Photomask Auxiliary Patterns for Proximity Exposure Resolution
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Solution Overview
Problem
Conventional proximity exposure methods in lithography face challenges in forming fine patterns due to pattern distortion caused by Fresnel diffraction, limiting resolution to around 4-5 μm with a 50 μm gap, and are costly due to the need for high-accuracy lenses in projection exposure methods.
Innovation Solution
A photomask design featuring a translucent substrate with a light blocking member, including a main pattern portion and auxiliary pattern portions that transmit in-phase light to enhance light intensity at the outline of the desired pattern, allowing for improved resolution comparable to projection exposure methods without the need for high-accuracy lenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If proximity exposure is performed with a gap between photomask and exposed body, then production cost is reduced and ease of manufacture is improved, but pattern resolution deteriorates due to Fresnel diffraction distortion
Solution Approach 1:
The patent applies preliminary action by pre-calculating and correcting the pattern design data before photomask fabrication. The correction process anticipates the Fresnel diffraction distortion that will occur during proximity exposure and compensates for it in advance. This allows the use of simple proximity exposure equipment without high-accuracy lenses while still achieving the desired pattern resolution on the exposed body.
Solution Approach 2:
The patent changes the parameters of the pattern design data, specifically adjusting line widths, spacing, and other geometric parameters to compensate for the expected diffraction effects. By modifying these parameters beforehand, the distortion caused by the gap-induced Fresnel diffraction is counteracted, enabling high-resolution pattern formation through low-cost proximity exposure.
2Manufacturing precision
If projection exposure method is used with high-accuracy lens, then pattern resolution is improved to wavelength level, but equipment cost increases substantially
Solution Approach 1:
The patent extracts and removes the need for high-accuracy projection lenses from the exposure system. By taking out this expensive optical component and replacing it with simple proximity exposure equipment, the patent achieves cost reduction while maintaining pattern resolution through computational correction of the pattern design data to compensate for diffraction effects.
3Ease of operation
If gap of 50 μm or more is provided between mask and exposed body, then ease of operation is improved, but pattern size smaller than ten times wavelength cannot be formed
Solution Approach 1:
The patent applies preliminary action by pre-correcting the pattern design data to account for Fresnel diffraction effects that occur with large gaps. This allows operators to maintain a comfortable 50 μm or greater gap between mask and exposed body for ease of operation, while the pre-calculated corrections ensure that fine patterns smaller than ten times the wavelength are still formed with high 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
The proposed photomask design significantly improves resolution in proximity exposure, enabling the formation of fine patterns with high contrast and minimal distortion, similar to projection exposure methods, while reducing costs by eliminating the need for expensive lenses.
Implementation Method 1
auxiliary pattern portions that transmit in-phase light to enhance light intensity at the outline of the desired pattern
Implementation Method 2
pattern distortion caused by Fresnel diffraction
Data Source
AI summary
A photomask includes: a light blocking member provided on a translucent substrate; a main pattern portion provided in a first region corresponding to a desired pattern, being an opening of the light blocking member; and an auxiliary pattern portion provided in a second region surrounding the position corresponding to the desired pattern and along a side constituting an outline portion of the desired pattern, including a plurality of in-phase auxiliary patterns each of which is an opening transmitting in-phase light with light transmitted through the main pattern portion. The in-phase auxiliary pattern is provided at a distance of √(2×n×G×λ) from the side constituting the outline portion of the desired pattern (where G is a gap length between the photomask and the exposed body, λ is a wavelength of the exposure light, and n is a natural number). The exposure light transmitted through the auxiliary pattern portion is projected on an exposed body to form a projection image having light intensity emphasized at the side constituting the outline portion of the desired pattern.