Displacement Talbot Lithography for Surface-Relief Grating Duty Cycle Control
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Solution Overview
Problem
Current methods for manufacturing surface-relief gratings with sub-micron periods for augmented and virtual reality displays are not well-suited for low-cost volume production due to limitations in resolution, reproducibility, and environmental stability, particularly with techniques like electron-beam lithography and holographic exposure systems.
Innovation Solution
The use of displacement Talbot lithography to print surface-relief gratings with varying duty cycles in a layer of photoresist on a substrate, employing a high-resolution grating mask and a variable-transmission grating mask to achieve desired spatial variations in diffraction efficiency, allowing for the formation of gratings with one-dimensional or two-dimensional variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If electron-beam lithography is used to manufacture surface-relief gratings with sub-micron periods, then manufacturing precision is improved, but productivity deteriorates and device complexity increases
Solution Approach 1:
The patent uses photolithography to copy the grating pattern from a master mask onto the photoresist-coated substrate. This optical copying method enables high-volume production while maintaining precision through the use of high-quality photomasks and optimized exposure parameters, eliminating the need for slow electron-beam writing.
Solution Approach 2:
The patent replaces the mechanical electron-beam lithography system with an optical photolithography system. By using light instead of electron beams, the process achieves both high precision and high productivity, as optical systems can expose entire wafer areas simultaneously rather than writing line-by-line.
2Ease of manufacture
If holographic exposure systems are used to manufacture surface-relief gratings, then ease of manufacture is improved, but measurement precision deteriorates due to environmental stability issues
Solution Approach 1:
The patent uses pre-fabricated photomasks with precisely defined grating patterns as templates. The mask patterns are created with high precision beforehand, and then simply copied onto the substrate through photolithography. This preliminary preparation of accurate master patterns eliminates the environmental sensitivity problems of holographic recording while maintaining ease of manufacture.
Solution Approach 2:
The patent introduces a photomask as an intermediary carrier of the grating pattern. Instead of directly recording the pattern onto the photoresist (as in holography), the pattern is first fixed on a stable mask substrate, then transferred optically. This intermediary step isolates the precision requirements from environmental variations during the actual fabrication process.
3Ease of manufacture
If conventional photolithography is used with fixed duty cycle masks, then ease of manufacture is improved, but manufacturing precision deteriorates because it cannot achieve spatial variations in diffraction efficiency
Solution Approach 1:
The patent employs photomasks with spatially varying duty cycles, where different regions of the mask have different transparent-to-opaque ratios. This allows the exposed photoresist to develop with corresponding spatial variations in grating depth or width, thereby achieving non-uniform diffraction efficiency across the grating area while maintaining the simplicity of conventional photolithography processing.
Solution Approach 2:
The patent varies the duty cycle parameter of the mask pattern across different spatial locations. By changing the width ratio of transparent and opaque regions in the mask, the exposure dose received by different areas of the photoresist varies, resulting in gratings with spatially controlled diffraction efficiency without requiring complex process changes.
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 method enables the production of surface-relief gratings with precise spatial variations in diffraction efficiency, enhancing the performance of virtual and augmented reality displays while simplifying the manufacturing process and improving cost-effectiveness.
Implementation Method 1
displacement Talbot lithography to print surface-relief gratings with varying duty cycles in a layer of photoresist on a substrate, employing a high-resolution grating mask
Implementation Method 2
variable-transmission grating mask to achieve desired spatial variations in diffraction efficiency
Implementation Method 3
print surface-relief gratings with varying duty cycles in a layer of photoresist on a substrate
Data Source
AI summary
A method for forming a surface-relief grating with a desired spatial variation of duty cycle in a layer of photoresist includes: providing a first mask bearing a high-resolution grating of linear features, arranging the first mask at a first distance from a substrate, providing a second mask bearing a variable-transmission grating of opaque and transparent linear features that has a designed spatial variation of duty cycle, arranging the second mask at a distance before the first mask such that the linear features of the variable-transmission grating are orthogonal to the linear features of the high-resolution grating, illuminating the second mask while varying the first distance according to displacement Talbot lithography and also displacing the second mask at an angle to its linear features such that there is substantially no component of modulation with the period of the variable-transmission grating in the energy density distribution that exposes the photoresist.