Alignment Mark Positioning Under Opaque Layers
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Solution Overview
Problem
In lithographic processes, alignment marks on substrates become obscured or distorted by new material layers, making it difficult to accurately position device patterns, requiring additional costly processing steps and space for additional marks.
Innovation Solution
A method and apparatus that use relative position information of edge portions of the substrate, measured by an angle-selective camera, to derive the position of obscured alignment marks, allowing for accurate positioning without additional patterning steps, and optionally removing the overlying structure to reveal the marks for more precise measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional alignment marks are formed in subsequent layers to compensate for obscured original marks, then measurement reliability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies preliminary action by measuring and recording the positions of substrate edge portions before the opaque layer is deposited. This early measurement captures reference data that can be used later to calculate mark positions even after the marks become obscured, eliminating the need for additional marks or process steps.
Solution Approach 2:
The patent uses optical copying by capturing images of the substrate edge portions with a camera system. These optical copies of edge positions are stored and later used to derive mark positions through calculation, replacing the need for physical access to the original marks beneath the opaque layer.
2Measurement precision
If windows are cut in opaque layers to reveal underlying alignment marks, then measurement precision is improved, but manufacturing complexity and time increase
Solution Approach 1:
The patent performs the measurement action beforehand by capturing edge portion positions before the opaque layer is deposited. This preliminary measurement eliminates the need for subsequent window-cutting operations to access the marks, saving processing time while maintaining measurement precision.
Solution Approach 2:
The patent introduces substrate edge portions as intermediary reference objects. Instead of directly measuring the obscured alignment marks, the system measures the edge portions which serve as accessible intermediaries, and then calculates the mark positions based on the known relative relationships between edges and marks.
3Manufacturing precision
If the substrate edge position is measured before and after opaque layer deposition, then mark position accuracy is maintained, but measurement complexity increases
Solution Approach 1:
The patent applies universality by using the same camera system for multiple purposes: measuring substrate edge positions, capturing mark positions when visible, and potentially measuring other features. This multi-functional approach maintains measurement accuracy without requiring separate specialized measurement systems.
Solution Approach 2:
The patent implements feedback by using the measured edge portion positions to calculate and verify mark positions. The system continuously references the edge measurements to maintain accurate mark positioning information throughout the manufacturing process, even as layers are added.
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
Enables accurate determination and positioning of alignment marks under opaque layers without additional processing or space, reducing costs and complexity, and allowing for precise control of pattern placement in lithographic processes.
Implementation Method 1
an optical system of the camera is angle-selective such that a portion of said edge region having a specific bevel angle is accentuated in said images
Data Source
AI summary
A target structure such as an alignment mark on a semiconductor substrate becomes obscured by an opaque layer so that it cannot be located by an alignment sensor. A position for the mark is determined using an edge position sensor and relative position information that defines the position of the mark relative to one or more edge portions of the substrate is stored prior to formation of the opaque layer. A window can be opened in the opaque layer, based on the determined position. After revealing the target structure, the alignment sensor can, if desired, measure more accurately the position of the target structure, for use in controlling a further lithographic step. The edge position sensor may be a camera having an angle-selective behavior. The edge position sensor may be integrated within the alignment sensor hardware.