Backside Illumination Sensor Alignment Mark Structure
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Solution Overview
Problem
Existing alignment mark technologies for integrated circuits face challenges in detection due to opaque materials covering backside alignment marks, requiring extensive preparation and risking damage to the smooth front side of substrates during processing.
Innovation Solution
The method involves forming recesses in a silicon substrate, filling them with conductive material, and thinning the substrate to expose alignment marks, which can protrude from the backside surface for enhanced optical detection, allowing for accurate alignment without damaging the front side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If backside alignment marks are used, then detection is possible without covering marks with opaque materials, but extensive preparation steps are required before circuit processing can begin
Solution Approach 1:
The alignment mark structure is prepared in advance by forming recesses in the substrate before any circuit processing begins. The recesses are filled with material that provides optical contrast, enabling immediate alignment mark detection without requiring subsequent covering or removal steps. This preliminary structuring eliminates the need for extensive preparation steps while maintaining detection capability.
2Measurement precision
If extensive preparation steps are performed to create backside alignment marks, then alignment mark detection is enabled, but the risk of damaging the smooth front side of the substrate increases
Solution Approach 1:
The substrate is functionally segmented into distinct regions: the front side maintains its smooth, undamaged state for circuit formation, while the backside contains the alignment mark structures formed in recesses. This spatial separation allows alignment mark preparation and detection without exposing the front side to damaging processing steps such as etching, deposition, or photoresist application.
3Measurement precision
If alignment marks are formed outside the active circuit area, then they can be used for alignment, but they may become covered with opaque materials during later processing steps
Solution Approach 1:
Instead of placing alignment marks on the front side where they would be covered by opaque materials during processing, the alignment marks are inverted to the backside of the substrate. The backside alignment marks are formed in recesses that extend through the substrate thickness, allowing optical detection from the backside without interference from front-side processing materials.
Data Source
AI summary
Provided is an apparatus that includes an integrated circuit located in a first region of a substrate having first and second opposing major surfaces and an alignment mark located in a second region of the substrate and extending through the substrate between the first and second surfaces.