Beat Pattern Alignment for Small Metrology Targets
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Solution Overview
Problem
In lithographic processes, it is challenging to accurately align radiation spots with small targets positioned in limited spaces due to low optical contrast, which hinders precise measurement and alignment, especially when targets are smaller than 5×5 μm².
Innovation Solution
The integration of an alignment structure with a metrology structure on the target, where the alignment structure generates a high-contrast beat pattern when illuminated, aiding in the recognition and positioning of the radiation spot using computer-implemented pattern recognition, and utilizing higher order diffracted rays to enhance detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If targets are made small to fit in limited spaces, then space utilization is improved, but alignment accuracy deteriorates due to low optical contrast
Solution Approach 1:
The target is segmented into two distinct functional structures: a metrology structure for measurement and an alignment structure for positioning. The alignment structure generates a beat pattern that is separate from but complementary to the metrology structure, allowing independent optimization of each function while working together to solve the alignment accuracy problem in small targets.
Solution Approach 2:
The alignment structure is designed to generate a beat pattern with high optical contrast that appears as distinct intensity variations (peaks and troughs) in the scattered radiation signal. This optical contrast enhancement allows the alignment structure to be clearly detected even when the overall target size is reduced, directly addressing the low optical contrast issue.
2Productivity
If targets are made small for dense packaging, then productivity is improved, but detection difficulty increases due to low contrast
Solution Approach 1:
The alignment structure creates a beat pattern that produces strong intensity modulations in the scattered radiation signal. These intensity variations serve as high-contrast markers that are easily detectable by the measurement system, significantly reducing detection difficulty even when targets are densely packed and small in size.
Solution Approach 2:
The alignment structure utilizes asymmetric line width variations in periodic patterns to generate the beat pattern. This asymmetry creates distinctive intensity profiles in the scattered radiation that are easily distinguishable from background noise and other target features, enhancing detection capability in high-density target arrangements.
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 improves the alignment and measurement accuracy of small targets by increasing contrast and enabling precise positioning of radiation spots, even in areas with low optical contrast, thereby enhancing the overall metrology and lithographic process efficiency.
Implementation Method 1
the alignment structure comprises structures that are arranged to generate a beat pattern when the alignment structure is illuminated with source radiation
Implementation Method 2
certain metrology apparatuses direct a beam of radiation onto a target and measure one or more properties of the scattered radiation
Data Source
AI summary
A target formed on a substrate, the target having: an alignment structure; and a metrology structure; wherein the alignment structure comprises structures that are arranged to generate a beat pattern when the alignment structure is illuminated with source radiation. Advantageously, when the target is illuminated, the beat pattern that appears in an image of the target allows the target to be easily identified using a pattern recognition technique.