Broadband Interferometer Autocorrelation Film Thickness
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Solution Overview
Problem
Existing methods for determining properties of a sample using broadband interferometry require information about the complex surface structure, which is not always available, and are inefficient in determining film thickness and refractive index independently of the sample's height.
Innovation Solution
The method involves autocorrelating the correlogram to calculate an autocorrelogram, which allows for the determination of film thickness and refractive index independently of the sample's height, and uses a look-up table of reference autocorrelograms to quickly match and determine sample properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cross-correlation with model signal is used to determine surface height, then measurement precision is improved, but device complexity increases due to requirement of complex surface structure information
Solution Approach 1:
The patent extracts only the necessary autocorrelation information from the interferogram, eliminating the need for complex surface structure information. By applying autocorrelation to the interferogram, the method determines film thickness and refractive index without requiring knowledge of the complex surface structure, thus reducing device complexity while maintaining measurement precision.
2Measurement precision
If traditional broadband interferometry is used to determine film properties, then measurement capability is maintained, but productivity decreases due to inefficiency in determining thickness and refractive index independently of sample height
Solution Approach 1:
The patent applies autocorrelation as a preliminary processing step to the interferogram before determining film properties. This preliminary action transforms the interferogram into an autocorrelation function that directly provides information about film thickness and refractive index independent of sample height, significantly improving determination efficiency while maintaining measurement capability.
3Measurement precision
If sample height information is required for film thickness determination, then measurement completeness is improved, but ease of operation worsens due to additional measurement requirements
Solution Approach 1:
The patent extracts film thickness and refractive index information directly from the autocorrelation of the interferogram, eliminating the need to separately measure or know the sample height. This extraction approach maintains measurement completeness for film properties while greatly simplifying the operation by removing the additional height measurement requirement.
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 provides a robust and fast method for determining sample properties by simplifying the process and reducing the need for height information, enabling efficient thickness and refractive index determination.
Implementation Method 1
a detector for receiving an interference signal from the reflected reference beam from the reference reflector and the reflected measurement beam from the surface of the sample
Implementation Method 2
a beam splitter for splitting the illumination beam in a reference beam for reflection on a reference reflector and a measurement beam for reflection on a surface of the sample
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
The invention relates to determining a property of a sample from a correlogram obtainable by scanning of a surface of the sample through a focal plane of an objective using broad-band interferometry. The correlogram may be displaying interference radiation intensity as a function of the scanning distance from the surface. The correlogram may be correlated with a secondary correlogram to obtain a cross correlogram or with the same correlogram to obtain an autocorrelogram. A property of the sample may be determined from the auto or cross correlogram.