Sub-Segmented Metrology Mark Structure for Overlay Accuracy
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Solution Overview
Problem
Existing lithographic processes face challenges in accurately determining the position of metrology marks on substrates due to variations in the stack of layers, which affect angular reflectance and wavelength of reflected beams, and are sensitive to linear apodization effects of non-zeroth diffraction orders.
Innovation Solution
The use of sub-segmented grating structures for metrology marks, where segments are configured with varying pitch, duty cycle, and line width to minimize or maximize specific characteristic functions, reducing sensitivity to layer stack variations and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional metrology marks are used with standard grating structures, then the measurement process is simple, but the measurement precision deteriorates due to sensitivity to layer stack variations and linear apodization effects
Solution Approach 1:
The grating structure is divided into multiple segments along the grating vector, where each segment has different optical properties (such as different fill factors or materials). This segmentation allows the metrology mark to differentiate between overlay errors and process variations, thereby improving measurement precision while managing structural complexity through systematic division
Solution Approach 2:
Different segments of the grating structure are assigned different local properties (such as varying fill factors, materials, or geometries) to optimize their response to specific types of errors. This local differentiation enables the metrology mark to be less sensitive to linear apodization effects and layer stack variations, improving positioning accuracy without requiring uniform complexity throughout the entire structure
2Measurement precision
If the grating structure is optimized to minimize characteristic functions, then measurement accuracy improves, but the manufacturing complexity increases
Solution Approach 1:
The grating structure parameters (such as fill factor, pitch, line width, or material composition) are specifically adjusted and optimized to minimize the characteristic functions that cause sensitivity to overlay errors. By carefully selecting these parameters, the metrology mark achieves improved measurement accuracy while maintaining manufacturability through controlled parameter variations rather than complex structural changes
3Reliability
If sub-segmented grating structures are implemented, then sensitivity to layer stack variations is reduced, but the device complexity increases
Solution Approach 1:
The grating is segmented into multiple sections along the grating vector, with each segment having distinct optical characteristics. This segmentation enables the metrology mark to distinguish between overlay misalignment and process-induced variations, thereby improving measurement reliability while managing design complexity through systematic structural division
Solution Approach 2:
The grating structure is designed to dynamically respond to different types of errors through its segmented architecture. By analyzing the differential response of each segment to overlay errors versus process variations, the system achieves improved robustness while keeping the design manageable through controlled dynamic behavior rather than static complexity
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
Enhances the accuracy of metrology mark positioning by minimizing characteristic function changes due to layer stack variations, thereby improving overlay control and process robustness in lithography processes.
Implementation Method 1
sensitive to linear apodization effects of non-zeroth diffraction orders
Implementation Method 2
affect angular reflectance and wavelength of reflected beams
Data Source
AI summary
A structure of a semiconductor device with a sub-segmented grating structure as a metrology mark and a method for configuring the metrology mark. The method for configuring a metrology mark may be used in a lithography process. The method may include determining an initial characteristic function of an initial metrology mark disposed within a layer stack. The method also includes perturbing one or more variables of the plurality of subsegments of the metrology mark (e.g., pitch, duty cycle, and/or line width of the plurality of subsegments) and further perturbing a thickness of one or more layers within the layer stack. The method further includes iteratively performing the perturbations until a minimized characteristic function of an initial metrology mark is determined to set a configuration for the plurality of subsegments.