Spectrometer Model Parameter Optimization via Inverse Analysis

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Solution Overview

Problem

Current methods for modeling spectrometer data are inefficient due to the difficulty in selecting free and fixed parameters, leading to unstable matching processes and errors, as they do not adequately account for the impact of noise and errors in the measurement signal on the model.

Innovation Solution

A method that involves setting initial parameter values, generating simulated spectra, and using an inverse model to adjust parameters while maintaining fixed values, with differences used as a figure of merit for selecting free and fixed parameters, and applying this process iteratively to optimize the parameter selection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If many parameters are varied freely to generate modeled spectra for matching, then the model can accommodate more physical realities, but the matching process becomes extremely time consuming and unstable

Engineering Contradiction:
Improvemodel flexibilityVSAvoidmatching speed
Core Design Contradiction:
Adaptability or versatilityVSProductivity

Solution Approach 1:

The patent applies parameter changes by systematically varying the number and type of free parameters in the model. It evaluates different parameter configurations (e.g., varying thickness, refractive index, or other physical parameters) to determine the optimal balance between model flexibility and matching efficiency. This allows the system to adapt the model complexity based on the specific measurement requirements while maintaining acceptable matching speeds.

Inventive Principle:
Principle #35Parameter changes

2Adaptability or versatility

If many parameters are varied freely in the model, then more physical realities can be captured, but the matching process becomes erroneous due to multiple parameter combinations producing similar spectra

Engineering Contradiction:
Improvemodel flexibilityVSAvoidparameter determination accuracy
Core Design Contradiction:
Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent implements feedback mechanisms by continuously evaluating the matching results and using correlation matrices to assess parameter independence. The system feeds back the correlation information to guide further parameter selection, adjusting which parameters to treat as free versus fixed based on their mutual dependencies and impact on measurement accuracy. This iterative feedback loop prevents erroneous parameter determination while maintaining model flexibility.

Inventive Principle:
Principle #23Feedback

Solution Approach 2:

The patent introduces correlation matrices as intermediary tools to analyze the relationships between parameters. These matrices serve as mediators that quantify how changes in one parameter affect others, enabling the system to make informed decisions about parameter freedom. The correlation matrix acts as an intermediary that translates complex parameter interactions into actionable guidance for model configuration.

Inventive Principle:
Principle #24Intermediary (Mediator)

3Productivity

If parameters are fixed to reduce matching time, then productivity improves, but it becomes difficult to determine which parameters should be free and which should be fixed

Engineering Contradiction:
Improvematching speedVSAvoidparameter selection complexity
Core Design Contradiction:
ProductivityVSDevice complexity

Solution Approach 1:

The patent applies self-service by enabling the system to automatically determine optimal parameter configurations through automated evaluation of correlation matrices and matching performance. Rather than requiring manual expert judgment to select free versus fixed parameters, the system self-evaluates different parameter settings and autonomously identifies the configuration that balances model flexibility with matching speed and accuracy. This automated self-service approach reduces the complexity of parameter selection while maintaining high productivity.

Inventive Principle:
Principle #25Self-service

4Device complexity

If current parameter selection methods are used, then the process is simplified, but it does not account for the impact of noise and measurement errors on the model

Engineering Contradiction:
Improveparameter selection simplicityVSAvoidmodel reliability
Core Design Contradiction:
Device complexityVSReliability

Solution Approach 1:

The patent applies preliminary action by pre-evaluating the impact of noise and measurement errors on parameter determination before the actual matching process. The system performs preliminary analyses using correlation matrices and sensitivity studies to anticipate how noise will affect different parameter selections. This preliminary assessment guides the choice of free versus fixed parameters in a way that proactively accounts for noise and error impacts, improving model reliability before measurements are even taken.

Inventive Principle:
Principle #10Preliminary action

Data Source

PatentUS8868387B2Method of optimizing a model, a method of measuring a property, a device manufacturing method, a spectrometer and a lithographic apparatus
Publication Date: 2014.10.21 ASML NETHERLANDS BV
  • US8868387B2 patent drawing
  • US8868387B2 patent drawing
  • US8868387B2 patent drawing

AI summary

A set of parameters used in a model of a spectrometer includes free parameters and fixed parameters. A first set of values for the parameters is set and the model is used to generate a first spectrum. A value of one of the fixed parameters is changed and a second spectrum is generated. An inverse of the model of the spectrometer is then applied to the second spectrum to generate a set of values for the parameters, the values being the same as the first set of values except for one or more of the free parameters. If the free parameter has significantly changed the fixed parameter is designated a free parameter.