Multi-Wavelength Phase Mapping for Surface Topography and Material Properties
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Solution Overview
Problem
Current optical metrology methods, such as scanning white light interferometry and ellipsometry, face challenges in distinguishing between true height variations and phase changes caused by material variations, leading to errors and requiring prior knowledge of surface composition for correction, and they struggle to produce spatial maps of optical or dielectric properties and topographic properties effectively.
Innovation Solution
The method involves generating phase maps of a target surface using radiation at multiple wavelengths to determine characteristics like optical or dielectric properties and topography by calculating phase shifts and relative Phase Shift on Reflection (PSoR), allowing for direct measurement of surface changes and material properties through spatial phase mapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If common optical metrology methods (SWLI, PSI, digital holography) are used for non-contact surface topography measurement, then surface topography can be measured, but the methods cannot distinguish between true height variations and phase changes caused by material variations, leading to measurement errors
Solution Approach 1:
The patent applies parameter changes by utilizing multiple wavelengths of light to illuminate the sample. By measuring phase maps at different wavelengths and analyzing the wavelength-dependent phase shift variations, the method can distinguish between topographic phase changes (which are wavelength-independent) and material-induced phase changes (which are wavelength-dependent). This resolves the contradiction by enabling accurate separation of height variations from material variations through spectral parameter variation.
2Measurement precision
If ellipsometry is used to measure Phase Shift on Reflection (PSoR), then average PSoR values can be obtained, but the measurement spot size is relatively large (>10 μm) and cannot easily produce spatial maps
Solution Approach 1:
The patent applies segmentation by dividing the measurement process into multiple spatial locations across the sample surface. By systematically moving the illumination and detection system to different positions and acquiring phase maps at each location, the method builds up a spatial map of PSoR values. This segmentation approach enables both accurate local PSoR measurement and comprehensive spatial mapping, resolving the contradiction between measurement precision and spatial coverage.
3Measurement precision
If prior knowledge of surface composition is used to apply correction factors, then some measurement errors can be corrected, but the process becomes more complex and requires additional information that may not be available
Solution Approach 1:
The patent applies self-service by enabling the measurement system to automatically determine material properties without requiring prior knowledge or external correction factors. By measuring phase maps at multiple wavelengths and analyzing the spectral characteristics of phase shift variations, the method self-calibrates and directly extracts both topographic and material information from the measurements themselves. This eliminates the need for external correction procedures and reduces measurement complexity.
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 accurate determination of surface characteristics by separating true height variations from material-induced phase changes, providing distinct or combined maps of topography and material properties with improved precision and simplicity compared to existing techniques.
Implementation Method 1
providing a phase map for a first region of a target surface via radiation having a first wavelength; providing n further phase maps for the first region via radiation having a further n wavelengths each different from the first wavelength
Implementation Method 2
Reflected light undergoes a phase-shift that varies with the material composition of the reflecting surface. For brevity this phase change will be labelled the Phase Shift on Reflection (PSoR)
Data Source
AI summary
Embodiments of the present invention provide a method of determining at least one characteristic of a target surface, comprising providing a phase map for a first region of a target surface via radiation having a first wavelength, providing n further phase maps for the first region via radiation having a further n wavelengths each different from the first wavelength, and determining at least one characteristic at the target surface responsive to the first and further phase maps.