Talbot Lithography Periodic Pattern Printing Depth of Field
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Solution Overview
Problem
Current photolithographic techniques, such as Talbot lithography, face challenges with limited depth of field and sensitivity to substrate positioning, especially when printing high-resolution periodic patterns on non-flat surfaces or thick photoresist layers, and require complex illumination systems or laser sources with variable wavelengths.
Innovation Solution
A method involving multiple sub-exposures with controlled separation changes between the mask and substrate, where each sub-exposure's separation is adjusted by a fraction of the Talbot distance, ensuring the average intensity distribution is independent of initial separation and surface flatness, allowing for uniform and reproducible printing of periodic patterns without the need for complex illumination systems or precise substrate displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If Talbot lithography is used to print high-resolution periodic patterns, then resolution is improved, but depth of field is limited and sensitivity to substrate positioning increases
Solution Approach 1:
The patent applies periodic action by performing multiple sub-exposures at different longitudinal positions separated by Talbot distances. The substrate is exposed at N different positions along the propagation direction, where each position corresponds to a different Talbot plane. This periodic sampling of the light field at intervals of Talbot distance creates an averaged intensity distribution that is independent of the initial separation distance, thereby achieving large depth of field while maintaining high resolution periodic pattern printing
2Manufacturing precision
If Talbot lithography is used to print high-resolution periodic patterns, then resolution is improved, but sensitivity to substrate positioning and surface flatness increases
Solution Approach 1:
The patent performs N sub-exposures at different longitudinal positions separated by Talbot distances, creating an averaged intensity distribution that eliminates sensitivity to initial separation distance and surface flatness variations
Solution Approach 2:
The patent changes the longitudinal position parameter of the substrate relative to the mask across multiple sub-exposures. By varying the separation distance in discrete steps corresponding to Talbot distances, the system transforms a positioning-sensitive single-exposure process into a positioning-insensitive multi-exposure process, where the final pattern is an average over multiple positions
3Manufacturing precision
If conventional photolithographic systems are used to print high-resolution patterns, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex optical illumination systems with a simpler approach based on the Talbot effect. Instead of using complex condenser lenses, apertures, and illumination optics to achieve high-resolution printing, the system uses self-imaging properties of periodic masks illuminated by collimated light, leveraging the natural formation of Talbot planes at regular intervals
Solution Approach 2:
The periodic mask structure serves itself by naturally forming self-images at Talbot planes without requiring external optical elements. The diffracted light orders automatically interfere to recreate the mask pattern at regular intervals, eliminating the need for complex illumination and imaging optics
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 enables high-resolution, uniform, and reproducible printing of periodic patterns with a large depth of field, using a simple laser source and minimizing feature size variations, while maintaining image contrast and resolution.
Implementation Method 1
When a periodic pattern defined in a mask is illuminated with a collimated beam of monochromatic light, diffraction orders in the transmitted light-field reconstruct 'self-images' of the pattern at regular distances from the mask in so-called Talbot planes.
Implementation Method 2
the light-field transmitted by the mask forms Talbot image planes separated by a Talbot distance
Data Source
Figure 1
Figure 2~2b
Figure 3
AI summary
A method for printing a periodic pattern of features into a photosensitive layer, which includes providing a mask bearing a periodic pattern, providing a substrate bearing the photosensitive layer, arranging the substrate substantially parallel to the mask, forming a beam of collimated monochromatic light for illuminating said mask pattern so that the light-field transmitted by the mask forms Talbot image planes separated by a Talbot distance, and performing N sub- exposures of the mask with said beam and changing the separation between sub-exposures so that the relative separation during the ith sub-exposure with respect to that during the first sub-exposure is given by (mi + ni/N) times the Talbot distance, and exposing the mask pattern to the same energy density of illumination for each sub-exposure, wherein the period is selected in relation to the wavelength so that only the zeroth and first diffraction orders are transmitted by the mask.