altering the intensity distribution of the spatial image, effectively identifying deviations and ensuring accurate pattern formation on substrates, thereby preventing shape errors and maintaining high illumination light utilization efficiency.
Implementation Method 1
guiding light having passed the inspection target area to a projection optical system with a resolution limit coarser than a width of an image of one optical element, to form a spatial image
Data Source
AI summary
A method for inspecting a spatial light modulator includes: performing such control that in an inspection target area in an array of mirror elements, the mirror elements in a first state in which incident light is given a phase change amount of 0 and the mirror elements in a second state in which incident light is given a phase change amount of 180° (π) become arrayed in a checkered pattern; guiding light having passed the inspection target area to a projection optical system with a resolution limit coarser than a width of an image of one mirror element, to form a spatial image; and inspecting a characteristic of the spatial light modulator from the spatial image. This method allows us to readily perform the inspection of the characteristic of the spatial light modulator having the array of optical elements.