Metrology Apparatus Using Dual-Angle Interference for Structure Measurement
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Solution Overview
Problem
Existing metrology apparatuses struggle to accurately determine characteristics of structures on a substrate due to unwanted contributions in interference patterns that do not originate from the structure, which affect the precision of measurements.
Innovation Solution
The method involves illuminating the structure with first and second illumination radiation from different directions, forming interference patterns with reference radiation, and adjusting the azimuthal angles of the reference radiation to reduce unwanted contributions by setting the optical path lengths equal and choosing azimuthal angles that minimize interference pattern variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single illumination direction is used to form interference patterns, then the measurement process is simple and fast, but unwanted contributions in the interference pattern reduce measurement precision
Solution Approach 1:
The measurement process is segmented into multiple illumination steps, each with a specific azimuthal angle. By dividing the measurement into discrete angular components, the system captures structure information while eliminating unwanted contributions through comparative analysis of the segmented measurements.
Solution Approach 2:
The system employs periodic illumination at different azimuthal angles to probe the structure from multiple directions. This periodic action allows the interference patterns to be modulated in a predictable manner, enabling extraction of structure characteristics while filtering out unwanted background contributions.
2Measurement precision
If multiple illumination directions are used to reduce unwanted contributions, then measurement precision improves, but the measurement time and process complexity increase
Solution Approach 1:
The system uses a limited set of specific azimuthal angles (e.g., four directions at 0°, 90°, 180°, 270°) rather than continuous angular scanning. This partial action approach provides sufficient precision improvement while minimizing the time penalty of multiple measurements.
Solution Approach 2:
The system uses feedback from the interference patterns obtained at different azimuthal angles to iteratively refine the structure characteristic determination. By comparing measurements from multiple angles and using the differences to eliminate unwanted contributions, the system achieves high precision without requiring excessive measurement time.
3Measurement precision
If azimuthal angles of reference radiation are adjusted to minimize interference pattern variations, then measurement accuracy improves, but the complexity of controlling radiation directions increases
Solution Approach 1:
The system changes the azimuthal angle parameter of the illumination and reference radiation in a systematic manner. By controlling the angular parameter across multiple measurements, the system extracts structure information while eliminating unwanted contributions through angular-dependent interference pattern analysis.
Solution Approach 2:
The system intentionally introduces asymmetry by using different azimuthal angles for illumination and reference radiation. This asymmetric configuration allows the interference patterns to encode structure information in a way that can be distinguished from unwanted symmetric background contributions.
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 of determining structural characteristics by minimizing interference pattern variations, allowing for precise measurement of features on the substrate.
Implementation Method 1
detecting on a sensor a first interference pattern formed by interference between a portion of the first scattered radiation reaching the sensor and first reference radiation
Implementation Method 2
detecting on the sensor a second interference pattern formed by interference between a portion of the second scattered radiation reaching the sensor and second reference radiation
Implementation Method 3
illuminating the structure with first illumination radiation to generate first scattered radiation
Implementation Method 4
illuminating the structure with second illumination radiation, from a different direction to the first illumination radiation in a reference frame of the structure, to generate second scattered radiation
Data Source
AI summary
Methods and apparatus are disclosed for determining a characteristic of a structure. In one arrangement, the structure is illuminated with first illumination radiation to generate first scattered radiation. A first interference pattern is formed by interference between a portion of the first scattered radiation reaching a sensor and first reference radiation. The structure is also illuminated with second illumination radiation from a different direction. A second interference pattern is formed using second reference radiation. The first and second interference patterns are used to determine the characteristic of the structure. Azimuthal angles of the first and second reference radiations onto the sensor are different.