Pupil Plane Function Modifies Wavefront Phase for Extended Depth of Focus
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Solution Overview
Problem
Optical lithography systems face challenges in increasing resolution while maintaining depth of focus and controlling focus-related aberrations, leading to increased costs and complexity, particularly as numerical aperture increases, which affects the manufacturing and alignment of reticles and wafers.
Innovation Solution
The implementation of a pupil plane function that modifies the wavefront imaged by the optical lithographic system, allowing for extended depth of focus and improved alignment tolerances, enabling higher numerical apertures without reducing depth of focus, and optimizing the system response to match the spatial frequency content of the desired aerial image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If numerical aperture is increased to improve resolution, then resolution is improved, but depth of focus decreases with the square of the increase in NA
Solution Approach 1:
The patent introduces a pupil plane function that operates in the Fourier transform domain (pupil plane) rather than directly in the image plane. This transforms the problem from a spatial domain constraint to a frequency domain solution, where phase modulation of the optical transfer function extends the depth of focus while preserving high numerical aperture resolution.
Solution Approach 2:
The patent modifies the optical transfer function by applying a pupil plane function that changes the phase parameter of the imaging system. This phase modification in the pupil plane creates an extended depth of focus effect without altering the numerical aperture or wavelength parameters, thereby resolving the contradiction between resolution and depth of focus.
2Manufacturing precision
If wavelength is reduced to improve resolution, then resolution is improved, but depth of focus decreases linearly with the decrease in wavelength
Solution Approach 1:
The patent changes the phase parameter of the optical transfer function through pupil plane modulation, which extends depth of focus independent of wavelength. This allows the system to maintain both short wavelength for high resolution and extended depth of focus through phase-based optical path modification rather than geometric constraints.
3Manufacturing precision
If numerical aperture is increased, then resolution is improved, but assembly tolerances and alignment requirements become more stringent
Solution Approach 1:
The patent applies a pupil plane function that pre-compensates for focus variations and alignment errors by modifying the optical transfer function phase. This preliminary correction in the frequency domain counteracts the stringent tolerance requirements that would otherwise result from high numerical aperture imaging, making assembly and alignment more feasible.
4Length of stationary object
If depth of focus is extended through pupil plane function, then depth of focus is extended, but optical system complexity increases
Solution Approach 1:
The patent introduces a pupil plane function as an intermediary element in the optical path that mediates between the objective lens and the image plane. This intermediary modifies the optical transfer function phase to extend depth of focus while maintaining a relatively simple overall optical structure, avoiding the need for complex multi-element lens assemblies.
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 maintains the resolution of the optical lithography system with relaxed assembly tolerances, increases the usable field of view, and enhances throughput by allowing for larger misfocus ranges and increased numerical apertures, reducing the need for precise alignment and reducing manufacturing costs.
Implementation Method 1
a pupil plane function to form an aerial image of the reticle proximate to the photoresist. The pupil plane function modifies an optical transfer function of the imaging lens such that a desired aerial image is formed over the extended depth of focus
Data Source
AI summary
An optical lithography system that has extended depth of focus exposes a photoresist coating on a wafer, and includes an illumination sub-system, a reticle, and an imaging lens that has a pupil plane function to form an aerial image of the reticle proximate to the photoresist. The pupil plane function provides the extended depth of focus such that the system may be manufactured or used with relaxed tolerance, reduced cost and/or increased throughput. The system may be used to form precise vias within integrated circuits even in the presence of misfocus or misalignment.