Grating-Over-Grating Overlay Metrology with Parallel Layer Wavelengths
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing overlay metrology systems face challenges in accurately measuring relative registration between sample layers of semiconductor devices, particularly with increasing feature sizes, necessitating more measurements and higher-order corrections, which require efficient intra-field and on-product measurements.
Innovation Solution
An overlay metrology system utilizing multi-wavelength illumination and a collection pupil aperture to selectively pass diffraction lobes from grating-over-grating structures on different sample layers, enabling accurate single-cell measurements by imaging each layer with unique wavelengths, thus eliminating rotational asymmetry errors and reducing the need for multi-cell measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of overlay measurements is increased to meet decreasing feature size demands, then measurement precision is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent segments the overlay measurement process by implementing separate imaging channels for different layers (e.g., first layer and second layer). Each channel is optimized to capture specific diffraction orders from specific layers, allowing independent measurement of each layer's contribution to overlay error. This segmentation enables precise measurement without requiring complex multi-cell structures.
Solution Approach 2:
The patent introduces wavelength as an additional dimension to differentiate between layers. By using multiple wavelengths (e.g., first wavelength for first layer, second wavelength for second layer) and collecting specific diffraction orders at each wavelength, the system can measure overlay without requiring multiple spatial cells. This dimensional approach simplifies the measurement system while maintaining high precision.
2Manufacturing precision
If correction-per-exposure measurements are implemented, then manufacturing precision is improved, but measurement time and productivity are reduced
Solution Approach 1:
The patent implements preliminary action by performing overlay measurements on product layers during the fabrication process itself, rather than requiring separate post-fabrication measurement steps. The multi-wavelength imaging system captures overlay information from different layers simultaneously or in rapid sequence, enabling real-time feedback for correction-per-exposure applications without significantly impacting fabrication throughput.
3Measurement precision
If multi-cell measurements are used to eliminate rotational asymmetry errors, then measurement precision is improved, but device complexity and target size increase
Solution Approach 1:
The patent addresses rotational asymmetry errors by using asymmetric collection of diffraction orders. Specifically, the system collects different diffraction orders (e.g., +1 and -1 orders) from overlapping gratings with different pitches, where the asymmetry in pitch values creates a measurable signal that is insensitive to rotational misalignment. This allows single-cell measurements without requiring multiple cells to average out rotational errors.
Solution Approach 2:
The patent applies local quality by designing the grating structures with different local pitches in different layers. The first grating has a first pitch and the second grating has a second pitch, creating local variations that enable layer-specific diffraction patterns. This local differentiation allows the measurement system to distinguish between layers and eliminate rotational asymmetry effects without requiring large multi-cell targets.
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 allows for efficient and accurate overlay measurements of small targets, particularly within die regions, by maximizing the numerical aperture of the objective lens and minimizing measurement errors, thereby supporting advanced semiconductor fabrication processes.
Implementation Method 1
one or more illumination sources configured to generate one or more illumination beams, each of the one or more illumination beams including two or more spectral bands having two or more center wavelengths
Implementation Method 2
components in a collection pupil to exclusively pass, for each of the two or more center wavelengths, two diffraction lobes from each of the different pitches of the grating-over-grating structures
Data Source
AI summary
An overlay metrology system may include an illumination source to generate illumination including two or more spectral bands having two or more center wavelengths. The system may include an optical sub-system to illuminate and image a sample, where the sample in accordance with the metrology recipe includes one or more cells with grating-over-grating structures formed as overlapping gratings with different pitches in different sample layers. The system may include collection pupil components to exclusively pass, for each of the two or more center wavelengths, two diffraction lobes from each of the different pitches of the grating-over-grating structures. A controller may receive images of the sample from the detectors generated in accordance with the metrology recipe and generate overlay measurements between at least some of the different layers of the sample based on the images.