Lithographic Apparatus Illumination Optimization
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Solution Overview
Problem
Current lithographic processes face challenges in optimizing multiple imaging parameters simultaneously due to high computational loads and sub-optimal settings that can affect one imaging metric adversely, making it difficult to achieve a globally improved set of settings for complex patterns.
Innovation Solution
A method involving a controllable illumination system and projection system that selects features from a pattern, determines optimal illumination and projection settings, and adjusts phase and polarization to optimize imaging, using a programmable array of micro-mirrors and diffractive optical elements to generate desired illumination modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional illumination and fixed projection settings are used, then the lithographic process is simple and fast, but imaging precision and pattern quality deteriorate for complex patterns
Solution Approach 1:
The patent applies dynamics by making the illumination system programmable and adjustable during operation. The illumination mode can be dynamically changed to match different pattern requirements, and the projection settings can be adjusted based on the specific features being imaged. This dynamic adaptability allows the system to optimize imaging precision for complex patterns without being locked into fixed settings.
Solution Approach 2:
The patent implements parameter changes by varying illumination parameters (such as illumination angle, numerical aperture, and illumination mode) and projection parameters (such as focus and exposure dose) to optimize imaging for different pattern features. The system can change these parameters between exposures or even during scanning to maintain optimal imaging conditions for varying pattern complexities.
2Manufacturing precision
If multiple imaging parameters are optimized simultaneously, then global imaging quality improves, but computational load increases significantly
Solution Approach 1:
The patent applies segmentation by dividing the pattern into multiple features or regions and optimizing illumination and projection settings for each segment independently or in groups. This allows the computational optimization to be performed on smaller subsets rather than the entire pattern at once, reducing the overall computational load while still achieving global imaging quality improvement through coordinated optimization of multiple segments.
Solution Approach 2:
The patent implements preliminary action by pre-calculating optimal illumination and projection settings for different pattern features before actual imaging. The system can pre-determine the best parameters for various pattern types and store them for rapid retrieval during production, avoiding the need to perform complex computational optimization in real-time during the imaging process.
3Measurement precision
If custom diffractive optical elements are designed and manufactured, then illumination mode precision improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies copying by using a programmable array of micro-mirrors to replicate the function of custom diffractive optical elements. Instead of manufacturing physical DOE components with precise microlens arrays, the system uses software-controlled micro-mirrors to dynamically create the desired illumination patterns. This virtual copying approach achieves the same illumination mode precision without the complexity and cost of custom optical element manufacturing.
Solution Approach 2:
The patent implements mechanics substitution by replacing the mechanical/optical system of custom diffractive optical elements with a programmable electronic control system. The micro-mirror array, controlled by electronic signals, substitutes for the fixed optical structure of DOEs, allowing flexible reconfiguration of illumination modes through software rather than requiring physical manufacturing changes.
4Manufacturing precision
If focus errors are reduced from 30-40 nm to 10 nm, then feature placement accuracy improves, but process sensitivity increases
Solution Approach 1:
The patent applies feedback by implementing a closed-loop optimization system that measures imaging results and adjusts illumination and projection parameters accordingly. The system can detect focus errors and placement inaccuracies, then automatically adjust parameters to correct these errors, maintaining high precision while compensating for process variations that would otherwise cause sensitivity issues.
Solution Approach 2:
The patent implements beforehand cushioning by optimizing the process window and creating margins for error in the illumination and projection settings. The system determines parameter ranges that provide robustness against variations, so that even with reduced focus errors, the process remains tolerant to normal manufacturing variations. This cushioning approach prevents excessive sensitivity while maintaining high precision.
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 allows for significant improvements in feature placement accuracy, focus, and pattern asymmetry, reducing focus errors from 30-40 nm to 10 nm, and providing a broader process window for imaging complex patterns.
Implementation Method 1
A diffractive optical element (DOE) can be used that is custom made and placed in the illumination system... An arrangement may be used to enable any desired illumination mode to be generated using a programmable array of individually-adjustable micro-mirrors.
Implementation Method 2
a controllable projection system arranged to project an image of the patterning device onto the substrate as a patterned beam of radiation
Implementation Method 3
It has been proposed to immerse the substrate in the lithographic projection apparatus in a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the final element of the projection system and the substrate. The point of this is to enable imaging of smaller features since the exposure radiation will have a shorter wavelength in the liquid. (The effect of the liquid may also be regarded as increasing the effective numerical aperture (NA) of the system...)
Implementation Method 4
A diffractive optical element (DOE) can be used that is custom made and placed in the illumination system...
Data Source
AI summary
A method of optimizing a lithographic process for imaging a pattern, including a plurality of features, onto a substrate using a lithographic apparatus, the lithographic apparatus having a controllable illumination system to illuminate a patterning device and a controllable projection system to project an image of the patterning device onto the substrate, the method including selecting a feature from the plurality of features, determining an illumination setting for the illumination system to optimize imaging of the selected feature, and determining a projection setting for the projection system to optimize imaging of the selected feature taking account of the illumination setting.