Semiconductor Thickness Mapping Using Wavelength Decoupling
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Solution Overview
Problem
Current methods for measuring thickness variations in ultra-thin silicon layers of semiconductor-on-insulator structures, such as FDSOI, face limitations in spatial resolution and accuracy, particularly at small wavelengths, leading to significant measurement errors and increased manufacturing cycle times.
Innovation Solution
A method utilizing a quasi-monochromatic light flux with a selected wavelength corresponding to the minimum sensitivity of reflectivity for the buried oxide layer, combined with a calibration and correction curve, to accurately map thickness variations in the silicon layer, allowing for precise measurements across multiple zones with reduced error.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ellipsometry or spectral reflectometry with multiple optical wavelengths is used to measure thickness of both silicon and buried oxide layers, then measurement coverage of multiple layers is achieved, but measurement time increases significantly and spatial resolution is limited to wavelengths greater than or equal to about 40 μm
Solution Approach 1:
The patent extracts the measurement of the silicon layer thickness from the combined multi-wavelength measurement process. By selecting a specific wavelength where the buried oxide layer's reflectivity sensitivity is at a minimum, the measurement is decoupled into two independent steps: first measuring the buried oxide layer thickness independently, then measuring the silicon layer thickness using the selected wavelength without interference from the oxide layer variations.
Solution Approach 2:
The patent changes the wavelength parameter from a multi-wavelength approach to a single-specific-wavelength approach. The wavelength is specifically chosen to correspond to a minimum of the sensitivity of the reflectivity with respect to the buried oxide layer, thereby transforming the measurement condition to eliminate cross-interference and reduce measurement complexity.
2Productivity
If single optical wavelength measurement is used to reduce measurement time, then measurement speed improves, but thickness determination accuracy is insufficient because the measured thickness depends on both the silicon layer thickness and the underlying buried oxide layer characteristics
Solution Approach 1:
The patent introduces an intermediary measurement step for the buried oxide layer thickness. This intermediary measurement is performed first using ellipsometry or spectral reflectometry, and then this obtained thickness value is used as a known parameter in the single-wavelength measurement of the silicon layer, thereby eliminating the coupling effect and enabling accurate thickness determination.
3Manufacturing precision
If measurements are conducted at spatial wavelengths as small as 0.5 μm to achieve fine resolution, then thickness variation mapping precision improves, but conventional ellipsometry cannot achieve this resolution
Solution Approach 1:
The patent replaces the conventional ellipsometry measurement system with a simplified single-wavelength reflectivity measurement system. This substitution enables measurements at much smaller spatial wavelengths (down to 0.5 μm) by using the specific wavelength selection criterion that eliminates the need for complex multi-wavelength analysis, thereby achieving fine resolution thickness variation mapping.
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 enhances measurement accuracy to within 1% error, compatible with industrial implementation, by using a single wavelength for all structures with the same product specifications, thereby improving the efficiency and precision of thickness mapping in semiconductor structures.
Implementation Method 1
acquiring, with an image acquisition system, an image of at least one zone of the surface of the structure, the image being obtained by reflecting a quasi-monochromatic light flux on the zone of the surface of the structure
Implementation Method 2
processing the acquired image so as to determine, from intensity variations of the light reflected by the surface, a map of the thickness variations of the first layer
Data Source
AI summary
A method for measuring thickness variations in a first layer of a semiconductor structure includes: acquiring an image of at least one zone of the surface of the structure, processing the acquired image so as to determine a map of the thickness variations of the first layer, and comparing the intensity of each pixel of the image with a predetermined calibration curve, the calibration curve being determined for a given thickness of a second layer of the structure, and measuring the thickness of the second layer in the at least one zone, -if the measured thickness is different from the thickness of the second layer considered in the calibration curve, using a correction curve to determine a corrected map of thickness variations of the first layer.