Infrared Interferometric Wafer Alignment Angstrom Precision
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Solution Overview
Problem
Conventional infrared alignment techniques are limited by resolution, typically achieving only 500 nm or more due to the use of conventional alignment marks and imaging methods, which are insufficient for many applications requiring angstrom-level precision.
Innovation Solution
An interferometric-spatial-phase imaging (ISPI) system with embedded global coordinate reference marks on a substrate wafer, utilizing grating and checkerboard patterns on two surfaces for continuous six-axis control of a scanning probe tip, allowing for angstrom-level alignment and position measurement without external alignment marks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional infrared imaging techniques are used with alignment marks, then the system can achieve alignment capability, but the resolution is limited to 500 nm or more due to diffraction limits at infrared wavelengths
Solution Approach 1:
The patent replaces conventional direct imaging methods with interferometric measurement techniques. Instead of directly imaging alignment marks with infrared optics, the system uses interference patterns formed by splitting and recombining light waves to achieve angstrom-level measurement precision, overcoming the diffraction limit that constrains conventional imaging resolution.
Solution Approach 2:
The patent changes the measurement parameter from direct spatial resolution to interferometric phase measurement. By measuring the phase difference of interfering light waves rather than directly resolving spatial features, the system achieves precision far below the diffraction limit of infrared wavelengths, transforming the fundamental measurement parameter to bypass optical resolution constraints.
2Measurement precision
If signal processing is applied to low-resolution infrared images to improve resolution, then matching precision can be extended to within 100 nm, but this is still insufficient for many applications requiring angstrom-level precision
Solution Approach 1:
The patent replaces post-processing signal enhancement methods with preemptive interferometric measurement. Instead of trying to recover lost spatial information through signal processing of low-resolution images, the system directly measures position with angstrom-level precision using interference patterns, eliminating the information loss problem at its source rather than attempting to recover it afterward.
3Ease of manufacture
If conventional alignment marks are used on the wafer face, then alignment can be performed, but the marks occupy valuable device patterning area and are subject to degradation during processing
Solution Approach 1:
The patent inverts the conventional approach by placing alignment marks on the backside of the wafer rather than on the front device surface. This inversion allows alignment marks to be fabricated once during wafer manufacturing without occupying device patterning area, and they remain stable throughout subsequent processing steps since they are not exposed to the same degradation mechanisms as frontside marks.
Solution Approach 2:
The patent makes the wafer backside alignment marks serve multiple functions: they provide a stable reference framework for all subsequent alignment operations, enable wafer-to-wafer registration, and serve as a permanent coordinate system throughout the fabrication process. This multi-functional alignment mark system eliminates the need for separate alignment marks on each device layer.
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 angstrom-level precision in alignment and position measurement, overcoming resolution limitations of conventional methods and maintaining accuracy throughout wafer processing and device fabrication, with the ability to use broadband light and infrared illumination without affecting detectivity.
Implementation Method 1
interferometric-spatial-phase imaging
Implementation Method 2
grating and checkerboard patterns
Data Source
AI summary
An interferometric-spatial-phase imaging (ISPI) system includes a substrate wafer. An alignment configuration is permanently embedded in the substrate wafer. The alignment configuration uses a global coordinate reference system by providing a plurality of global reference marks that encompass up to the entire substrate wafer. A plurality of alignment markings is provided on a surface in close proximity to the alignment configuration for obtaining continuous six-axis control of a scanning probe tip with respect to the global coordinate reference system.