Scatterometer Asymmetry Compensation via 180-Degree Rotation
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Solution Overview
Problem
Lithographic processes face challenges in accurately measuring overlay errors due to asymmetry in scatterometers, which can cause tool-induced shifts and errors in determining the center of the pupil plane, leading to inefficiencies and increased throughput times.
Innovation Solution
A method involving the rotation of the target pattern and scatterometer by 180° to measure two-dimensional angular scatter spectra, allowing for the calculation of sensor correction values to compensate for asymmetry, thereby reducing tool-induced shifts and improving measurement accuracy without significantly increasing throughput time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If asymmetry compensation method is applied to scatterometer, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by performing asymmetry compensation calibration before actual overlay measurements. A target pattern is measured at multiple orientations (0°, 45°, 90°, 135°) to pre-determine correction values that are stored and applied to subsequent measurements, thereby improving measurement precision without adding complexity during the actual measurement process
Solution Approach 2:
The patent implements feedback by using the measured asymmetry values from the target pattern to generate correction values that are fed back into the overlay measurement calculations. The correction values are derived from the difference between measured intensities at different orientations and are applied to compensate for instrument asymmetry in subsequent overlay measurements
2Measurement precision
If multiple orientation measurements are performed to compensate asymmetry, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent performs asymmetry compensation measurements using a target pattern at multiple orientations as a preliminary calibration step. These measurements are conducted separately from the actual overlay measurements, allowing the compensation values to be pre-determined and stored, thereby improving precision without significantly impacting the throughput time of actual production measurements
Solution Approach 2:
The patent applies self-service by using the scatterometer itself to measure a known target pattern and automatically generate correction values. The system uses its own measurement capability to characterize and compensate for its own asymmetry, eliminating the need for external calibration equipment and minimizing additional time requirements
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 effectively compensates for asymmetry, enhancing the accuracy of overlay error measurements and maintaining high processing efficiency by applying correction values to subsequent measurements, thus improving the reliability of lithographic processes.
Implementation Method 1
measuring a first two-dimensional angular scatter spectrum of radiation reflected and/or scattered by the target pattern
Implementation Method 2
measuring a first two-dimensional angular scatter spectrum of radiation reflected and/or scattered by the target pattern
Implementation Method 3
measuring a first two-dimensional angular scatter spectrum of radiation reflected and/or scattered by the target pattern by using the scatterometer to measure intensity at a plurality of pre-determined angular positions
Data Source
AI summary
In a method of measuring asymmetry in a scatterometer, a target portion is illuminated twice, first with 0° of substrate rotation and secondly with 180° of substrate rotation. One of those images is rotated and then that rotated image is subtracted from the other image. In this way, asymmetry of the scatterometer can be corrected.