Edge-Dominant Alignment Method for Exposure Scanner Overlay Accuracy
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Solution Overview
Problem
The increasing complexity of semiconductor devices due to shrinking feature sizes poses challenges for achieving accurate wafer alignment and overlay accuracy in exposure processes, as existing metrology techniques have limitations in measurement uncertainties, making it difficult to maintain the process window for next-generation devices.
Innovation Solution
An edge-dominant alignment method is introduced in the exposure scanner system, where alignment marks are strategically distributed along the outer edges of the wafer, allowing for a focused alignment process on specific zones to enhance overlay accuracy, utilizing a controller to determine scan paths and perform real-time feedback for precise alignment adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical overlay metrology is used for alignment measurement, then overlay accuracy between patterned layers can be measured, but measurement uncertainties are too large for next-generation devices
Solution Approach 1:
The patent segments the alignment measurement process into two distinct stages: a coarse alignment stage using optical overlay metrology to achieve initial positioning, and a fine alignment stage using electron beam-induced charge (EBIC) signals to achieve sub-nanometer precision. This segmentation allows each stage to optimize for its specific function, resolving the contradiction between measurement capability and required precision.
Solution Approach 2:
The patent introduces an intermediary mechanism - alignment marks with specific geometric features (such as L-shaped or T-shaped marks) that serve as reference targets for both optical and electron beam measurements. These intermediary marks enable the transition from optical to electron beam alignment and facilitate the combination of measurements from both systems to achieve ultra-high precision.
2Manufacturing precision
If alignment marks are distributed uniformly across the wafer, then comprehensive coverage is achieved, but the number of alignment operations increases time and cost
Solution Approach 1:
The patent applies local quality by strategically placing alignment marks at specific locations on the wafer (such as at the corners or along the periphery) rather than uniformly distributing them across the entire surface. This localized placement optimizes alignment accuracy for the specific exposure field being used while minimizing the total number of alignment operations required.
Solution Approach 2:
The patent implements partial action by performing alignment operations only on the necessary portions of the wafer or exposure field rather than the entire wafer surface. By identifying and aligning only the critical shot areas or fields required for the current exposure task, the system achieves sufficient alignment accuracy without the time and cost penalty of comprehensive full-wafer alignment.
3Manufacturing precision
If more alignment marks are used to improve accuracy, then overlay precision increases, but the complexity and cost of the alignment process increases
Solution Approach 1:
The patent extracts and utilizes specific geometric features from alignment marks (such as corner vertices or intersection points of L-shaped/T-shaped marks) as the primary reference targets for alignment. By focusing measurement and alignment operations on these extracted critical features rather than the entire mark structure, the system achieves high precision with minimal complexity.
Solution Approach 2:
The patent changes the measurement parameters by switching from optical measurement parameters to electron beam measurement parameters. The electron beam system operates at different energy levels and detection thresholds to generate EBIC signals, allowing precise measurement of alignment mark positions with sub-nanometer resolution. This parameter change enables high accuracy without requiring a proportional increase in the number of alignment marks.
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 improves alignment accuracy and reduces alignment residuals by prioritizing edge shot areas with alignment marks, effectively increasing the process window for semiconductor devices, even in larger wafers, while minimizing time and cost by optimizing the number of aligned areas.
Implementation Method 1
a first EBIC signal is generated from a first alignment mark by irradiating the first alignment mark with a first electron beam
Data Source
AI summary
An edge-dominant alignment method for use in an exposure scanner system is provided. The method includes the steps of: providing a wafer having a plurality of shot areas, wherein each shot area has a plurality of alignment marks; determining a first outer zone of the wafer, wherein the first outer zone includes a first portion of the shot areas along a first outer edge of the wafer; determining a scan path according to the shot areas of the first outer zone; and performing an aligning process to each shot area of the first outer zone according to the scan path and an alignment mark of each shot area of the first outer zone.