Overlay Measurement Device Using Wavelength-Selective Optical Filtering
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Solution Overview
Problem
Existing overlay measurement methods fail to accurately and rapidly measure overlay errors between layers with large height differences and different optical properties, as they do not account for material differences and varying magnifications.
Innovation Solution
An overlay measurement device is designed with a light source, beam splitters, color filters, a beam combiner, objective lens, and detectors to adjust wavelengths and magnifications for each overlay mark, allowing for precise imaging and error calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the same beam is used to measure both major scale and minor scale, then the measurement process is simplified, but measurement precision deteriorates because material differences and height differences are not accounted for
Solution Approach 1:
The measurement beam is segmented into multiple wavelength components, with each wavelength specifically tailored to penetrate certain materials while being reflected by others. This allows different scales formed of different materials to be measured using optimized wavelength-specific beams, resolving the contradiction between simplified process and precise measurement.
Solution Approach 2:
Different wavelengths are assigned to measure different scales based on their material properties. The measurement system adapts the beam characteristics locally to match the specific material and height characteristics of each scale being measured, thereby maintaining high precision without excessive complexity.
2Device complexity
If a single wavelength beam is used for measurement, then the device structure is simplified, but measurement precision deteriorates when layers have different optical properties
Solution Approach 1:
The wavelength parameter of the measurement beam is changed according to the optical properties of the materials being measured. By selecting appropriate wavelengths from a broadband source, the system optimizes penetration and reflection characteristics for different material layers, achieving high precision measurement across diverse optical properties.
Solution Approach 2:
A single broadband light source serves multiple functions by providing a spectrum of wavelengths that can be selectively used for measuring different material types. This multi-functional approach maintains device simplicity while achieving material-specific measurement optimization.
3Measurement precision
If different wavelengths are used for different overlay marks, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Multiple wavelength-specific measurement paths are merged into a single integrated optical system. The beam combiner combines multiple wavelength components into one beam path, allowing precise measurement of different overlay marks with material-optimized wavelengths while avoiding the complexity of separate measurement systems.
Solution Approach 2:
Optical filters serve as intermediaries that selectively transmit or reflect specific wavelengths to the appropriate measurement paths. These filter elements enable wavelength-specific measurement without requiring complex switching mechanisms or separate light sources for each overlay mark.
4Productivity
If magnification differences due to height differences are not corrected, then measurement speed is maintained, but measurement precision deteriorates
Solution Approach 1:
The measurement system dynamically adjusts the focal plane position to match the height of each overlay mark being measured. This dynamic focusing capability compensates for height-induced magnification differences without requiring mechanical repositioning of the entire measurement system, thereby maintaining measurement speed while improving precision.
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
Enables accurate and rapid measurement of overlay errors between layers with significant height and optical property differences, improving the reliability of semiconductor manufacturing by accounting for material-specific and height-related imaging challenges.
Implementation Method 1
an objective lens configured to condense the beam combined by the beam combiner at a measurement position on the wafer and collect the beam reflected from the measurement position
Implementation Method 2
a beam combiner configured to combine the beams passed through the first color filter and the second color filter
Implementation Method 3
a first beam splitter configured to split a beam emitted from the light source into two beams
Implementation Method 4
a second beam splitter configured to split the beam collected by the objective lens into two beams
Implementation Method 5
a first color filter configured to adjust a center wavelength and a band width of one of the beams split by the first beam splitter so that the center wavelength and the band width of one of the beams become suitable for acquiring an image of the first overlay mark
Implementation Method 6
a second color filter configured to adjust a center wavelength and a band width of the other of the beams split by the first beam splitter so that the center wavelength and the band width of the other of the beams become suitable for acquiring an image of the second overlay mark
Data Source
AI summary
An overlay measurement device for measuring an error between a first overlay mark and a second overlay mark respectively formed on different layers formed on a wafer is proposed. The device includes a light source, a first beam splitter configured to split a beam emitted from the light source into two beams, a first color filter configured to adjust a center wavelength and a band width of one of the beams split by the first beam splitter so that the center wavelength and the band width of one of the beams become suitable for acquiring an image of the first overlay mark.