Back-Side Illuminated Image Sensor Opaque Walls
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Solution Overview
Problem
Back-side illuminated image sensors face issues with light reaching memory areas between charge transfer and read times, degrading image quality due to incomplete optical isolation structures, such as non-contiguous tungsten walls and shield layers.
Innovation Solution
The implementation of conductive tungsten opaque walls and screens on the rear surface of memory regions in a semiconductor wafer, connected to a bias potential, with specific layering and manufacturing steps to ensure effective light blocking, including a hafnium oxide layer and polysilicon separation, to create efficient optical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If opaque walls and shield layers are provided to protect memory regions from light, then light blocking capability is improved, but manufacturing complexity and implementation difficulties increase due to non-contiguous structures
Solution Approach 1:
The patent combines multiple separate light-blocking elements (opaque walls and shield layers) into a single continuous opaque structure that extends from the front surface through to the back surface of the semiconductor wafer. This merging eliminates the gaps between separate components, providing complete optical isolation while simplifying the structure and reducing manufacturing complexity.
Solution Approach 2:
The continuous opaque structure is segmented into different functional zones: front surface opaque walls that extend vertically, intermediate shield layers, and back surface opaque screens. This segmentation allows each zone to be optimized for its specific function while collectively providing complete light blocking when combined.
2Object-affected harmful factors
If separate opaque walls and shield layers are used for optical isolation, then light blocking is partially achieved, but light still passes through gaps between non-contiguous structures
Solution Approach 1:
The patent merges separate opaque walls and shield layers into a continuous opaque structure that eliminates all gaps and discontinuities. This continuous structure ensures complete optical isolation by providing an unbroken barrier that prevents light from reaching memory regions through any pathways.
Solution Approach 2:
The patent introduces intermediate opaque shield layers positioned between the front surface opaque walls and the back surface opaque screens. These intermediary structures fill the gap between the wall and screen, ensuring complete optical isolation by blocking light that might otherwise pass through the intermediate region.
3Object-affected harmful factors
If conductive opaque walls and screens connected to bias potential are implemented, then optical isolation is improved, but device complexity increases
Solution Approach 1:
The opaque structure serves multiple functions simultaneously: it provides optical isolation by blocking light, acts as a conductive element when connected to bias potential for electrical isolation of memory regions, and functions as a structural component integrating front and back surfaces. This multi-functionality reduces the need for separate components.
Solution Approach 2:
The patent combines the optical isolation function and electrical isolation function into a single integrated conductive opaque structure. By making the opaque walls and screens conductive and connecting them to bias potential, the structure simultaneously blocks light and provides electrical isolation, eliminating the need for separate optical and electrical isolation components.
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
This configuration significantly enhances image quality by preventing light from reaching memory regions, improving the protection of stored charges and maintaining image integrity during read operations.
Implementation Method 1
each memory region being located between two opaque walls which extend into the wafer and are in contact with an opaque screen arranged on the rear surface of the memory region
Data Source
AI summary
A back-side illuminated image sensor includes memory regions formed in a semiconductor wafer. Each memory region is located between two opaque walls which extend into the semiconductor wafer. An opaque screen is arranged at the rear surface of the memory region and in electrical contact with the opaque walls.