Tunable Light Source Interferometer for Axial Resolution
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Solution Overview
Problem
Current imaging interferometers face challenges in accurately determining the distance between a reference surface and raised surface features on a sample, particularly in semiconductor devices, due to limitations in wavelength selection and coherence length control, which affect axial resolution and measurement precision.
Innovation Solution
The implementation of a tunable light source system that emits multiple light beams with different wavelengths, combined with a processor system that generates interference patterns and performs frequency domain transforms, allows for precise determination of distances by constructing fringe patterns and selecting appropriate wavelengths based on the sample's topography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed wavelength light source is used in the interferometer, then the system structure is simple, but the axial resolution and measurement precision are limited
Solution Approach 1:
The patent applies the dynamics principle by implementing a tunable light source that can dynamically adjust its wavelength rather than using a fixed wavelength source. This allows the interferometer to optimize axial resolution by selecting appropriate wavelengths based on the specific measurement requirements and sample characteristics, thereby improving measurement precision without requiring a completely complex system redesign
Solution Approach 2:
The patent implements parameter changes by varying the wavelength of the light source to optimize measurement precision. By changing the wavelength parameter, the system can achieve different axial resolutions suitable for different measurement scenarios, effectively improving measurement capability while maintaining reasonable system complexity
2Measurement precision
If multiple wavelengths are used to improve measurement precision, then the axial resolution increases, but the device complexity and processing requirements increase
Solution Approach 1:
The patent applies preliminary action by performing frequency domain transforms and fringe pattern analysis through a processor system that is pre-configured to handle multiple wavelength data. This preprocessing and analysis capability is built into the system architecture, allowing the complex processing requirements of multi-wavelength measurements to be managed systematically rather than ad hoc
Solution Approach 2:
The patent introduces an intermediary processor system that mediates between the multi-wavelength light source and the final measurement results. This processor performs frequency domain transforms and fringe pattern construction, effectively managing the complexity of multiple wavelength measurements and converting them into accurate distance determinations
3Measurement precision
If the coherence length is not controlled, then the light source is simpler, but the measurement precision of surface features is reduced
Solution Approach 1:
The patent implements parameter changes by controlling the coherence length of the light source to match the specific measurement requirements. By adjusting the coherence length parameter, the system can optimize surface feature measurement precision while maintaining a relatively simple light source design, avoiding the need for complex coherence control mechanisms
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 enhances the axial resolution and measurement precision of surface features, enabling accurate determination of distances and topography across semiconductor devices with improved efficiency and accuracy.
Implementation Method 1
The reflected beam may be a coherent addition of a first reflection of the beam off the surface of the reference plate, a second reflection of the beam off the raised surface feature and a third reflection off the floor of the sample or substrate
Implementation Method 2
a first reflection of the beam off the surface of the reference plate, a second reflection of the beam off the raised surface feature and a third reflection off the floor of the sample
Data Source
AI summary
A method of improving axial resolution of interferometric measurements of a 3D feature of a sample may comprise illuminating the feature using a first limited number of successively different wavelengths of light at a time; generating an image of at least the 3D feature based on intensities of light reflected from the feature at each of the successively different wavelengths of light; measuring a fringe pattern of intensity values for each corresponding pixel of the generated images; resampling the measured fringe patterns as k-space interferograms; estimating interference fringe patterns for a spectral range that is longer than available from the generated images using the k-space interferograms; appending the estimated interference fringe patterns to the respective measured fringe patterns; and measuring the height or depth of the 3D feature using the measured interference fringe patterns and appended estimated fringe patterns.