Overlay Mark with Segmented Trenches for Dual-Axis Alignment
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Solution Overview
Problem
Existing overlay marks for IC processes cannot check y-directional alignment accuracy between the lithography process and the first device area and x-directional alignment accuracy between the lithography process and the second device area, limiting their effectiveness in ensuring complete alignment accuracy.
Innovation Solution
The proposed overlay mark includes two x-directional and two y-directional photoresist bars formed over a lower layer with corresponding trenches, ensuring that the central lines of the trenches and photoresist bars coincide when the lower layer is fully aligned with the lithography process, allowing for the measurement of both x-directional and y-directional alignment accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If only two y-directional and two x-directional trenches are formed in the lower layer, then the alignment accuracy in one direction can be checked, but the alignment accuracy in the other direction cannot be checked
Solution Approach 1:
The overlay mark is segmented into four distinct components: two y-directional photoresist bars, two x-directional photoresist bars, two first x-directional trenches, two first y-directional trenches, two second x-directional trenches, and two second y-directional trenches. This segmentation allows independent measurement of alignment accuracy in both x and y directions, resolving the limitation of checking only one direction at a time
Solution Approach 2:
The invention extends the overlay mark structure from a single-direction checking capability to multi-directional checking by adding photoresist bars and trenches in both x and y directions. This dimensional expansion enables simultaneous verification of alignment accuracy across multiple axes, transforming a unidirectional measurement system into a multidirectional one
2Ease of manufacture
If the overlay mark structure is simplified to reduce fabrication complexity, then manufacturing becomes easier, but the ability to check alignment accuracy in multiple directions is lost
Solution Approach 1:
The overlay mark structure is designed with multi-functionality, where the same set of photoresist bars and trenches serve dual purposes: they define the overlay mark position and simultaneously provide reference features for measuring alignment accuracy in both x and y directions. This universal design eliminates the need for separate marking and measurement features
Solution Approach 2:
The invention merges the functions of alignment marking and alignment verification into a single integrated structure. The photoresist bars and trenches are positioned such that they both define the overlay mark boundaries and create measurable reference points for alignment checking in multiple directions, combining what would traditionally be separate features
Data Source
AI summary
An overlay mark for checking the alignment accuracy between a lower layer and a lithography process for defining an upper layer is described, including a part of the lower layer having two first x-directional trenches, two first y-directional trenches, two second x-directional trenches and two second y-directional trenches therein, and two x-directional and two y-directional photoresist bars thereover that are surrounded by the trenches and formed in the lithography process. When the lower layer is fully aligned with the lithography process, the intersection of the central line of the two first x-directional trenches and that of the two first y-directional trenches, the intersection of the central line of the two second x-directional trenches and that of the two second y-directional trenches and the intersection of the central line of the two x-directional photoresist lines and that of the two y-directional photoresist lines coincide with each other.