Optical Metrology Focus Offset Correction
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Solution Overview
Problem
Optical metrology systems face imprecision and reduced throughput due to imprecision in focusing processes, especially when measuring multiple locations on a sample with unknown focus offsets, leading to inaccurate and repeatable measurement results.
Innovation Solution
The system performs optical metrology while holding the sample at an unknown focus offset, using focus calibration to determine the optical response and adjusting modeled data to fit for the focus offset as a variable parameter in model regression analysis, eliminating the need for a focusing procedure before each measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a focusing procedure is performed at each location before measurement, then measurement precision is improved, but productivity deteriorates due to time consumption
Solution Approach 1:
The patent performs a preliminary focus calibration procedure once to determine the optical response to focus offset, then uses this calibration data in model regression analysis to correct measurements taken at unknown focus offsets. This eliminates the need to perform focusing procedures at each measurement location, thereby improving throughput while maintaining measurement precision through mathematical correction.
2Measurement precision
If a focusing procedure is performed to place the sample at the focal plane, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent replaces the mechanical focusing adjustment process with a mathematical correction approach. Instead of physically adjusting the sample position to achieve focus, the system takes measurements at unknown focus offsets and uses model regression analysis with focus calibration data to mathematically correct the measurements, thereby eliminating time-consuming mechanical focusing operations.
3Measurement precision
If focusing is performed at each location on the sample, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent changes the approach from physically adjusting focus parameters to mathematically accounting for focus offset parameters. The system determines the optical response to focus offset through calibration, then uses this information in model regression analysis to correct measurements, transforming a complex mechanical focusing problem into a simpler parameter-based correction approach.
Data Source
AI summary
A metrology system performs optical metrology while holding a sample with an unknown focus offset. The measurements are corrected by fitting for the focus offset in a model regression analysis. Focus calibration is used to determine the optical response of the metrology device to the focus offset. The modeled data is adjusted based on the optical response to the focus offset and the model regression analysis fits for the focus offset as a variable parameter along with the sample characteristics that are to be measured. Once an adequate fit is determined, the values of the sample characteristics to be measured are reported. The adjusted modeled data may be stored in a library, or alternatively, modeled data may be adjusted in real-time.