Backside Illuminated Image Sensor Substrate Thinning and Packaging
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Solution Overview
Problem
Conventional back side illumination (BSI) image sensors face challenges in achieving high quantum efficiency due to thick substrates, which require costly and time-consuming polishing processes, and result in wasted die area from special shell package types and bond wires, limiting fill factor and increasing production costs.
Innovation Solution
A method involving a substrate with a formed pixel region, interlayer insulating layer, and metal lines, along with an isolation carrier layer having a hole array, where conductors are placed to form bumps, allowing for reduced substrate thickness and eliminating the need for bond wires, thereby enhancing quantum efficiency and simplifying packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thick substrate is used in BSI image sensor, then structural strength is improved, but quantum efficiency deteriorates due to light absorption
Solution Approach 1:
The substrate is segmented into multiple thin layers including a first substrate layer, a second substrate layer, and an intermediate layer. This segmentation allows each layer to be optimized independently - the overall structure maintains strength while individual thin layers enable better light transmission for high quantum efficiency.
Solution Approach 2:
The patent uses composite substrate structure with different material layers (first substrate layer, second substrate layer, intermediate layer) that have different optical and mechanical properties. This composite structure achieves both mechanical strength and optical transparency for high quantum efficiency.
2Reliability
If substrate thickness is reduced to improve quantum efficiency, then manufacturing complexity increases due to polishing process requirements
Solution Approach 1:
The substrate is pre-divided into multiple thin layers before the main fabrication process. This preliminary action eliminates the need for complex post-fabrication thinning and polishing processes, as the thin substrate structure is already in place before device formation.
Solution Approach 2:
Instead of starting with a thick substrate and thinning it down through complex polishing processes, the patent inverts the approach by starting with thin substrate layers and building up the device structure on top, thereby eliminating the need for complex thinning operations.
3Strength
If bond wires and special shell package types are used for thin substrate packaging, then structural support is improved, but die area is wasted
Solution Approach 1:
The patent extracts and eliminates the need for bond wires and special shell package types by using a carrier substrate that provides both mechanical support and electrical connection functions. This removal of unnecessary components maximizes the usable die area.
Solution Approach 2:
The carrier substrate serves multiple functions simultaneously: it provides mechanical support for the thin substrate, establishes electrical connections to the pixel circuits, and enables packaging without requiring additional bond wires or special shell structures. This multi-functionality eliminates wasted die area.
4Reliability
If conventional polishing process is used to thin substrate, then quantum efficiency is improved, but production cost and time increase
Solution Approach 1:
The substrate is pre-divided into thin layers before device fabrication, eliminating the need for time-consuming polishing operations during or after device formation. This preliminary thinning action significantly improves production efficiency while achieving the same quantum efficiency benefits.
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 approach enhances quantum efficiency by optimizing light penetration and reduces production costs by eliminating the need for expensive polishing and bond wires, while improving packaging efficiency.
Implementation Method 1
grinding a lower surface of the substrate to reduce the thickness of the substrate
Data Source
AI summary
The present invention provides an image sensor and a fabricating method thereof capable of approaching higher quantum efficiency and reducing cost. The method comprises: providing a substrate; forming a pixel region on a top surface of the substrate; forming an interlayer insulating layer and at least a metal line on the pixel region; forming an isolation carrier layer having a hole array therein on the interlayer insulating layer; grinding a lower surface of the substrate to reduce the thickness of the substrate; placing a plurality of conductors into the hole array to form a plurality of bumps on the isolation carrier layer.