Diffraction Overlay Alignment Patterns With Multi-Offset Sampling
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Solution Overview
Problem
The existing diffraction-based overlay metrology technique for semiconductor memory devices is prone to noise, which affects the accuracy of pattern precision and robustness across layers, necessitating more effective sampling of asymmetry data to improve measurements.
Innovation Solution
Incorporating a pair of alignment patterns with multiple offsets in a single image capturing setup, allowing for increased overlay samples and improved accuracy in estimating overlay with reduced process steps and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional DBO metrology technique is used with single offset sampling, then measurement process is simple, but measurement accuracy is reduced due to noise
Solution Approach 1:
The alignment pattern is segmented into multiple segments with different offset values (e.g., -D1, -D2, 0, +D2, +D1) along the overlay direction. Each segment provides an independent asymmetry measurement point, allowing multiple samples to be obtained from a single pattern structure. This segmentation enables noise reduction through statistical averaging while maintaining a relatively simple overall structure.
Solution Approach 2:
The invention extends the measurement approach from a single offset point to multiple offset points along the overlay direction (one dimension). By incorporating segments at different offset positions, the system captures asymmetry data across a dimension, enabling more robust overlay estimation without requiring multiple separate measurements or complex multi-dimensional sampling.
2Measurement precision
If multiple sampling steps are implemented to reduce noise, then measurement accuracy improves, but process time and cost increase
Solution Approach 1:
Multiple asymmetry measurements that would traditionally require separate sampling steps are merged into a single measurement process. The alignment pattern includes multiple segments with different offsets, all of which can be measured simultaneously in one image capture or scan. This combining of multiple measurement functions into a single operation reduces process time while maintaining the noise reduction benefits of multiple samples.
Solution Approach 2:
The alignment pattern is pre-configured with multiple segments at different offset positions before the measurement process begins. This preliminary structuring allows the measurement system to obtain multiple asymmetry data points from a single pass, eliminating the need for multiple sequential sampling steps. The preparatory design of the pattern enables efficient data collection that reduces measurement time.
3Measurement precision
If more offset samples are captured, then overlay estimation accuracy improves, but data processing complexity increases
Solution Approach 1:
The measurement system uses feedback from asymmetry measurements at multiple offset segments to iteratively refine the overlay estimation. By comparing the measured asymmetries at different offset positions with the known segment positions, the system can calculate and refine overlay values. This feedback mechanism enables accurate overlay determination while maintaining manageable data processing requirements through systematic analysis of the asymmetry-offset relationships.
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 accuracy and robustness of overlay measurements by capturing multiple offset data points in a single image, reducing noise and increasing measurement efficiency without the need for additional sampling steps.
Implementation Method 1
a diffraction-based overlay (DBO) metrology technique has been used. In the DBO metrology technique, a light may be irradiated from above a semiconductor device including a plurality of layers having similar patterns in an alignment pattern region. Asymmetry of intensities of diffraction of light from the plurality of layers is obtained.
Data Source
AI summary
Apparatuses and methods of overlay measurement are disclosed. An example apparatus includes first and second layers. The first layer includes a first alignment pattern that includes a first line extending in a first direction. The first line includes first, second and third segments. The second layer above the first layer includes a second alignment pattern including: a second line extending in the first direction above the first segment and having a first offset from the first segment in a second direction perpendicular to the first direction; a third line extending in the first direction above the second segment and having a second offset from the second segment in the second direction; and a fourth line extending in the first direction above the third segment and having a third offset from the third segment in the second direction. The first, second and third offsets are different from one another.