BSI Image Sensor Mirror Layer for Photon Efficiency and Crosstalk
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Solution Overview
Problem
Existing backside illumination (BSI) image sensors have low photon detection efficiency and suffer from substantial crosstalk between adjacent photosensitive devices due to light interference and reflection issues caused by the interconnection structure layer.
Innovation Solution
A mirror layer is introduced between the interconnection structure layer and the array substrate to reflect light more efficiently, reducing the distance between the mirror layer and photosensitive devices while maintaining electrical insulation, thereby improving photon detection efficiency and minimizing crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the array substrate is thinned to improve light incident efficiency, then the light incident efficiency is improved, but the substrate becomes too thin and requires attachment to a carrier
Solution Approach 1:
A mirror layer is introduced as an intermediary component between the thinned array substrate and the interconnection structure layer. This mirror layer serves multiple functions: it reflects light to improve photon detection efficiency, provides mechanical support to the thinned substrate, and enables electrical insulation while maintaining a compact structure. The mirror layer acts as a mediator that resolves the contradiction between substrate thinning for light efficiency and the need for structural integrity.
2Illumination intensity
If the mirror layer is placed close to the photosensitive devices to improve photon detection efficiency, then the photon detection efficiency is improved, but electrical insulation may be compromised
Solution Approach 1:
The mirror layer is designed to perform multiple functions simultaneously: optical reflection to improve photon detection efficiency, mechanical support for the thinned substrate, and electrical insulation through integrated dielectric structures. By making the mirror layer multi-functional, the patent resolves the contradiction between placing it close to photosensitive devices for optical performance and maintaining electrical insulation reliability.
Solution Approach 2:
The mirror layer is constructed as a composite structure combining reflective materials (such as metal layers) with dielectric materials for electrical insulation. This composite approach allows the mirror layer to be positioned close to photosensitive devices while maintaining proper electrical insulation through the dielectric components integrated into the composite structure.
3Ease of manufacture
If the interconnection structure layer is disposed directly on the array substrate to simplify manufacturing, then the manufacturing process is simplified, but light interference and crosstalk increase
Solution Approach 1:
The mirror layer serves as an intermediary between the array substrate and the interconnection structure layer, preventing direct contact while maintaining electrical connection through controlled vias. This intermediary position blocks light interference and crosstalk between the interconnection structure and photosensitive devices, while still allowing for a relatively simplified manufacturing process compared to more complex isolation structures.
4Productivity
If hybrid bonding is used to connect upper and lower wafers to reduce inter-chip interconnection area and RC delay, then the interconnection area and RC delay are reduced, but the bonding process complexity increases
Solution Approach 1:
The mirror layer and its integrated dielectric structures are prepared in advance during the array substrate fabrication process, creating pre-formed bonding surfaces with appropriate electrical insulation and reflection properties. This preliminary preparation simplifies the subsequent hybrid bonding process by eliminating the need for additional insulation layer deposition and patterning steps, thus reducing bonding process complexity while maintaining high interconnection efficiency.
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
The mirror layer enhances photon detection efficiency and reduces crosstalk between adjacent photosensitive devices, leading to improved signal-to-noise ratio and performance of the BSI image sensor.
Implementation Method 1
A mirror layer is introduced between the interconnection structure layer and the array substrate to reflect light more efficiently
Data Source
AI summary
A backside illuminated (BSI) image sensor includes: an array substrate containing one or more photosensitive devices and including a first surface; a mirror layer disposed at a side of the first surface of the array substrate and electrically insulted from the one or more photosensitive devices; and an interconnection structure layer disposed at a side of the mirror layer facing away from the array substrate, electrically connected to the one or more photosensitive devices, and electrically insulated from the mirror layer.