Illumination Source Optimization for Lithography DOF
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Solution Overview
Problem
Current methods for determining illumination sources with optimized depth of focus in lithography processes are complex and require extensive simulations, making it difficult to analyze and determine optimal source conditions due to the high number of possible source split conditions and varying DOF values.
Innovation Solution
A method that calculates an optimal correlation ratio or peak variation to identify an illumination source with optimized depth of focus by simulating optimal and defocus correlations, reducing the need for extensive simulations and focusing on peak and correlation variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If extensive FEM simulations are performed for each source condition to determine DOF, then measurement precision is improved, but device complexity and loss of time increase significantly
Solution Approach 1:
The patent extracts the essential characteristics needed for DOF evaluation by calculating only peak intensities and correlation coefficients from simulation data, rather than performing complete FEM simulations. This extraction approach maintains measurement precision while dramatically reducing computational complexity by focusing only on the critical parameters that define DOF performance.
Solution Approach 2:
The patent performs partial simulations that calculate only the necessary parameters (peak intensities and correlation coefficients) required for DOF determination, rather than executing complete FEM simulations. This partial action approach achieves sufficient measurement precision with significantly reduced computational resources and time.
2Measurement precision
If complete FEM simulations with multiple splits are performed for each source condition, then measurement precision is improved, but loss of time increases due to 25-100 simulation times per condition
Solution Approach 1:
The patent extracts only the essential data elements (peak intensities and correlation coefficients) needed for DOF evaluation from simulation results, eliminating the need for complete FEM simulations with multiple splits. This extraction method maintains measurement precision while reducing simulation time from 25-100 times per source condition to a single calculation pass.
Solution Approach 2:
The patent performs partial simulations that compute only the critical parameters for DOF determination rather than executing complete FEM simulations. This approach achieves sufficient measurement precision with dramatically reduced computational time and resources.
3Measurement precision
If multiple simulations are performed to cover CD target specifications, then measurement precision is improved, but device complexity increases due to dose and focus boundary determinations
Solution Approach 1:
The patent extracts the essential characteristics for DOF evaluation by calculating peak intensities and correlation coefficients directly from simulation data, bypassing the complex process of generating complete Bossung curves and determining dose and focus boundaries. This extraction approach maintains measurement precision while significantly simplifying the data collection process.
Solution Approach 2:
The patent performs partial simulations that calculate only the necessary parameters (peaks and correlation coefficients) required for DOF determination, rather than executing complete FEM simulations to cover all CD target specifications. This partial action approach achieves sufficient measurement precision with reduced device complexity.
Data Source
AI summary
A method for determining an illumination source with optimized depth of focus includes the following steps. First, a simulated optimal correlation and a simulated defocus correlation of each illumination source are provided. Second, an optimal peak is determined, a defocus peak is determined, and an optimal correlation slope and a defocus correlation slope are determined. An optimal correlation ratio and a peak variation are calculated. A correlation variation is calculated from the optimal correlation ratio and the defocus correlation ratio. Next, a weighted variation is determined from the peak variation and the correlation variation. An illumination source of a lowest weighted variation among a plurality of the illumination sources is determined to be an illumination source with optimized depth of focus.