Lithography Metrology Calibration Using Sub-Target Segmentation
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Solution Overview
Problem
Current calibration techniques for metrology apparatuses in lithographic manufacturing are limited in reducing measurement mismatches, often resulting in variations of around 5 nm 2σ, due to inability to account for all sources of non-ideality.
Innovation Solution
A method involving the arrangement of sub-targets in multiple positions within an illumination spot, measuring diffracted intensities, and solving a system of equations to determine scaling factors, offset parameters, and corrected intensities, thereby reducing measurement errors without bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current calibration techniques are used for metrology apparatuses, then the calibration process is simple and fast, but measurement mismatch varies around 5 nm 2σ due to inability to account for all sources of non-ideality
Solution Approach 1:
The target is divided into multiple sub-targets arranged in different positions within the illumination spot. Each sub-target experiences different non-idealities (spot inhomogeneity, sensor asymmetry, stray light) depending on its position. By measuring multiple sub-targets and solving a system of equations, the method segments the error sources and corrects for them individually, reducing measurement mismatch from 5 nm 2σ to potentially 0.25 nm 3σ.
Solution Approach 2:
The calibration method moves from a single measurement point to multiple positions within the illumination spot (spatial dimension). By arranging sub-targets in different disjunct portions of the illumination spot and measuring diffracted intensities at each position, the method adds spatial dimensionality to the calibration process, enabling detection and correction of position-dependent errors.
2Measurement precision
If multiple sub-targets are measured in different positions within the illumination spot, then measurement error modeling becomes more accurate, but the measurement and calculation process becomes more complex
Solution Approach 1:
The method uses measured diffracted intensities from multiple sub-targets as feedback to solve a system of equations and determine scaling factors, offset parameters, and corrected intensities. This feedback loop enables accurate modeling of measurement errors by using actual measurement data to calculate correction parameters, improving measurement precision despite increased complexity.
Solution Approach 2:
The method changes multiple parameters simultaneously: scaling factors for different positions, offset parameters for each disjunct portion, and corrected intensities for each sub-target. By varying and solving for multiple parameters in a systematic way, the method achieves accurate error modeling while providing a structured approach to managing the increased complexity.
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 enables more accurate modeling of measurement errors and reduces measurement mismatch across a population of metrology apparatuses to potentially as low as 0.25nm 3σ.
Implementation Method 1
measuring, for each configuration, an intensity of electromagnetic radiation diffracted from each respective sub-target
Data Source
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Figure 5~5(d)
AI summary
A method is provided for measuring a characteristic feature or property of a sub-target (e.g., a component of an integrated circuit, IC, fabricated using a lithography production process). The sub-target is located on a target, which includes one or more other sub-targets. The method involves arranging each of the sub-targets in a plurality of disjunct positions within an illumination spot of electromagnetic radiation and measuring the intensity of electromagnetic radiation diffracted from each of the sub-targets at those respective positions. Corrected intensities of electromagnetic radiation diffracted by the corresponding sub-target are determined.