Optical Lithography Alignment Using Inherent Surface Grain Patterns
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Solution Overview
Problem
Existing alignment methods for lithography on printed circuit boards face accuracy issues due to the need for special alignment marks, which can be undesirable and limited by the size of these marks, especially when trying to avoid holes in the substrate.
Innovation Solution
The method utilizes the unique inherent microscopic characteristics of the work piece surface, such as grain structure, for alignment by capturing and matching images from widely spaced sites on the work piece using cameras on a movable stage and a lithography unit, allowing for precise computation of relative positions without the need for special marks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If special alignment marks are created on the substrate, then alignment reference is established, but the substrate is damaged with holes and the alignment accuracy is limited by mark size
Solution Approach 1:
The patent extracts the alignment reference function from traditional macroscopic marks and relocates it to microscopic surface characteristics naturally present on the substrate. By using inherent surface features at the micrometer scale instead of人工 created marks, the system eliminates substrate damage while achieving higher alignment precision through microscopic imaging and pattern matching algorithms
Solution Approach 2:
The substrate serves its own alignment function through its natural surface characteristics rather than requiring external alignment marks. The inherent microscopic features of the substrate material (grain structure, surface texture) are utilized as self-generated alignment references, eliminating the need for separate marking processes that would damage the substrate
2Measurement precision
If special alignment marks are formed on the substrate, then position reference is established, but the alignment accuracy is limited by the size of these marks
Solution Approach 1:
The patent transitions from two-dimensional macroscopic alignment marks to three-dimensional microscopic surface characteristics. By utilizing the vertical dimension of surface topology and microscopic grain structure, the system achieves sub-micrometer alignment accuracy that transcends the size limitations of traditional planar alignment marks
Solution Approach 2:
The patent changes the scale parameter from macroscopic (visible to naked eye) to microscopic (requiring magnification). This parameter transformation enables alignment precision at the micrometer and sub-micrometer level by utilizing surface features that are inherently present at smaller scales, thereby overcoming the accuracy limitations imposed by larger traditional alignment marks
3Stability of the object's composition
If alignment marks are avoided, then substrate integrity is maintained, but traditional alignment methods cannot achieve sufficient precision
Solution Approach 1:
The patent replaces the mechanical/optical alignment mark system with a computational image processing system. By substituting physical alignment marks with digital pattern matching of microscopic surface features, the system maintains substrate integrity while achieving high precision through algorithmic correlation and coordinate transformation
Data Source
AI summary
An alignment system for optical lithography uses cameras fixed to a movable stage and to a lithography unit to view unique microscopic non-uniformities that are inherent to the surface of a work piece, e.g., metal or ceramic microcrystalline grains, for position referencing. Stage cameras image two sites on the work piece through windows in the stage to establish original position templates. After the work piece has been repositioned, e.g., reversed topside-down, the same two sites are again viewed and template matching establishes the transformed coordinates of the work piece, e.g. by a lithography unit camera under which the stage moves to approximate site locations. Two corner cameras can serve as a coarse positioning mechanism. The alignment system is particular useful for backside alignment in printed circuit board lithography.