Image Sensor Pad Structure FEOL Formation
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Solution Overview
Problem
The challenge in fabricating back side illuminated (BSI) image sensor devices lies in achieving across-wafer and planarization uniformity during the buried color filter array (BCFA) process, where defects often occur due to difficulties in planarizing dielectric materials and forming pad structures, especially near the wafer's edge.
Innovation Solution
Forming pad structures during the front-end-of-line (FEOL) process eliminates the need for a dielectric fill prior to planarization, allowing for a uniform wafer surface and reducing the number of masks required, thereby improving the uniformity and reducing defects by embedding pad structures within the semiconductor substrate before subsequent processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If dielectric fill is performed prior to planarization to form pad structures, then pad structures can be formed in peripheral regions, but planarization uniformity deteriorates and defects increase especially near wafer edges
Solution Approach 1:
The pad structure is formed during the front-end-of-line (FEOL) process before the buried color filter array (BCFA) process and planarization steps. By performing the pad structure formation in advance, the subsequent planarization process operates on a more uniform surface without the complications of filling dielectric material into peripheral openings, thereby eliminating planarization non-uniformity and defects near wafer edges
2Ease of manufacture
If dielectric fill process is used to form pad structures, then pad structures can be created, but the number of process steps and masks increases
Solution Approach 1:
The pad structure formation is merged with the front-end-of-line (FEOL) process steps. The peripheral openings are formed and pad structures are created using the same process sequence as the pixel region, combining multiple functions into a unified process flow that eliminates the need for separate dielectric fill operations and reduces the total number of masks required
Data Source
AI summary
The present disclosure relates to an image sensor with a pad structure formed during a front-end-of-line process. The pad structure can be formed prior to formation of back side deep trench isolation structures and metal grid structures. An opening is formed on a back side of the image sensor device to expose the embedded pad structure and to form electrical connections.