Lithographic Scatterometry Overlay Measurement via Multi-Parameter Illumination
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Solution Overview
Problem
Measurement accuracy in lithographic scatterometry is limited by grating asymmetry disturbances and sensitivity to illumination conditions, leading to inconsistent results across substrates due to process variations.
Innovation Solution
A method involving an optical measurement system that measures multiple targets with different setting values, using multiple wavelengths and equations to determine property values, allowing for improved accuracy and robustness against process variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional scatterometry measurement is used with single target and single illumination condition, then measurement process is simple, but measurement accuracy is limited due to grating asymmetry disturbances and process variations
Solution Approach 1:
The measurement process is segmented into multiple independent measurements: measuring multiple different targets (at least two) with different grating structures, and performing multiple measurements under different illumination conditions (at least two different wavelengths or polarization states). This segmentation allows each measurement to be affected differently by grating asymmetry, enabling the asymmetry to be mathematically separated from the overlay signal through regression analysis.
Solution Approach 2:
The illumination parameters are changed across multiple measurements by varying at least one of: wavelength, polarization state, or numerical aperture. This parameter variation causes the grating asymmetry disturbance to manifest differently in each measurement, while the overlay error remains constant. The system uses these parameter-dependent measurements to solve for both overlay and asymmetry parameters simultaneously through multi-parameter regression.
2Measurement precision
If multiple targets and multiple illumination conditions are used, then measurement accuracy improves, but measurement time increases
Solution Approach 1:
The system performs multiple measurements under different illumination conditions and on multiple targets in a continuous sequence without requiring physical repositioning or reconfiguration of the measurement system between measurements. The optical system maintains its position and configuration while only the illumination parameters are changed, allowing rapid acquisition of all necessary measurement data through parameter switching rather than mechanical repositioning.
Solution Approach 2:
The illumination conditions are dynamically changed during the measurement process by adjusting parameters such as wavelength, polarization state, or numerical aperture. This dynamic parameter adjustment allows the system to efficiently collect data from multiple targets under multiple conditions without static reconfiguration, reducing measurement time while maintaining the ability to separate overlay signals from asymmetry disturbances through mathematical analysis of the dynamic response.
3Ease of manufacture
If grating asymmetry is present in targets, then target fabrication is simplified, but measurement reliability deteriorates due to sensitivity to illumination conditions
Solution Approach 1:
The system uses feedback from multiple measurements taken under different illumination conditions to identify and compensate for grating asymmetry effects. By measuring the same overlay target with at least two different illumination parameters (wavelength, polarization, or numerical aperture), the system generates a set of equations that can be solved through regression analysis to separate the overlay signal from the asymmetry disturbance, thereby compensating for the asymmetry's harmful effects on measurement reliability.
Solution Approach 2:
The measurement approach combines multiple types of measurement data (different wavelengths, polarization states, or numerical apertures) into a composite analysis framework. This composite measurement strategy creates a more robust measurement system that is less sensitive to any single illumination condition or target asymmetry, as the combined information from multiple measurement modalities allows mathematical separation of overlay and asymmetry parameters.
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 measurement accuracy and reduces the impact of grating asymmetry and illumination conditions, enabling more reliable overlay and other parameter measurements across substrates.
Implementation Method 1
These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation—e.g. intensity at a single angle of reflection as a function of wavelength; intensity at one or more wavelengths as a function of reflected angle; or polarization as a function of reflected angle—to obtain a diffraction 'spectrum' from which a property of interest of the target can be determined.
Implementation Method 2
These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation
Data Source
AI summary
A method of measuring a property of a substrate, the substrate having a plurality of targets formed thereon, the method comprising:measuring N targets of the plurality of targets using an optical measurement system, where N is an integer greater than 2 and each of said N targets is measured Wt times, where Wt is an integer greater than 2 so as to obtain N*Wt measurement values; anddetermining R property values using Q equations and the N*Wt measurement values, where R<Q≤N*Wt;wherein the optical measurement system has at least one changeable setting and, for each of the N targets, measurement values are obtained using different setting values of at least one changeable setting.