Angularly Resolved Scatterometer Calibration Method
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Solution Overview
Problem
Current calibration methods for angularly resolved scatterometers cannot separately determine the properties of ingoing and outgoing optical systems, which are essential for accurate measurements of generic targets with diffraction orders, and require additional hardware for separate measurements of these systems.
Innovation Solution
A method involving two distinct arrangements to measure radiation in different combinations of ingoing and outgoing directions, allowing for the separation of ingoing and outgoing optical system properties through modeling and comparison of these measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a known thin film reference target is used for calibration, then the product of ingoing transmission and outgoing transmission can be determined for one combination of rays, but separate determination of Tin and Tout for different combinations of ingoing and outgoing coordinates cannot be achieved
Solution Approach 1:
The calibration problem is segmented by separating the determination of ingoing transmission (Tin) and outgoing transmission (Tout) into independent components. The patent uses multiple measurements with different diffraction orders to isolate and determine Tin and Tout separately, rather than only determining their product together. This segmentation enables accurate calibration for scatterometry of generic targets with diffraction orders.
Solution Approach 2:
The patent introduces an additional dimension by utilizing multiple diffraction orders (different spatial frequencies) to create a system of equations that can be solved for separate Tin and Tout. By measuring at different diffraction angles and orders, the calibration process gains enough independent equations to separate the two transmission components that cannot be separated with a single zeroth-order measurement.
2Measurement precision
If separate measurements of ingoing and outgoing optical systems are performed, then accurate calibration for generic targets can be achieved, but additional hardware is required
Solution Approach 1:
The existing scatterometer hardware is made multi-functional by using it to measure multiple diffraction orders from a single target. The same optical system that measures zeroth order targets is also used to measure first and higher diffraction orders, eliminating the need for separate measurement hardware while enabling separate determination of Tin and Tout through the additional measurement data.
Solution Approach 2:
The calibration process uses the scatterometer's own capabilities to calibrate itself. By measuring multiple diffraction orders with the existing hardware, the system generates enough information to separately determine Tin and Tout without requiring external calibration equipment or additional measurement systems. The scatterometer performs its own calibration using its inherent ability to measure scattered radiation at different angles.
Data Source
AI summary
Calibration of an angularly resolved scatterometer is performed by measuring a target in two or more different arrangements. The different arrangements cause radiation being measured in an outgoing direction to be different combinations of radiation illuminating the target from ingoing directions. A reference mirror measurement may also be performed. The measurements and modeling of the difference between the first and second arrangements is used to estimate separately properties of the ingoing and outgoing optical systems. The modeling may account for symmetry of the respective periodic target. The modeling typically accounts for polarizing effects of the ingoing optical elements, the outgoing optical elements and the respective periodic target. The polarizing effects may be described in the modeling by Jones calculus or Mueller calculus. The modeling may include a parameterization in terms of basis functions such as Zernike polynomials.