Apodizing Mask Electro-Deposition for Light Transmission Control
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Solution Overview
Problem
Existing apodizing masks in lithography have limited light transmission ratios due to minimum feature resolution size limitations and diffraction issues, resulting in suboptimal performance with maximum transmission around 88% and minimum transmission around 11%, where pitches greater than 9 μm lead to interference from first diffraction orders.
Innovation Solution
An electro-deposition apparatus deposits two partially offset patterns on an apodizing mask, allowing for precise control of light transmission by overlapping fractional portions of the patterns, thereby reducing the effective minimum feature resolution and enhancing the light transmission ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single pattern is deposited with minimum feature resolution size of 1 μm and maximum pitch of 9 μm, then the mask can be manufactured with existing electro-deposition capabilities, but the light transmission ratio is limited to approximately 88% maximum and 11% minimum (8-to-1 ratio)
Solution Approach 1:
The patent divides the mask pattern into multiple separate patterns (first pattern and second pattern) that are deposited at different times and then offset relative to each other. This segmentation allows each pattern to be manufactured within the resolution capabilities of existing electro-deposition equipment while the combined effect achieves higher light transmission ratios by creating smaller effective features through the offset arrangement.
Solution Approach 2:
The patent overlays a second pattern onto the first pattern with a fractional offset, creating a nested structure where the two patterns interpenetrate. This nesting allows the combination of two coarser patterns (each manufacturable with 1 μm resolution) to effectively create finer features (smaller than 1 μm) that would otherwise be impossible to manufacture directly, thereby improving light transmission control.
2Object-affected harmful factors
If the pitch is increased beyond 9 μm to reduce diffraction effects, then fewer diffraction orders encroach on the CCD, but the light transmission ratio deteriorates because larger features cannot achieve the same modulation depth
Solution Approach 1:
The patent changes the effective pitch parameter by offsetting the second pattern relative to the first pattern by a fractional amount. This parameter change allows the system to achieve the benefits of smaller effective pitch (better light transmission control) without actually reducing the physical pitch beyond the 9 μm limit, thereby maintaining diffraction performance while improving light transmission ratio.
3Adaptability or versatility
If the minimum feature resolution is reduced below 1 μm to improve light transmission ratio, then higher transmission ratios can be achieved, but the manufacturing capability exceeds the capabilities of existing electro-deposition apparatus
Solution Approach 1:
Instead of attempting to manufacture sub-1 μm features directly (which exceeds manufacturing capabilities), the patent segments the feature creation into two steps: depositing two separate patterns at manufacturable resolutions, then offsetting them to create the effective sub-1 μm features. This allows the system to achieve fine feature resolution without requiring manufacturing precision beyond existing capabilities.
Solution Approach 2:
The patent introduces an intermediary offset operation between the two deposited patterns. This intermediary step (the fractional offset) acts as a mediator that transforms two coarser patterns into an effective finer pattern, bridging the gap between manufacturable resolution (1 μm) and desired effective resolution (smaller than 1 μm) without requiring direct manufacturing of sub-1 μm features.
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 solution achieves a superior light transmission ratio by allowing gaps in deposition material smaller than the minimum resolution size, reducing minimum transmission to less than 11% and increasing the maximum transmission beyond 88%, effectively controlling diffraction orders and improving mask performance.
Implementation Method 1
Photo-electro forming is one process for producing apodizing masks involving electro-deposition of metal to build-up a film with no glass substrate
Implementation Method 2
Apodizing masks modify the intensity of light, both locally and globally. The performance of apodizing masks is largely defined by the ratio of maximum to minimum light transmission.
Implementation Method 3
diffraction is a significant consideration; ideally, during regular use, only the zeroth order diffraction will be received by a charge-coupled device (CCD), CMOS, or any other type of image sensor
Data Source
AI summary
An electro-deposition apparatus deposits a first pattern of a lithographic mask. The electro-deposition apparatus then deposits a second pattern of the lithographic mask, at least partially offset from the first pattern. The resulting lithographic mask includes a first pattern having a minimum feature resolution size and maximum pitch, and a second pattern having the same minimum feature resolution size and maximum pitch. The first pattern and second pattern are at least partially offset such that a fractional portion of the second pattern is realized and light transmission is more precisely controlled.