Trench Depth Measurement Using 45-Degree Diffraction Grating
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Solution Overview
Problem
Existing methods for measuring the depth of trench patterns on substrates face challenges in accuracy due to polarization effects and thin film influences, particularly when using diffraction gratings and spectral interference techniques, which limit the precise determination of trench depths, especially with thin films or multilayer films.
Innovation Solution
The method involves applying illumination light to a substrate with a trench pattern, spectrally dispersing the reflected light using a diffraction grating oriented between 40 to 50 degrees, and comparing the measured spectral reflectance with calculated spectra using parameters like trench depth and area ratios to determine the trench depth accurately, while considering the influence of film thickness and polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diffraction grating is used to spectrally disperse reflected light for measuring trench depth, then spectral reflectance can be obtained, but measurement accuracy deteriorates due to polarization effects causing large differences in diffraction efficiency between p-polarized and s-polarized light
Solution Approach 1:
The patent changes the orientation angle parameter of the diffraction grating to 45 degrees relative to the trench pattern direction. This specific parameter change optimizes the measurement by balancing the diffraction efficiency for both p-polarized and s-polarized light components, thereby reducing polarization-induced measurement errors and improving trench depth measurement accuracy
2Measurement precision
If film thickness is included as a parameter in spectral reflectance comparison for trench depth measurement, then measurement completeness is improved, but measurement accuracy deteriorates when the film is extremely thin (e.g., 10 nm) because parameter values cannot be determined with accuracy
Solution Approach 1:
The patent extracts the film thickness parameter from the simultaneous parameter set used in spectral reflectance comparison. By measuring and fixing the film thickness independently before trench depth measurement, the complex multi-parameter optimization problem is decomposed into simpler sequential measurements, enabling accurate determination of trench depth without the interference of thin film parameter coupling
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 allows for accurate measurement of trench depth by minimizing the impact of polarization and film thickness variations, enabling precise determination of trench patterns even with thin films or multilayer structures.
Implementation Method 1
spectrally dispersing reflected light of the illumination light from the substrate by a diffraction grating
Implementation Method 2
a cycle of peak in the spectrum caused by an optical path difference between the uppermost face of the substrate and the bottom face of the trench
Data Source
AI summary
In a trench shape measuring apparatus, a substrate having a trench pattern extending in a predetermined trench direction on a measurement area is held by a holding part. A light emission part applies illumination light to the measurement area and reflected light of the illumination light from the measurement area is spectrally dispersed by a diffraction grating of a spectroscope, to acquire a measured spectral reflectance. Since the diffraction grating is arranged so that an angle formed between a direction on the substrate corresponding to a grating direction of the diffraction grating and the trench direction becomes 45 degrees, even if an oscillation direction of the reflected light from the substrate is limited by influence of the trench pattern, it is possible to accurately obtain a spectral reflectance of the measurement area without influence of polarization of the reflected light and obtain a depth of the trench pattern with accuracy.