Permanent Window Spectral Reference for Metrology Drift
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Solution Overview
Problem
Conventional metrology systems require frequent replacement of production wafers with reference samples to correct for light source non-uniformity and drift, significantly reducing productivity due to the need for periodic measurement and re-loading of reference samples.
Innovation Solution
A spectrographic workpiece metrology system uses a calibrated optical viewing window as a permanent secondary reference to generate a correction factor, allowing successive production workpieces to be measured without re-loading a reference sample, with periodic checks on the viewing window's reflectance spectrum to account for system drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference samples are periodically loaded to correct for light source non-uniformity and drift, then measurement accuracy is improved, but productivity deteriorates due to frequent wafer replacement
Solution Approach 1:
The patent introduces an optical viewing window as an intermediary reference element that remains permanently positioned in the measurement system. This window serves as a mediator between the light source and production wafers, providing continuous reference measurements without requiring physical replacement of production samples. The window's stable optical properties enable ongoing correction of light source variations while maintaining uninterrupted wafer measurement flow.
Solution Approach 2:
The patent creates a permanent optical copy/reference (the viewing window) that replicates the function of periodic reference samples. Instead of repeatedly loading physical reference samples, the system uses the window's reflected light as a stable reference signal that can be measured continuously. This optical copy provides the necessary reference information without requiring material replacement, thus eliminating productivity losses associated with frequent sample changes.
2Reliability
If reference samples are frequently replaced to generate correction functions, then system drift compensation is improved, but measurement time is increased due to re-loading operations
Solution Approach 1:
The viewing window is pre-positioned and permanently installed in the optical path before production measurements begin. This preliminary setup eliminates the need for repeated reference sample loading operations during the measurement process. The window remains in place throughout production, providing continuous reference measurements that compensate for system drift without interrupting the measurement flow or requiring time-consuming re-loading operations.
Solution Approach 2:
The patent enables continuous measurement operations by maintaining the viewing window in a fixed, permanent position throughout the production process. The reference measurements are obtained continuously through the window without interruption, allowing the system to maintain drift compensation while measuring production wafers back-to-back without time losses associated with periodic reference sample replacement.
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 eliminates the need for frequent reference sample loading, increasing productivity by allowing continuous measurement of production wafers while maintaining accurate correction for light source non-uniformity and drift.
Implementation Method 1
obtain a reflectance spectrum of the window; measuring through the window a reflectance spectrum of a reference sample
Implementation Method 2
The reflected light is collected and dispersed by a wavelength separation element, such as a diffraction grating
Data Source
AI summary
In a spectrographic workpiece metrology system having an optical viewing window, the viewing window is calibrated against a reference sample of a known absolute reflectance spectrum to produce a normalized reflectance spectrum of the reference sample, which is combined with the absolute reflectance spectrum to produce a correction factor. Successive production workpieces are measured through the window and calibrated against the viewing window reflectance, and transformed to absolute reflectance spectra using the same correction factor without having to re-load the reference sample.