Lithography Lens Transmittance Compensation
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Solution Overview
Problem
Current methods for optical proximity correction in projection lithography fail to adequately compensate for the non-uniform amplitude and phase aberrations of the lens system, leading to suboptimal printing results, especially as pattern dimensions approach the optical wavelength limit.
Innovation Solution
A method to characterize and compensate for the complex transmittance function of the projection lens by measuring and analyzing images of test structures, allowing for the extraction of both phase and amplitude transmittance functions, which are then used to correct the mask layout and improve image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional optical proximity correction methods are used, then the lithography process can proceed with standard mask design, but the printing accuracy deteriorates due to uncorrected lens aberrations
Solution Approach 1:
The patent applies preliminary action by measuring and characterizing the lens transmittance function before the actual lithography production. The complex transmittance function (including both amplitude and phase components) is obtained through test structure measurements and stored for subsequent use. This pre-characterization allows the OPC process to compensate for lens aberrations in advance, improving printing accuracy without affecting production workflow.
Solution Approach 2:
The patent implements feedback by using measured lens transmittance data to continuously improve mask design. The complex transmittance function obtained from test measurements feeds into the OPC algorithm, which then generates corrected mask patterns that compensate for the specific lens aberrations. This closed-loop approach ensures that the printing accuracy reflects the actual lens performance.
2Manufacturing precision
If high numerical aperture systems are used to improve resolution, then the printing precision is improved, but lens aberrations and amplitude non-uniformity increase
Solution Approach 1:
The patent applies parameter changes by extracting and utilizing both amplitude and phase components of the complex transmittance function. By measuring these parameters through test structures and incorporating them into the OPC model, the system can compensate for the increased aberrations that come with high NA operation, thereby maintaining printing precision despite using higher numerical aperture lenses.
3Manufacturing precision
If comprehensive lens characterization is performed to improve correction accuracy, then the printing fidelity is improved, but the measurement and analysis complexity increases
Solution Approach 1:
The patent uses test structures as an intermediary to characterize the lens system. Instead of directly measuring complex lens properties, the method projects test patterns through the lens and analyzes the resulting images. These test structures serve as a mediator that translates lens transmittance characteristics into measurable image data, which is then used to extract the complex transmittance function for OPC correction.
Data Source
AI summary
An apparatus and method of compensating for lens imperfections in a projection lithography tool, includes extracting from a diffraction image created by the projection lithography tool a lens transmittance function, and then using the extracted lens transmittance function as a compensator in the lithography projection tool. Another preferred apparatus and method of synthesizing a photomask pattern includes obtaining a phase and an amplitude of a transmittance function of an imaging system; forming a computational model of patterning that includes the transmittance function of the imaging system; and then synthesizing a mask pattern from a given target pattern, by minimizing differences between the target pattern and another pattern that the computational model predicts the synthesized mask pattern will form on a wafer.