OPD-Matched Interferometry for Thick TSV OCD Metrology
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Solution Overview
Problem
Existing optical critical dimension (OCD) metrology methods struggle to accurately measure thick structures with multiple reflective surfaces due to spectral smearing and loss of sensitivity, particularly in through-silicon via (TSV) manufacturing, leading to increased complexity and cost in achieving high spectral resolution.
Innovation Solution
Employing optical path difference (OPD) matched interferometry by setting the interferometer mirror to match the optical path difference with each reflective surface, allowing for coherent interference measurements by fitting and removing partially coherent terms to extract fully coherent fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high spectral resolution measurement is used to resolve spectral features for thick structures, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent divides the measurement process into multiple discrete wavelength measurements taken at different positions along the optical path. Instead of requiring a single high-resolution spectrometer, the system segments the spectral measurement into multiple lower-resolution measurements taken at different locations, which are then combined to achieve the equivalent of high spectral resolution.
Solution Approach 2:
The patent introduces an intermediary scanning mechanism that moves the measurement point along the optical path. This scanning element acts as a mediator between the light source and detector, enabling the system to achieve high spectral resolution through spatial scanning rather than requiring a complex high-resolution spectrometer.
2Measurement precision
If Fourier-based methods with scanning elements are used to achieve high spectral resolution, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent performs measurements at a limited number of discrete positions along the optical path rather than continuously scanning the entire range. By selecting specific key positions for measurement, the system achieves sufficient spectral resolution without the time penalty of a complete continuous scan.
Solution Approach 2:
The patent pre-determines the optimal measurement positions along the optical path based on the expected spectral features. This preliminary planning allows the system to focus measurements only at critical positions, reducing total measurement time while maintaining spectral resolution.
3Measurement precision
If longer wavelengths are used to reduce oscillation frequency, then spectral features become easier to resolve, but sensitivity is lost and system complexity increases
Solution Approach 1:
The patent maintains the original wavelength parameters for measurement but changes the measurement approach by taking multiple measurements at different spatial positions. This allows the system to resolve spectral features through the multi-position measurement strategy rather than by changing to longer wavelengths, thereby preserving measurement sensitivity.
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
Enhances measurement sensitivity and accuracy for thick structures by resolving fast spectral features, providing stable and detailed characterization of wafer patterns.
Implementation Method 1
The interference of reflections from surfaces at different heights causes oscillation of the measured reflection as a function of wavelength
Data Source
AI summary
A system and methods for OCD metrology are provided including setting an interferometry mirror of the system at each of multiple positions z, wherein at each position the mirror reflection is Optical-Path-Difference (OPD) matched with reflection from the at least one reflective surface, and measuring interferometer spectra Imeasured, with the mirror at each of the multiple positions; then fitting the multiple measured interferometer spectra to an equation for Imeasured, to solve for non-z-dependent parameters of the equation, leaving a z-dependent function of the wave number k, having fully coherent and partially coherent terms; and removing the partially coherent terms of the function to derive a fully coherent field for characterizing the OCD structure.