Differential Polarimetric Interferometry for Etch Depth Measurement
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Solution Overview
Problem
Current methods for measuring etching depth during glow discharge spectrometry are inaccurate and unreliable, especially for low etching depths, due to variations in etching speed and composition, and rely on calibration with reference samples assuming homogeneous density.
Innovation Solution
A differential polarimetric interferometry method that separates light beams to form interferometric signals, normalizes these signals to account for variations in reflection coefficients, and calculates optical phase shifts to determine etching depth in real-time, using orthogonal polarization components for enhanced accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration-based etching depth measurement is used, then measurement can be performed, but accuracy deteriorates due to variations in etching speed and composition
Solution Approach 1:
The patent changes the measurement parameter from time-based (calibration method) to optical path difference-based (interferometry). By measuring the optical phase shift of reflected light rather than relying on etching rate calibration, the system achieves accurate depth measurement that is independent of etching speed variations and material composition changes.
Solution Approach 2:
The patent replaces the mechanical/calibration-based measurement system with an optical interferometry system. Instead of using physical reference samples and time-based calculations, the system uses light wave interference patterns to directly measure etching depth, eliminating the need for calibration assumptions about homogeneous density and constant etching rates.
2Measurement precision
If reference sample calibration is used, then etching depth can be estimated, but measurement precision deteriorates for low etching depths
Solution Approach 1:
The patent changes the measurement approach from indirect time-based estimation to direct optical path difference measurement. The interferometric method measures the actual physical depth by counting interference fringes, providing precise measurement even for sub-micron etching depths where calibration methods fail due to their reliance on assumed constant etching rates.
3Measurement precision
If polarimetric interferometry is used, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent introduces a polarizing beam splitter and quarter-wave plates as intermediary optical components to separate and recombine light beams with controlled polarization states. These intermediaries enable the measurement of optical path difference through polarization modulation, achieving high precision depth measurement while maintaining a manageable optical system configuration.
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 method provides more precise and less noisy measurements of etching depth, overcoming variations in the etching process and allowing for real-time estimation without the need for calibration assumptions, thus improving the accuracy and reliability of etching depth analysis.
Implementation Method 1
recombination of the first reflected beam and of the second reflected beam to form an interferometric beam
Implementation Method 2
the first incident beam being directed towards a first zone of a sample exposed to an etching treatment to form a first reflected beam
Implementation Method 3
separation in polarization of the interferometric beam into at least a first polarization component and a second polarization component orthogonal to each other
Data Source
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AI summary
The invention relates to a method for measuring etch depth comprising the following steps: - separating a light beam (2) into a first, and respectively second, incident beam (21, 22) directed towards a first, respectively second, area (11, 12) of a sample (10) exposed to an etching treatment to form a first, and respectively second, reflected beam (31, 32), - recombining the first reflected beam and the second reflected beam to form an interferometric beam; detecting a first, and respectively second, interferometric intensity signal relative to a first, respectively second, polarisation component (35, 37); calculating a lower envelope function and an upper envelope function of a differential polarimetric interferometry signal; determinating an offset function and a normalisation function from the first lower envelope function and the first upper envelope function; and calculating a differential polarimetric interferometry function normalised locally at each instant (t).