Integrated Overlay Mark for Multi-Exposure Alignment
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Solution Overview
Problem
Conventional methods require multiple overlay marks and significant area for checking local alignment between lower and upper layers in integrated circuits, especially as linewidths decrease, leading to inefficiencies in overlay accuracy and increased complexity.
Innovation Solution
An overlay mark system that uses N sets of parallel linear patterns and photoresist bars defined by N exposure steps, allowing for the reduction of overlay marks and area required by calculating central coordinates and differences to derive alignment errors and compensate for overlay errors in subsequent exposure steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple overlay marks are used to check local alignment between lower and upper layers, then overlay accuracy is improved, but the area occupied on the wafer and process complexity increase
Solution Approach 1:
The patent combines multiple overlay mark functions into a single integrated structure. The overlay mark includes multiple pattern sets (first and second pattern sets) that can simultaneously check alignment between different layer combinations. By merging what would traditionally require separate overlay marks into one unified structure, the patent reduces the total number of overlay marks needed while maintaining comprehensive alignment verification capability.
Solution Approach 2:
The overlay mark structure is designed to perform multiple alignment checking functions simultaneously. It can verify alignment between the upper layer and different lower layer portions defined by different exposure steps, making a single overlay mark universal for multiple measurement purposes. This multi-functionality eliminates the need for separate specialized overlay marks for each layer combination.
2Measurement precision
If multiple overlay marks are used to check local alignment between lower and upper layers, then overlay accuracy is improved, but device complexity increases
Solution Approach 1:
The overlay mark is segmented into distinct pattern sets (first pattern set and second pattern set), where each set serves a specific alignment verification purpose. This segmentation allows for systematic and organized measurement of different alignment aspects without creating a monolithic complex structure. Each segment can be independently analyzed while contributing to the overall alignment assessment.
3Measurement precision
If conventional overlay marks are used for multi-exposure lower layers, then alignment can be checked, but the number of overlay marks required increases to 1/N efficiency
Solution Approach 1:
The patent merges multiple alignment checking capabilities into a single overlay mark structure that can handle N exposure steps. By combining what would traditionally require N separate overlay marks into one integrated structure, the patent achieves the 1/N efficiency improvement mentioned in the background, reducing the total number of overlay marks needed while maintaining comprehensive alignment verification across all exposure steps.
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 the number and area of overlay marks needed by 1/N, enabling accurate local alignment checking and compensation between upper and lower layers defined by multiple exposure steps, thereby improving overlay accuracy and simplifying the process.
Implementation Method 1
The y-directional linear patterns 114 are scanned by a light beam in the direction 130 to obtain a reflectivity curve 140
Data Source
AI summary
An overlay mark is described, including N sets of parallel x-directional linear patterns respectively defined by N (≧2) exposure steps and N sets of parallel y-directional linear patterns respectively defined by the N exposure steps, and a set of parallel x-directional photoresist bars and a set of parallel y-directional photoresist bars both formed in a lithography process. The N sets of x-directional linear patterns and the set of x-directional photoresist bars are arranged in parallel. The N sets of y-directional linear patterns and the set of y-directional photoresist bars are arranged in parallel.