Variable-Width Overlay Target for Non-Flat Layer Errors
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Solution Overview
Problem
Existing lithography processes face challenges in accurately calculating overlay errors due to non-flat previous layers, leading to inaccuracies in alignment.
Innovation Solution
An overlay target with multiple working zones and line segments of varying widths, where the distance from the center determines the segment width, allowing for accurate measurement of overlay errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional overlay marks with uniform line segments are used, then the device structure is simple, but measurement precision deteriorates due to non-flat surfaces causing inaccurate overlay error calculation
Solution Approach 1:
The patent applies local quality by varying the width of line segments based on their position relative to the center of the overlay target. Line segments farther from the center have greater widths, while those closer to the center have smaller widths. This non-uniform width distribution creates different sensitivity responses across the target, enabling accurate overlay error measurement even when the previous layer surface is non-flat, thus resolving the contradiction between measurement precision and structural simplicity.
2Measurement precision
If line segments of varying widths are used in the overlay target, then measurement precision improves for non-flat surfaces, but device complexity increases
Solution Approach 1:
The overlay target is segmented into multiple working zones, each containing multiple line segments with specifically designed varying widths. This segmentation allows the system to handle complex measurement requirements by dividing the target into functional regions, where each segment contributes differently to the overall measurement accuracy, thereby managing device complexity through structured organization.
Solution Approach 2:
The patent changes the geometric parameter of line segment width based on their radial distance from the center. This parameter change creates a gradient structure where width varies continuously or discretely across the target, enabling the system to compensate for surface non-flatness effects and achieve accurate overlay error measurement without requiring complex additional components.
3Reliability
If uniform line segments are used, then ease of manufacture is high, but reliability of overlay measurement deteriorates on non-flat surfaces
Solution Approach 1:
By implementing local quality through position-dependent line segment widths, the patent enhances measurement reliability across varying surface conditions. The varying widths create differential responses that allow the measurement system to distinguish between true overlay errors and artifacts caused by surface non-flatness, thereby improving reliability while maintaining a relatively simple manufacturing process.
Data Source
AI summary
An overlay target that includes a plurality of working zones and a plurality of line segments. The line segments in each of the working zones have a plurality of widths and are parallel to each other.