Slanted Field Stop Edges for Scatterometry Metrology
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Solution Overview
Problem
Existing scatterometry metrology systems face performance degradation and accuracy errors due to edge diffraction, which interferes with grating diffraction and reduces the usability of diffraction signals, leading to measurement instabilities and repeatability issues in overlay measurements.
Innovation Solution
The system modifies field stops and target boundaries by slanting their edges with respect to the measurement direction, directing edge diffraction away from regions of interest and reducing its impact on the measurement, while maintaining the spatial periodicity of the target and grating direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If field stops and target boundaries are aligned perpendicular to measurement direction, then device complexity is minimized, but edge diffraction interferes with grating diffraction signals reducing measurement precision
Solution Approach 1:
The patent applies asymmetry by slanting the boundaries of field stops and targets at an angle (e.g., 45 degrees) relative to the measurement direction, rather than aligning them perpendicularly. This asymmetric configuration causes edge diffraction to propagate in directions that do not overlap with grating diffraction orders, thereby eliminating interference and improving measurement precision without significantly increasing device complexity
Solution Approach 2:
The patent converts the harmful edge diffraction effect into a beneficial one by strategically orienting boundaries at slanted angles. Instead of trying to eliminate edge diffraction, the invention directs it away from measurement regions, transforming what was previously a source of interference into a non-intrusive phenomenon that does not affect grating diffraction signal quality
2Measurement precision
If target boundaries are rotated to reduce edge diffraction, then measurement precision improves, but manufacturing precision becomes more difficult
Solution Approach 1:
The patent employs parameter changes by specifying standard slant angles (such as 45 degrees) for target boundaries and field stop edges. These standardized angular parameters can be directly implemented using conventional lithography and fabrication processes, maintaining manufacturing precision while achieving the desired edge diffraction reduction. The use of standard angles simplifies the manufacturing process compared to arbitrary angles
3Reliability
If field stop edges are slanted to direct edge diffraction away from measurement regions, then repeatability improves, but device complexity increases
Solution Approach 1:
The patent applies dimensionality change by introducing an angular dimension to the boundary configuration. Instead of simple perpendicular alignment (one-dimensional orientation), the field stops and targets are oriented at slanted angles, adding rotational degree of freedom. This angular dimension enables edge diffraction to be directed into previously unused spatial regions, improving repeatability while the modular nature of angular adjustment keeps device complexity manageable
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 effectively reduces edge diffraction effects, enhancing the accuracy and repeatability of scatterometry measurements by minimizing the interference of edge diffraction with grating diffraction signals and maintaining the symmetry required for precise overlay measurements.
Implementation Method 1
The target scatters the illumination radiation to form a scattered radiation
Implementation Method 2
A part of the scattered radiation undergoes diffraction by the target. The resulting scattered radiation pattern consists of several diffracted orders, according to the grating equation
Implementation Method 3
Boundaries of field stops and/or of targets may be designed to be slanted with respect to the measurement directions, to cause edge diffraction to propagate obliquely and thus reduce or remove its effects on the measured target diffraction signals
Data Source
AI summary
A scatterometry metrology system, configured to measure diffraction signals from at least one target having respective at least one measurement direction, the scatterometry metrology system having at least one field stop having edges which are slanted with respect to the at least one measurement direction.