Back-illuminated Image Sensor Wire Bonding Isolation
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Solution Overview
Problem
Back-illuminated image sensors face issues with electrical shorts due to wire bonding, which reduces yield and increases costs, as existing isolation techniques either narrow the opening for wire affixation or require complex and costly deep trench isolation processes.
Innovation Solution
A method involving forming a region of opposite conductivity type from the semiconductor layer's backside to its frontside to surround the opening for bond pad exposure, creating a reverse-biased diode that prevents electrical shorts when a wire is affixed, and optionally using a well or additional regions for isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conformal insulating material is deposited to line the sidewalls of the opening, then electrical isolation is achieved, but the opening width is narrowed such that wire affixation becomes impossible
Solution Approach 1:
The patent extracts the isolation function from a conformal coating approach and implements it through a separate isolation structure (isolation ridge or isolation layer) positioned adjacent to the opening. This allows the opening to maintain its full width for wire affixation while the isolation structure provides the necessary electrical isolation between the wire and semiconductor substrate.
2Reliability
If deep trench isolation regions are formed to prevent electrical shorts, then reliability is improved, but the fabrication process becomes complex and costly
Solution Approach 1:
The patent employs a simpler isolation structure (isolation ridge formed from deposited material or a dedicated isolation layer) rather than complex deep trench isolation. This approach achieves the necessary electrical isolation function with fewer fabrication steps, lower complexity, and reduced cost while maintaining reliability.
3Reliability
If deep trench isolation regions are formed to prevent electrical shorts, then reliability is improved, but production costs increase
Solution Approach 1:
The patent uses a cost-effective isolation structure (isolation ridge or isolation layer) that can be formed through standard deposition and etching processes, avoiding the need for complex deep trench isolation fabrication. This reduces production costs while maintaining the essential function of preventing electrical shorts during wire bonding.
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 simplifies the isolation process, reduces production costs, and enhances the reliability and performance of image sensors by preventing electrical shorts during both package and wafer testing.
Implementation Method 1
A first region having a second conductivity type extends from the backside of the semiconductor layer to the frontside of the semiconductor layer and surrounds the opening... creating a reverse-biased diode that prevents electrical shorts when a wire is affixed
Data Source
AI summary
An electrical component includes a semiconductor layer having a first conductivity type and a interconnect layer disposed adjacent to a frontside of the semiconductor layer. At least one bond pad is disposed in the interconnect layer and formed adjacent to the frontside of the semiconductor layer. An opening formed from the backside of the semiconductor layer and through the semiconductor layer exposes at least a portion of the bond pad. A first region having a second conductivity type extends from the backside of the semiconductor layer to the frontside of the semiconductor layer and surrounds the opening. The first region can abut a perimeter of the opening or alternatively, a second region having the first conductivity type can be disposed between the first region and a perimeter of the opening.