Optical Sensor Film Thickness Measurement Top Layer Model
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Solution Overview
Problem
Current film thickness measurement techniques in semiconductor manufacturing rely on multi-layer models that require detailed information about underlying structures, which can be incomplete or unknown, leading to inaccurate measurements and the need for time-consuming model optimization.
Innovation Solution
A method and apparatus using a top-layer model that measures film thickness based on broadband illumination reflectivity spectra, employing Fourier Transform analysis to isolate the primary peak unaffected by underlying structures, allowing for nanometer-level sensitivity without requiring information about the underlying layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multi-layer models are used for film thickness measurement, then measurement coverage can be expanded to include underlying structures, but measurement accuracy deteriorates due to incomplete or unknown information about underlying structures
Solution Approach 1:
The patent extracts and isolates the top layer optical response from the overall multi-layer system by using Fourier Transform to separate frequency components. The primary peak in the FT spectrum corresponds exclusively to the top layer thickness, eliminating the need to model underlying structures. This extraction principle allows accurate top layer measurement without being affected by unknown underlying layers.
Solution Approach 2:
The patent segments the reflectivity spectrum into different frequency components through Fourier Transform analysis. By identifying and analyzing only the primary peak frequency component, the method separates the top layer information from the composite multi-layer response, enabling independent top layer characterization without requiring complete knowledge of the underlying structure stack.
2Measurement precision
If multi-layer models with complete structure information are used, then measurement accuracy can be improved, but measurement time increases due to model optimization requirements
Solution Approach 1:
The patent employs a self-service approach where the Fourier Transform of the reflectivity spectrum automatically generates the thickness information through the primary peak position. This eliminates the need for time-consuming iterative model optimization and parameter fitting, as the top layer thickness can be directly determined from the spectral analysis without requiring complex multi-layer model calculations.
3Measurement precision
If complex multi-layer models are used for accurate measurement, then measurement precision can be improved, but computational complexity increases
Solution Approach 1:
The patent extracts the essential top layer thickness information by taking out only the relevant frequency component (primary peak) from the complex reflectivity spectrum. This simplifies the computational model from a complex multi-layer analysis to a simple single-peak identification problem, dramatically reducing computational complexity while maintaining measurement precision.
Solution Approach 2:
The patent transforms the measurement parameter from the time/spatial domain (reflectivity vs. wavelength) to the frequency domain (FT spectrum vs. optical path difference) through Fourier Transform. This parameter transformation reveals the top layer thickness as a distinct primary peak, simplifying the analysis from complex multi-layer modeling to straightforward peak position measurement.
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
Enables accurate film thickness measurement across a semiconductor sample with high throughput and computational efficiency, independent of the underlying structures' properties, reducing the need for complex multi-layer model optimization.
Implementation Method 1
A first reflectivity spectrum of the sample in the first region is obtained
Implementation Method 2
applying the top-layer model includes performing a Fourier Transform (FT) of the first reflectivity spectrum to obtain an FT spectrum. The first thickness is determined based on a primary peak of the FT spectrum
Data Source
AI summary
A method of film thickness measurement includes illuminating a top layer of a sample in a first region with a broadband illumination beam. The sample includes a substrate and a plurality of semiconductor structures formed between the substrate and the top layer. A first reflectivity spectrum of the sample is obtained in the first region. A first thickness of the top layer in the first region is determined by applying a top-layer model to the first reflectivity spectrum. The top-layer model is substantially unaffected by the plurality of semiconductor structures.