Cross-Hatched Overlay Metrology Marks for Semiconductor Precision
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Solution Overview
Problem
Conventional overlay metrology marks in the semiconductor industry face challenges with large size, susceptibility to cross-talk, and difficulties in contrast equalization, limiting their suitability for smaller dimensions and precise measurements.
Innovation Solution
The implementation of cross-hatched overlay metrology marks, where periodic features in one layer are oriented orthogonally to those in another layer, allowing for smaller target sizes and reduced exclusion zones, enabling more efficient and accurate overlay metrology measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional side-by-side grating metrology marks are used, then overlay measurements can be obtained, but the target size becomes large (20-40 μm×20-40 μm) and exclusion zones are required to prevent cross-talk
Solution Approach 1:
The patent transitions from a two-dimensional side-by-side grating arrangement to a three-dimensional stacked configuration where gratings are positioned in different layers (first layer and second layer) with orthogonal orientations. This vertical stacking in the third dimension eliminates the need for large horizontal exclusion zones, reducing the target footprint while maintaining measurement precision through the cross-hatched pattern formed by orthogonal gratings in stacked layers.
Solution Approach 2:
The patent implements a nested structure where the second grating layer is positioned over and substantially aligned with the first grating layer, creating a compact cross-hatched pattern. The orthogonal gratings are nested within the same target area, allowing both gratings to occupy the same spatial footprint without requiring separate exclusion zones, thus reducing overall target size while preserving overlay measurement capability.
2Reliability
If exclusion zones are added to prevent cross-talk between adjacent gratings, then signal contamination is reduced, but the usable measurement area is reduced and target size increases
Solution Approach 1:
By moving from planar side-by-side gratings to vertically stacked orthogonal gratings in different layers, the patent eliminates the need for horizontal exclusion zones. The orthogonal orientation and vertical separation naturally prevent optical cross-talk between gratings, allowing the entire target area to be used for measurement without sacrificing signal quality through artificial exclusion zones.
Solution Approach 2:
The patent extracts and removes the exclusion zone concept entirely from the design. Instead of adding exclusion zones to prevent cross-talk, the orthogonal stacked grating configuration inherently prevents cross-talk through its geometric arrangement, allowing the full target area to be utilized for metrology measurements without compromising signal integrity.
3Measurement precision
If gratings are positioned side by side in adjacent layers, then overlay can be measured, but cross-talk from adjacent gratings degrades the signal
Solution Approach 1:
The patent employs asymmetric orthogonal orientations for the gratings in the first and second layers, where the grating lines in one layer are oriented at approximately 45 degrees relative to the other layer. This asymmetric angular relationship, combined with vertical stacking, creates a cross-hatched pattern that naturally prevents optical cross-talk between layers while maintaining overlay measurement precision through the distinctive cross-hatched signature.
Solution Approach 2:
By stacking gratings vertically in different layers rather than positioning them adjacently in the same plane, the patent uses the vertical dimension to eliminate optical cross-talk. The orthogonal orientation combined with vertical separation ensures that light interacting with one grating layer does not interfere with the other layer, removing cross-talk as a limiting factor while preserving measurement capability.
Data Source
AI summary
The present invention is directed to novel metrology marks and methods for their use. The marks comprise cross hashed overlay metrology marks formed on a substrate including a plurality of target regions. The mark including a first grating structure formed in one layer of a target region and including a second grating structure formed in another layer of the target region. The periodic features of the first and second grating structures are oriented substantially orthogonal one another to form a cross-hatched metrology target in the target region. Additionally, the patent discloses methods of employing the metrology marks to obtain overlay metrology measurements.