Overlay Metrology Optics for Multi-Wavelength Mark Height Detection
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Solution Overview
Problem
Existing overlay measurement devices face challenges in accurately measuring overlay errors between layers with large height differences and different optical properties, as they rely on a single light source that struggles to distinguish between marks formed of different materials and under varying layers.
Innovation Solution
An overlay measurement device employing multiple light sources of different wavelengths, with a hot mirror for long wavelengths and a cold mirror for short wavelengths, along with apertures and cylinder lenses, to accurately measure the heights of overlay marks on different layers by optimizing signal detection based on wavelength-specific properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single light source is used for auto focus measurement, then the device complexity is reduced, but the measurement precision deteriorates when measuring marks with different optical properties and height differences
Solution Approach 1:
The patent divides the single light source into multiple light sources with different wavelengths (first light source with first wavelength, second light source with second wavelength). Each light source is dedicated to measuring specific overlay marks based on their optical properties, thereby resolving the contradiction between device simplicity and measurement precision for heterogeneous marks.
Solution Approach 2:
The patent applies different wavelengths of light to different overlay marks based on their specific optical properties. The first light source with first wavelength is used for marks with certain optical characteristics, while the second light source with second wavelength is used for marks with different optical characteristics, achieving locally optimized measurement precision.
2Illumination intensity
If a short wavelength light source is used, then the detector signal for the second overlay mark is enhanced, but the detector signal for the first overlay mark becomes too weak for accurate measurement
Solution Approach 1:
The patent changes the wavelength parameter of the light source to match the optical properties of different overlay marks. By selecting appropriate wavelengths (first wavelength for first overlay mark, second wavelength for second overlay mark), the patent optimizes the detector signal intensity for each mark type, resolving the contradiction between signal enhancement and measurement accuracy.
3Illumination intensity
If a long wavelength light source is used, then the detector signal for the first overlay mark is enhanced, but the detector signal for the second overlay mark becomes too weak for accurate measurement
Solution Approach 1:
The patent employs parameter changes by selecting different wavelengths for different measurement targets. The first light source uses a wavelength optimized for the first overlay mark, while the second light source uses a wavelength optimized for the second overlay mark, thereby maintaining high detector signal intensity and measurement precision for both mark types simultaneously.
4Ease of operation
If overlay marks on different layers with large height differences are measured using a single wavelength, then the measurement process is simplified, but the ability to distinguish between marks of different materials and layers deteriorates
Solution Approach 1:
The patent segments the measurement process by assigning different wavelengths to different overlay marks based on their layer positions and material properties. This segmentation enables clear distinction between marks on different layers while maintaining an automated measurement process, resolving the contradiction between operational simplicity and measurement capability.
Solution Approach 2:
The patent introduces wavelength as an intermediary parameter to distinguish between overlay marks on different layers. By using wavelength-specific interaction with different materials and layer structures, the system achieves enhanced mark distinction capability while keeping the measurement process automated and relatively simple.
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 precise measurement of overlay errors between layers with significant height differences and varying optical properties, improving the accuracy and reliability of semiconductor manufacturing processes.
Implementation Method 1
a hot mirror disposed between the first light source and the objective lens and configured to reflect light having a long wavelength in the first beam emitted from the first light source toward the objective lens
Implementation Method 2
a cold mirror disposed between the second light source and the objective lens and configured to reflect light having a short wavelength in the second beam emitted from the second light source toward the objective lens
Implementation Method 3
an objective lens configured to condense the first beam and the second beam at the measurement position of the wafer and collect the beam reflected at the measurement position
Data Source
AI summary
An overlay measurement device measures an error between a first overlay mark and a second overlay mark respectively formed on different layers formed on a wafer. The device is configured to detect a height of the first overlay mark based on a change in the signal of the first detector according to a change in the relative position of the objective lens with respect to the wafer in the optical axis direction and detect a height of the second overlay mark based on a change in the signal of the second detector according to a change in the relative position of the objective lens with respect to the wafer in the optical axis direction.