Image Sensor Alignment Marks for Overlay Shift Reduction
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Solution Overview
Problem
The existing image sensor fabrication methods face challenges in achieving precise alignment between processing layers, leading to overlay shifts and misalignment issues, particularly in small pixel designs, which affect the performance and accuracy of image sensors.
Innovation Solution
The proposed solution involves forming multiple sets of alignment marks on the wafer, with each set used as a reference for specific mask layers, reducing the number of alignment transfers and thereby minimizing overlay shifts, ensuring accurate placement of pixel circuit components such as photodiodes and isolation structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple alignment transfers are performed during fabrication, then more mask layers can be processed, but overlay shifts accumulate and alignment precision deteriorates
Solution Approach 1:
The patent divides the alignment reference system into multiple independent sets of alignment marks (first set, second set, third set) corresponding to different mask layers. Each mask layer uses its dedicated alignment marks as reference, eliminating the need for sequential alignment transfers between marks. This segmentation of the alignment reference system allows processing multiple mask layers while maintaining consistent alignment precision for each layer.
2Manufacturing precision
If the number of alignment marks is increased to reduce transfers, then alignment accuracy improves, but device complexity increases
Solution Approach 1:
Each set of alignment marks serves multiple functions: they act as alignment references for their specific mask layer, and simultaneously serve as structural references for subsequent processing steps. The alignment marks are integrated into the fabrication process flow rather than being separate added elements, allowing the same mark structures to fulfill both alignment and process coordination functions.
Data Source
AI summary
The present disclosure provides an alignment method for image sensor fabrication that involve forming a number of set of alignment marks using key process mask layers to improve alignment registration between process mask layers so as to reduce number of alignment transfer improves alignment accuracy between pixel elements. The present disclosure further provides a semiconductor device that includes such alignment mark structures.