Wafer Alignment Marks for Laser Separation
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Solution Overview
Problem
Separating integrated circuits on a wafer using the bottom surface is challenging due to the milky appearance of epitaxial wafer substrates, which makes it difficult to distinguish saw lines from the integrated circuits, especially when they are narrow or virtually zero, leading to misalignment during the separation process.
Innovation Solution
Incorporating alignment marks formed from metallization layers on the wafer substrate, which reflect light and can be detected from the bottom surface, allowing for accurate alignment and separation of integrated circuits using a separating device like a laser.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the bottom surface of the wafer is used for separating integrated circuits, then the separation process can be performed without disturbing the top surface structure, but the milky appearance of epitaxial wafer substrates makes it difficult to detect saw lines and alignment marks
Solution Approach 1:
The patent applies contrast enhancement by making alignment marks highly reflective (bright) against the milky (diffuse) background of the epitaxial wafer substrate. The alignment marks are designed to reflect light strongly, creating visual contrast that enables reliable detection by optical systems despite the inherently low-contrast milky appearance of the substrate.
Solution Approach 2:
The patent introduces alignment marks as intermediary elements that facilitate the detection process. These marks serve as mediators between the optical detection system and the saw lines, providing reliable reference points that can be detected through the milky substrate to enable accurate alignment and separation.
2Manufacturing precision
If narrow or virtually zero-width saw lines are used to separate integrated circuits, then the separation precision is improved, but the saw lines become difficult to distinguish from the integrated circuits when viewed from the bottom surface
Solution Approach 1:
The patent segments the visual field into distinct elements: highly reflective alignment marks, diffuse milky substrate, and narrow saw lines. By making the alignment marks significantly more reflective than the surrounding substrate and circuit structures, the system can detect these segmented elements individually, allowing precise localization of narrow saw lines that would otherwise be indistinguishable.
Solution Approach 2:
The patent creates optical contrast differences (analogous to color changes) by designing alignment marks with high reflectivity while the substrate and circuit structures have low reflectivity. This contrast mechanism enables the detection system to distinguish narrow saw lines from the integrated circuits by referencing the highly visible alignment marks.
3Difficulty of detecting and measuring
If alignment marks are formed from metallization layers, then the reflectivity and detectability from the bottom surface is improved, but the manufacturing process complexity increases
Solution Approach 1:
The patent merges the function of alignment marks with the existing metallization layers used in integrated circuit fabrication. By forming alignment marks from the same metallization materials and processes already employed for circuit interconnections, the patent achieves high reflectivity for bottom-surface detection without adding separate manufacturing steps or materials.
Solution Approach 2:
The metallization layers serve multiple functions: they provide both the electrical interconnections for the integrated circuits and the highly reflective alignment marks for separation processes. This multi-functionality eliminates the need for separate alignment mark structures, reducing overall device complexity while maintaining high detectability.
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
The alignment marks improve the detection and alignment of saw lines from the bottom surface, enabling reliable separation of integrated circuits, even on epitaxial wafers with a milky appearance, by enhancing the contrast and reflectivity of the alignment marks.
Implementation Method 1
the alignment marks being formed from at least one of the superposed layers... the alignment marks improve the detection and alignment of saw lines from the bottom surface, enabling reliable separation of integrated circuits, even on epitaxial wafers with a milky appearance, by enhancing the contrast and reflectivity of the alignment marks
Data Source
AI summary
Integrated circuits (1) on a wafer comprise a wafer substrate (2) and a structure applied on a surface (4) of the wafer substrate (2). The structure forms a plurality of integrated circuits (1) formed on the wafer substrate (2) and the integrated circuits (1) are separated by saw lines (6, 7). The structure comprises a plurality of superposed layers (9a-9e) formed on the wafer substrate (2) and a top layer (10) formed on the superposed layers (9a-9e). The integrated circuit (1) on the wafer further comprise a plurality of alignment marks (3) intended for aligning a separating device (18) for separating the integrated circuits (1) on the wafer into individual integrated circuits (1) during a separation process, wherein the alignment marks (3) are formed from at least one of the superposed layers (9a-9e).