Stokes Ellipsometry Using SHG for Fast Wafer Polarization Analysis
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Solution Overview
Problem
Conventional ellipsometric methods in semiconductor manufacturing face limitations due to mechanical rotation uncertainties, noise from background light, and slow data acquisition times, which degrade precision and accuracy in characterizing semiconductor wafers.
Innovation Solution
Nonlinear Optical Stokes Ellipsometry (NOSE) utilizes Second Harmonic Generation (SHG) with a femtosecond pulsed laser and an electrically tunable optical retarder to rapidly generate and analyze polarized light without mechanical components, enabling precise and fast characterization of semiconductor wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mechanical rotation of polarizing optics is used to generate incident polarization states, then complete polarization analysis can be achieved, but measurement precision deteriorates due to mechanical rotation uncertainties
Solution Approach 1:
The patent replaces mechanical rotation of polarizing optics with electro-optic modulation using a photoelastic modulator (PEM). The PEM uses acoustic vibrations to induce birefringence that modulates polarization states electronically, eliminating mechanical rotation uncertainties and improving measurement precision while maintaining the ability to generate complete polarization states.
Solution Approach 2:
The patent changes the control parameter from mechanical rotation angle to electro-optic modulation frequency and amplitude. By controlling the PEM with specific acoustic frequencies and voltages, different polarization states are generated through parameter modulation rather than mechanical movement, achieving both precision and versatility.
2Loss of information
If broadband incoherent light is used for spectroscopic ellipsometry, then spectral information is obtained, but noise from background light increases
Solution Approach 1:
The patent uses continuous wave (CW) laser light instead of broadband incoherent light, maintaining continuous illumination while eliminating the spectral complexity that causes background noise. The CW laser provides stable, monochromatic light that reduces background interference while still enabling complete polarization analysis through the PEM modulation.
Solution Approach 2:
The patent extracts only the necessary spectral information by using a tunable CW laser that can be adjusted to specific wavelengths of interest, rather than using broadband light that contains all wavelengths. This selective wavelength approach removes unnecessary spectral components that contribute to background noise while retaining the ability to obtain spectral information when needed.
3Productivity
If continuous wave laser light is used for single wavelength ellipsometry, then measurement speed improves, but measurement precision deteriorates due to lack of spectral information
Solution Approach 1:
The patent combines CW laser speed with PEM electro-optic modulation to achieve fast polarization analysis. The PEM rapidly modulates the polarization states at high frequencies (e.g., 50 kHz), enabling quick acquisition of complete polarization data without mechanical rotation, thus maintaining both speed and precision.
Solution Approach 2:
The patent uses periodic modulation of the polarization states through the PEM at high frequencies. This periodic action allows rapid cycling through multiple polarization states, enabling fast data acquisition while the periodic nature provides well-defined measurement points that maintain precision through consistent, repeatable modulation cycles.
4Adaptability or versatility
If mechanical rotation of polarizing optics is used, then polarization analysis is performed, but data acquisition time increases due to slow mechanical movement
Solution Approach 1:
The patent replaces slow mechanical rotation with fast electro-optic modulation using the PEM. The PEM can modulate polarization states at frequencies up to hundreds of kHz, reducing data acquisition time from seconds to milliseconds while maintaining the full capability to analyze all polarization states through electronic control.
Solution Approach 2:
The patent employs high-frequency periodic modulation of polarization states through the PEM, cycling rapidly through the required polarization configurations. This periodic action at high frequencies enables complete polarization analysis to be completed in a fraction of the time required by mechanical rotation, significantly reducing data acquisition time.
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
NOSE provides high precision, accuracy, and speed in determining optical properties of semiconductor wafers, allowing for fast and accurate characterization of integrated circuits and defects with improved spectral specificity and reduced noise.
Implementation Method 1
Nonlinear Optical Stokes Ellipsometry (NOSE) utilizes Second Harmonic Generation (SHG) with a femtosecond pulsed laser
Implementation Method 2
an electrically tunable optical retarder to rapidly generate and analyze polarized light
Data Source
AI summary
Described herein are methods and systems for measuring polarization states of nonlinearly generated light by a sample illuminated in response to receiving an incident beam having a known polarization state to determine a characteristic of the sample. The system includes an optical ellipsometer configured to be included in-line of a semiconductor fabrication line and generate measured signals proportional to different polarization parameters of second-harmonic light nonlinearly generated light by the sample, allowing determination of a complete polarization state of the second harmonic light using a characteristic of the sample is determined.