Overlay Mark for IC Alignment Accuracy
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Solution Overview
Problem
Conventional overlay marks in IC fabrication are ineffective in determining alignment accuracy between two exposure steps, particularly failing to assess alignment in both X and Y directions between the lithography process and patterns defined by the first and second exposure steps, and require increased area for accurate estimation.
Innovation Solution
An overlay mark comprising two sets of bar-like figures formed in the lower wafer layer during each exposure step, with specific dimensions and orientations, allowing for the formation of rectangular frames that are aligned with a photoresist pattern, enabling the determination of positional parameters to assess alignment accuracy in both X and Y directions between the first and second exposure steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional overlay marks with four trenches are used to check alignment accuracy, then alignment in one direction can be determined, but alignment accuracy in both X and Y directions between lithograph process and both exposure steps cannot be completely determined
Solution Approach 1:
The overlay mark is segmented into multiple functional components: first exposure step patterns (first set of trenches), second exposure step patterns (second set of trenches), and lithograph process patterns (photoresist figures). Each set of patterns is specifically designed to check alignment in both X and Y directions with its corresponding process step, enabling comprehensive alignment verification through separate measurement functions.
Solution Approach 2:
The invention extends alignment checking from single-direction measurement to two-dimensional alignment verification by adding Y-directional bar-like figures and corresponding measurement capabilities. This allows simultaneous determination of alignment accuracy in both X and Y directions between the lithograph process and exposure steps, transforming the measurement system from one-dimensional to two-dimensional assessment.
2Adaptability or versatility
If four trenches are defined in the first exposure step and another four trenches are defined in another part of the lower wafer layer during the second exposure step to estimate alignment accuracy in both directions, then complete alignment checking is possible, but the area occupied by the overlay mark increases by two times
Solution Approach 1:
The invention merges the alignment checking functions for both exposure steps and lithograph process into a single integrated overlay mark structure. By combining first exposure patterns, second exposure patterns, and lithograph patterns within one compact mark, the design achieves comprehensive alignment verification (both X and Y directions for all three processes) without requiring separate overlay marks, thereby reducing the total area occupied.
Solution Approach 2:
The overlay mark is designed with multi-functionality to perform multiple alignment checking tasks simultaneously. The same mark structure enables determination of alignment accuracy between lithograph process and first exposure step, between lithograph process and second exposure step, and provides comprehensive two-dimensional alignment verification, eliminating the need for multiple separate measurement marks.
3Area of stationary object
If conventional overlay marks are used, then the area occupied is reduced, but the ability to estimate alignment accuracy between lower wafer layer patterns defined in first and second exposure steps is lost
Solution Approach 1:
The overlay mark is divided into distinct pattern sets: first exposure step patterns (first set of trenches), second exposure step patterns (second set of trenches), and lithograph process patterns. This segmentation allows independent measurement and analysis of alignment accuracy between any combination of these processes, including the critical ability to estimate alignment between lower wafer layer patterns from both exposure steps.
Data Source
AI summary
An overlay mark is described, wherein the overlay mark is used for checking the alignment accuracy between a lower layer defined by two exposure steps and a lithography process for defining an upper layer, including a part of the lower layer and a photoresist patter. The part of the lower layer includes two first x-directional, two first y-directional bar-like patterns. The first x-directional and first y-directional bar-like patterns are defined by one exposure step to define a first rectangle. The second x-directional and second y-directional bar-like patterns are defined by another exposure to define a second rectangle, wherein the second rectangle is wider than the first rectangle. The photoresist pattern, which is formed by the lithograph process, is disposed over the part of the lower layer and is surrounded by the bar-like patterns.