Lithographic Double Exposure Overlay Control via Local Alignment Mark
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Solution Overview
Problem
Double exposure technology in lithographic apparatuses faces challenges with overlay requirements due to the alignment of first and second exposures using the same mark, leading to reduced precision and increased error, especially when dealing with opaque hard mask layers that introduce weak signals and residual topography.
Innovation Solution
The method involves projecting a main mark on a base layer for alignment, followed by transferring a first pattern and local mark pattern to a pattern receiving layer, and then using the local mark for precise alignment of a second pattern, allowing for improved overlay control and reduced error by separating the alignment processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the same mark is used for aligning both first and second exposures, then the alignment process is simplified, but the measurement precision and overlay control are reduced due to accumulated position measurement errors
Solution Approach 1:
The alignment mark is segmented into two distinct parts: a global alignment mark for coarse alignment and a local alignment mark for fine overlay alignment. This segmentation allows the first exposure to use the global mark while the second exposure uses the local mark, preventing error accumulation and improving measurement precision without significantly increasing process complexity
Solution Approach 2:
A local alignment mark is introduced as an intermediary element that is formed during the first exposure and then used for aligning the second exposure. This intermediary mark serves as a reference that eliminates the need to repeatedly measure the same global mark, thereby improving overlay control precision
2Manufacturing precision
If double exposure technology is used to create assembled patterns with smaller critical dimensions, then the manufacturing precision is improved, but the overlay requirements become more stringent and difficult to achieve
Solution Approach 1:
The alignment mark system is segmented into global and local components, where the local mark is specifically designed to provide high-precision reference for the second exposure. This enables reliable overlay alignment even when manufacturing features with critical dimensions below the single-exposure limit
Solution Approach 2:
The local alignment mark is created as a copy during the first exposure process itself, ensuring that it is perfectly aligned with the first pattern. This copied reference mark then enables precise alignment of the second exposure, maintaining reliability even for sub-CD features
3Device complexity
If alignment is performed on residual topography of opaque hard mask layers, then the alignment can be done on the same mark, but the signal strength is weakened affecting overlay control
Solution Approach 1:
The local alignment mark is formed in advance during the first exposure, creating a strong, clear reference feature before the second exposure. This preliminary creation of the alignment mark ensures strong signal strength for overlay measurement, avoiding the weakness associated with residual topography of opaque layers
Data Source
AI summary
A device manufacturing method includes a transfer of a pattern from a patterning device onto a substrate. The device manufacturing method further includes transferring a pattern of a main mark to a base layer for forming an alignment mark; depositing a pattern receiving layer on the base layer; in a first lithographic process, aligning, by using the main mark, a first mask that includes a first pattern and a local mark pattern, and transferring the first pattern and the local mark pattern to the pattern receiving layer; aligning, by using the local mark pattern, a second mask including a second pattern relative to the pattern receiving layer; andin a second lithographic process, transferring the second pattern to the pattern receiving layer; the first and second patterns being configured to form an assembled pattern.