Lithographic Process Optimization via Bandwidth Speckle Control
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Solution Overview
Problem
Current lithographic processes face challenges in achieving precise pattern reproduction with features smaller than the classical resolution limit, particularly due to speckle interference effects that lead to local dose variations and non-uniform exposure, affecting pattern fidelity and critical dimension uniformity.
Innovation Solution
A method is introduced to optimize the lithographic process by computing a multi-variable cost function that includes design variables and radiation bandwidth, adjusting these variables to satisfy a speckle characteristic within a specification while maintaining image contrast, involving the reconfiguration of the lithographic process to reduce speckle contrast through changes in radiation bandwidth and pulse duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the radiation bandwidth is increased to reduce speckle contrast, then speckle interference is reduced, but image contrast deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the radiation bandwidth as a controllable parameter. The system modifies the spectral width of the illumination source to optimize the trade-off between reducing speckle contrast and maintaining image contrast, treating bandwidth as a tunable parameter rather than a fixed property
Solution Approach 2:
The system implements dynamics by making the radiation bandwidth adjustable and reconfigurable during operation. The illumination source can dynamically change its spectral characteristics based on process requirements, transitioning between narrowband and wideband modes to balance speckle reduction with image quality preservation
2Object-affected harmful factors
If the bandwidth is increased to reduce speckle, then speckle contrast decreases, but pattern fidelity deteriorates
Solution Approach 1:
The system uses parameter changes by adjusting the radiation bandwidth to control speckle effects while preserving pattern fidelity. By optimizing the bandwidth parameter, the system reduces speckle-induced local dose variations without compromising the accuracy of pattern reproduction
Solution Approach 2:
The patent employs feedback mechanisms to monitor and adjust the radiation bandwidth based on observed speckle characteristics and pattern quality metrics. The system uses cost function evaluation to provide feedback on the trade-off between speckle reduction and pattern fidelity, enabling iterative optimization
3Reliability
If multiple design variables are optimized together, then overall process performance improves, but computational complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the multi-variable optimization problem into manageable components. The cost function is structured to evaluate different design variables (bandwidth, pulse duration, illumination parameters) in a systematic way, allowing the complex optimization to be broken down into smaller computational tasks
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 effectively reduces speckle contrast and improves image quality by maintaining image contrast within desired ranges, enhancing critical dimension uniformity and pattern fidelity, even with features below the classical resolution limit.
Implementation Method 1
a radiation source configured to generate radiation having a wavelength of 193 nanometers (nm)
Implementation Method 2
speckle interference effects that lead to local dose variations and non-uniform exposure
Data Source
AI summary
A method for improving a lithographic process of imaging a portion of a design layout onto a substrate using a lithographic apparatus. The method includes computing a multi-variable cost function that is a function of: (i) a plurality of design variables that affect characteristics of the lithographic process and (ii) a radiation bandwidth of a radiation source of the lithographic apparatus; and reconfiguring one or more of the characteristics (e.g., EPE, image contrast, resist, etc.) of the lithographic process by adjusting one or more of the design variables (e.g., source, mask layout, bandwidth, etc.) until a termination condition is satisfied. The termination condition includes a speckle characteristic (e.g., a speckle contrast) maintained within a speckle specification associated with the radiation source and also maintaining an image contrast associated with the lithographic process within a desired range. The speckle characteristic being a function of the radiation bandwidth.