Talbot Interference Pattern Formation Without Projection Optics
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Solution Overview
Problem
Current pattern formation methods using Talbot interference in photolithography face challenges in achieving high accuracy and resolution due to limitations in the projection optical system, particularly with the miniaturization of patterns and the difficulty in transferring fine features without defects.
Innovation Solution
A pattern formation method and exposure apparatus that utilize a mask with periodically arranged light transmitting portions, where the distance between the mask and substrate, wavelength of illumination light, pitch of light transmitting portions, and numerical aperture of the optical system satisfy specific conditions, allowing for Talbot interference to generate high-resolution patterns without the need for a projection optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a mask with repetitive pattern is irradiated with light to form fine patterns using Talbot interference, then pattern resolution is improved, but pattern accuracy deteriorates due to high-order diffracted light interference
Solution Approach 1:
The patent converts the harmful effect of high-order diffracted light interference into a beneficial effect by intentionally utilizing Talbot interference to form the desired fine pattern. The self-imaging effect at specific distances transforms what would normally be noise into the useful pattern structure, achieving high resolution without complex projection optics
Solution Approach 2:
The patent controls the distance between mask and substrate to satisfy specific mathematical relationships (d = nλ/2 for self-imaging conditions), where n is an integer, λ is wavelength. By precisely controlling this parameter, the system achieves optimal pattern formation while suppressing unwanted interference effects
2Manufacturing precision
If traditional projection optical systems are used for pattern transfer, then pattern accuracy can be maintained, but device complexity and manufacturing difficulty increase due to miniaturization requirements
Solution Approach 1:
The patent extracts and eliminates the complex projection optical system from the lithography apparatus, replacing it with a direct Talbot interference-based pattern transfer method. By removing the projection lens system, the patent simplifies the overall device while maintaining pattern transfer capability through near-field diffraction effects
Solution Approach 2:
The patent introduces Talbot interference as an intermediary mechanism between the mask and substrate. Instead of direct optical projection, the system uses the self-imaging property of periodic structures at specific distances to transfer patterns, acting as a natural intermediary that simplifies the optical path
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 the formation of highly accurate and defect-reduced patterns with improved resolution, overcoming the limitations of traditional methods by blurring high-order diffracted light interference patterns and maintaining contrast, thus enhancing pattern transfer accuracy and reducing dimensional errors.
Implementation Method 1
when a mask having a repetitive pattern is irradiated with light, a phenomenon called Talbot interference (Talbot effect) occurs. In Talbot interference, an image of a pattern is periodically generated along a traveling direction of light.
Implementation Method 2
blurring high-order diffracted light interference patterns
Data Source
AI summary
According to one embodiment, According to one embodiment, a pattern formation method includes disposing a mask and a substrate separately from each other, the mask having a plurality of light transmitting portions arranged periodically. The method includes irradiating the mask with illumination light emitted from an optical part to irradiate the substrate with at least a part of the illumination light transmitted through the light transmitting portions. a distance d between the mask and the substrate, a wavelength λ of the illumination light, a pitch p of an arrangement of the light transmitting parts, a numerical aperture NAi of the optical part, and at least one natural number n satisfy the following. p≧2λ, (np2/λ)−α≦d≦(np2/λ)+α, α=p2(2λ) and λ/(8np)≦NAi<λ/(2np).