Overlay Structures Using Offset Dummy Features
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Solution Overview
Problem
Accurate overlay of layers in semiconductor structures is challenging due to shifting issues, which can lead to defects, and existing measurement techniques suffer from noise and process variations, making it difficult to determine and correct shifts effectively.
Innovation Solution
Implementing offset dummy features in each layer, using a scanning electron microscope overlay technique to measure distances between these features, and applying in-die self-calibration to determine shifts and correct overlay errors, thereby eliminating measurement noise and process variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical overlay measurement technique is used to measure shift by looking from top layer down through bottom layer, then overlay measurement can be performed, but measurement noise occurs due to discrepancies in measurement technique and process variation
Solution Approach 1:
The patent extracts the measurement function from the main overlay structure by introducing separate dummy features that are dedicated solely to measurement purposes. These dummy features are positioned in specific layers and used exclusively for measuring overlay shifts, separating the measurement function from the functional device features. This extraction allows for specialized measurement structures that are optimized for measurement accuracy without being affected by process variations in the main device features.
Solution Approach 2:
The patent introduces dummy features as intermediary elements between the measurement system and the actual overlay structure. These dummy features serve as mediators that capture overlay shift information in a way that is less susceptible to measurement noise and process variations. By measuring the position of dummy features rather than direct device features, the system obtains more reliable overlay data.
2Volume of moving object
If layers are shrunk to meet device requirements, then device scaling is achieved, but overlay alignment becomes more difficult and shifting issues increase
Solution Approach 1:
The patent segments the overlay measurement function from the main device structure by using separate dummy features in specific layers. This segmentation allows the measurement system to independently track overlay shifts without being constrained by the reduced dimensions of the scaled device features. The dummy features provide a larger, more measurable reference framework that remains effective even as device features shrink.
Solution Approach 2:
The patent implements preliminary action by pre-positioning dummy features in strategic locations within the layer structure before the actual overlay process. These pre-positioned features serve as reference points that capture cumulative overlay shifts across multiple lithography steps. By establishing these measurement references in advance, the system can accurately track and correct overlay errors even as device dimensions are reduced.
Data Source
AI summary
The present disclosure generally relates to semiconductor structures and, more particularly, to overlay structures and methods of manufacture. The method includes locating a first plurality of offset dummy features in a first layer; locating a second plurality of offset dummy features in a second layer; measuring a distance between the first plurality of offset dummy features and the second plurality of offset dummy features; and determining that the first layer or the second layer is shifted with respect to one another based on the measurement.