Photomask Alignment Mark Segmentation for Shadow Effect
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Solution Overview
Problem
In photolithography processes for integrated circuit manufacturing, alignment marks are prone to shadow effects during exposure, leading to underexposure and residual photoresist issues, which increase processing time and reduce throughput due to the need for multiple exposure steps to clean out shadow regions.
Innovation Solution
A photomask design incorporating a shot region and an alignment mark pattern region with a clean-out, block, and dummy pattern region allows for a single exposure process to clean out photoresist residuals and form dummy patterns, protecting alignment marks from being patterned or damaged.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mask blades cover a portion of the photoresist layer over the alignment marks during exposure process, then the alignment marks are protected from being patterned, but shadow effect causes underexposure and photoresist residual around the alignment marks
Solution Approach 1:
The alignment mark region on the photomask is divided into three distinct segments: a block region (to protect the alignment mark), a clean-out region (to eliminate shadow effect residuals), and a dummy pattern region (to maintain pattern density). This segmentation allows each region to perform its specific function independently, resolving the contradiction between protection and residual elimination.
Solution Approach 2:
Different regions of the alignment mark region on the photomask are assigned different optical properties: the block region is opaque to block light and protect the alignment mark, the clean-out region is transparent to allow light exposure and eliminate shadow residuals, and the dummy pattern region has intermediate properties to maintain pattern density. This local differentiation resolves the contradiction by applying different qualities to different locations.
2Manufacturing precision
If multiple exposure processes are performed to clean out the shadow region around the alignment mark, then photoresist residual is removed, but processing time is increased and throughput is decreased
Solution Approach 1:
The block region, clean-out region, and dummy pattern region are merged into a single integrated alignment mark region on the photomask. This allows all three functions (protection, cleaning, and pattern density maintenance) to be achieved in one exposure process, eliminating the need for multiple sequential exposure steps and thereby increasing throughput while maintaining manufacturing precision.
Solution Approach 2:
The alignment mark region on the photomask is designed to perform multiple functions simultaneously: the block region protects the alignment mark, the clean-out region eliminates shadow residuals, and the dummy pattern region maintains pattern density. This multi-functionality allows a single exposure process to achieve what previously required multiple steps, resolving the contradiction between precision and productivity.
3Manufacturing precision
If the alignment mark region is fully exposed to pattern the wafer, then pattern density is maintained, but the alignment mark is patterned or damaged
Solution Approach 1:
The alignment mark region is segmented into a block region and a dummy pattern region. The block region remains opaque to protect the alignment mark from patterning, while the dummy pattern region is transparent to allow light exposure and maintain pattern density in the surrounding area. This segmentation resolves the contradiction by separating the protection function from the pattern density function.
Solution Approach 2:
The dummy pattern region acts as an intermediary between the block region and the rest of the wafer. It provides a transition zone that maintains pattern density and facilitates light exposure in the surrounding area without compromising the protected alignment mark in the block region. This intermediary structure resolves the contradiction by mediating between protection and pattern density requirements.
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 reduces processing time and steps, increases throughput by enabling simultaneous cleaning and patterning of alignment marks, while maintaining pattern density and step height similarity to the main die region.
Implementation Method 1
the block region is used for blocking a light in order to protect the alignment mark on the wafer from being patterned during the exposure process
Implementation Method 2
the clean-out region is used for cleaning out a shadow region around the alignment mark on the wafer due to a shadow effect
Implementation Method 3
the shadow effect happens to transform a portion of the photoresist layer covered by the mask blades near the edge of the mask blades into a shadow region
Implementation Method 4
photolithography process is used to transfer patterns from a photo mask having customized circuit patterns to thin films formed on a wafer
Data Source
AI summary
A photomask for defining a photoresist layer formed on a wafer having at least an alignment mark region, wherein each alignment mark region has an alignment mark. The photomask comprises a shot region and an alignment mark pattern region. The alignment mark pattern region has a profile equal to the profile of the alignment mark region on the wafer. Further, the alignment mark pattern region comprises a block region, a clean-out region and a dummy pattern region. The position of the block region in the alignment mark pattern region corresponds to the relative position of the alignment mark in the alignment mark region. The clean-out region is adjacent to one side of the block region and the dummy pattern region is adjacent to another side of the block region.