Lithographic Scatterometer Calibration Library for Metrology Speed
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Solution Overview
Problem
Current methods for determining lithographic process parameters are inefficient, requiring significant calculation time due to variations in metrology hardware and material parameters, especially when dealing with multiple scatterometers.
Innovation Solution
A method involving the calculation of calibration spectra for reference patterns without considering apparatus parameters, followed by the calculation of corresponding spectra for target patterns using apparatus-specific parameters, allowing for efficient comparison and derivation of target pattern parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration spectra are calculated for each scatterometer with all hardware parameters, then measurement precision is improved, but calculation time increases significantly
Solution Approach 1:
The patent divides the calibration process into two segments: (1) calculating hardware-independent calibration spectra for reference patterns, and (2) calculating hardware-specific correction factors. This segmentation allows the bulk of the calculation to be done once and reused, reducing total calculation time while maintaining precision for each specific scatterometer.
Solution Approach 2:
The patent performs preliminary calculation of calibration spectra for reference patterns without considering specific hardware parameters. These pre-calculated spectra serve as a foundation that can be quickly adjusted for different scatterometers by only calculating the necessary hardware-specific corrections, rather than recalculating everything from scratch.
2Adaptability or versatility
If library calculations are performed for multiple scatterometers with different parameters, then adaptability is improved, but calculation time increases
Solution Approach 1:
The patent creates a universal calibration library that can be applied across multiple scatterometers. The reference pattern calibration spectra serve as a universal base that can be adapted to different scatterometers by applying hardware-specific correction factors, eliminating the need to create separate complete libraries for each scatterometer type.
Solution Approach 2:
The patent changes the approach from calculating complete hardware-specific libraries to calculating correction factors based on parameter variations. By determining how actual hardware parameters deviate from reference values and applying corresponding corrections to the universal calibration library, the system achieves adaptability to multiple scatterometers with reduced calculation time.
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 significantly reduces calculation time by enabling the efficient determination of lithographic process parameters, facilitating faster data processing and improved accuracy in metrology hardware-specific conditions.
Implementation Method 1
a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured
Implementation Method 2
by comparing the properties of the beam before and after it has been reflected or scattered by the substrate
Data Source
AI summary
In a method for determining a structure parameter of a target pattern, a first series of calibration spectra are determined from at least one reference pattern, each spectra being determined using a different known value of at least one structure parameter of the respective reference pattern. The first series of calibration spectra does not take into account parameters of an apparatus used to produce the reference pattern. A representation of each of the first series calibration spectra is stored in a central library. A second series of calibration spectra corresponding to at least one of the stored spectra for a target spectrum is determined using the parameters of the apparatus for measuring the target spectrum. A measured target spectrum is produced by directing a beam of radiation onto the target pattern. The measured target spectrum and the second series of calibration spectra are compared, where this comparison is used to derive a value for the structure parameter of the target pattern.