BSI Chip Backside Alignment Marks for Thick-Substrate Feature Placement
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Solution Overview
Problem
Backside Illumination (BSI) image sensor chip manufacturing faces alignment challenges due to the increased thickness of the semiconductor substrate after backside grinding, which hinders the alignment of backside features to front-side alignment marks, affecting light-receiving efficiency and image quality.
Innovation Solution
Formation of backside alignment marks that align with front-side alignment marks during the manufacturing process, allowing for precise alignment and improved light absorption through the use of backside high-absorption regions and deep trench isolation structures, along with additional alignment marks to facilitate accurate feature placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the semiconductor substrate thickness is increased after backside grinding, then light absorption efficiency is improved, but alignment precision between backside features and front-side alignment marks deteriorates
Solution Approach 1:
The patent introduces an intermediary alignment mark structure that penetrates through the thickened substrate from the backside to the frontside. This intermediary structure serves as a mediator that bridges the alignment gap between backside features and front-side alignment marks, enabling precise alignment even when the substrate thickness is increased for improved light absorption efficiency
Solution Approach 2:
The patent transitions from two-dimensional alignment (on the surface) to three-dimensional alignment by creating alignment marks that extend through the substrate thickness. This dimensional change allows alignment information to be transmitted across the entire thickness of the substrate, solving the alignment precision problem while maintaining the thickened substrate structure for better light absorption
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
Enhances light-receiving efficiency and image quality by ensuring accurate alignment and efficient light absorption, even with thicker substrates, thereby improving the overall performance of BSI image sensor chips.
Implementation Method 1
the second alignment mark is formed by etching the semiconductor substrate to form trenches extending from the backside of the semiconductor substrate into the semiconductor substrate, wherein the second alignment mark aligns with the first alignment mark
Implementation Method 2
each image sensor element including a photodiode and other elements, to absorb light and convert the sensed light into digital data or electrical signals
Data Source
AI summary
A method includes forming image sensors in a semiconductor substrate. A first alignment mark is formed close to a front side of the semiconductor substrate. The method further includes performing a backside polishing process to thin the semiconductor substrate, forming a second alignment mark on the backside of the semiconductor substrate, and forming a feature on the backside of the semiconductor substrate. The feature is formed using the second alignment mark for alignment.