Photolithography Focus Error Correction via Inter-Field Mapping
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Solution Overview
Problem
Conventional photolithography systems face challenges in accurately correcting for focus errors, particularly due to topographical differences, warping, and tilting of microelectronic substrates, which can impact the precision and yield of semiconductor fabrication.
Innovation Solution
The implementation of inter-field and intra-field offset corrections, using focus error maps derived from phase-shift reticles and scatterometry, to adjust the substrate support's position and improve focus tolerance, with mathematical models capturing these corrections to account for substrate warpage and tilting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If higher numerical aperture (NA) photolithography systems are used to improve resolution, then resolution is improved, but focus budget is reduced and focus control precision requirements increase
Solution Approach 1:
The system performs preliminary focus error measurements using scatterometry across the substrate surface before actual photolithography exposure. Focus error maps are generated in advance to identify and correct focus deviations, allowing the main exposure process to proceed with pre-corrected focus parameters, thus meeting the stringent focus control requirements of high NA systems
Solution Approach 2:
The system implements a feedback mechanism where focus error measurements from scatterometry are continuously fed back to adjust exposure parameters. The measured focus errors are used to generate correction maps that are applied in real-time during the photolithography process, creating a closed-loop control system that maintains the required focus precision
2Manufacturing precision
If conventional focus correction methods are used, then general focus errors are addressed, but substrate-specific errors from topography, warping, and tilting are not adequately corrected
Solution Approach 1:
The system transitions from uniform focus correction to location-specific focus correction by generating focus error maps that capture local variations across the substrate surface. Each region of the substrate receives customized focus adjustments based on its specific topographical characteristics, warping patterns, and tilting angles, allowing precise correction of substrate-specific errors while maintaining overall focus quality
Solution Approach 2:
The system performs preliminary mapping of substrate topography, warping, and tilting characteristics using scatterometry before the actual exposure process. This advance characterization allows the system to pre-calculate and apply location-specific focus corrections for each region of the substrate, ensuring that substrate-specific errors are addressed before they affect manufacturing 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 reduces focus error variance, enhancing product yields by specifically addressing substrate-related focus errors, with observed decreases in focus error variance by 18% in the X-axis and 9% in the Y-axis directions.
Implementation Method 1
The semiconductor wafer is then exposed to a pattern of light that chemically modifies a portion of the photoresist incident to the light
Implementation Method 2
The process further includes removing one of the incident portion or the non-incident portion from the surface of the semiconductor wafer with a chemical solution (e.g., a 'developer')
Data Source
AI summary
Several embodiments of photolithography systems and associated methods of focus correction are disclosed herein. In one embodiment, a method for characterizing focus errors in a photolithography system includes placing a microelectronic substrate onto a substrate support of the photolithography system. The microelectronic substrate is divided into a plurality of fields individually partitioned into a plurality of regions. The method also includes developing a raw focus error map that has a focus error corresponding to the individual regions of the plurality of fields and deriving at least one of an inter-field focus error map and an intra-field focus error map based on the raw focus error map. The inter-field focus error map has an inter-field focus error corresponding to the individual fields, and the intra-field focus error map has an intra-field focus error corresponding to the individual regions.