Grating Structural Parameter Correlation via Through-Focus Intensity Variation
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Solution Overview
Problem
Conventional image metrology tools face challenges in achieving high resolution due to optical diffraction, precision limitations, and cost, making them unsuitable for cost-effective and efficient measurement of critical dimensions in the semiconductor industry.
Innovation Solution
A method utilizing through focus image acquisition and focus metrics algorithms to correlate structural parameters of predetermined gratings, generating a relation formula between structural parameters and variation ratios of off-focus offsets, allowing for the determination of unknown grating parameters without requiring expensive optical or probing elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional image metrology tools are used, then cost is reduced, but measurement resolution deteriorates due to optical diffraction and precision limitations
Solution Approach 1:
The patent changes the measurement parameter from direct in-focus imaging to through-focus intensity variation analysis. By capturing images at multiple focus positions and analyzing intensity variations, the system achieves higher measurement precision without requiring more complex optical hardware, effectively resolving the contradiction between measurement resolution and device complexity
Solution Approach 2:
The patent adds the focus position dimension to the measurement process. Instead of measuring only at a single focus plane, the system captures images across multiple focus positions (through-focus sequence), transforming a 2D measurement problem into a 3D analysis (x, y, focus position), thereby achieving higher precision with conventional tools
2Measurement precision
If expensive high-resolution tools like CD-SEM and CD-AFM are used, then measurement precision is improved, but cost increases significantly
Solution Approach 1:
The patent creates a computational model (relation formula) that copies the measurement capability of expensive tools. By establishing the relationship between intensity variation and structural parameters through calibration with known gratings, the system can determine unknown parameters using conventional tools, achieving high precision measurement without the high cost of CD-SEM or CD-AFM
Solution Approach 2:
The patent replaces expensive mechanical/probing measurement systems (CD-SEM, CD-AFM) with an optical-based computational method. By substituting direct physical measurement with through-focus image analysis and mathematical modeling, the system achieves comparable precision at lower cost
3Measurement precision
If through focus image acquisition and focus metrics algorithm are used, then measurement resolution is improved, but data processing complexity increases
Solution Approach 1:
The patent performs preliminary calibration by measuring gratings with known structural parameters to establish the relation formula between intensity variation ratio and structural parameters. This pre-established model simplifies subsequent measurements, as unknown parameters can be directly calculated from the formula without complex real-time processing, balancing measurement precision with processing simplicity
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 measurement resolution, simplifies data processing, and can be applied to conventional inexpensive tools, offering rapid and accurate measurements without the need for hardware amendments.
Implementation Method 1
According to Rayleigh criteria, it is quite difficult for conventional image metrology tools to meet the prospective resolution demands due to issues such as optical diffraction
Data Source
AI summary
A method for correlating a structural parameter of a plurality of gratings acquires images from a plurality of gratings, which have different structural parameters. A focus metrics algorithm is then performed to find the off-focus offset of the orders of each grating from the intensity variation of these images, and the variation ratio of the off-focus offset to the order for each grating is calculated later. Consequently, the structural parameters of these gratings can be correlated based on the variation ratio of the off-focus offset to the order. The present method acquires images from an unknown grating at different off-focus offsets, and performs a focus metrics algorithm to find the off-focus offset of the orders of the unknown grating. The variation ratio is calculated and the structural parameter of the unknown grating is determined based on the variation ratio.