Isolated Wire Bond in Back-Illuminated Image Sensors
Find Innovative SolutionsGenerate Solutions
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 enhanced 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 reduced making wire affixation difficult
Solution Approach 1:
An intermediary structure (isolation region with opposite conductivity type) is introduced between the wire and the semiconductor layer. This intermediary provides electrical isolation through reverse-biased diode action while maintaining a wide opening for wire affixation, avoiding the need for conformal insulating material that would narrow the opening.
Solution Approach 2:
The conductivity type parameter of the semiconductor layer is changed in the isolation region to create a reverse-biased diode. By doping the isolation region with opposite conductivity type, electrical isolation is achieved through parameter change rather than through geometric constriction or insulating materials.
2Reliability
If deep trench isolation regions are formed to prevent electrical shorts, then electrical isolation is achieved, but the fabrication process becomes complex and costly
Solution Approach 1:
Instead of forming deep trench isolation regions that require complex multi-step fabrication processes, the invention applies local quality change by doping only a specific region around the opening with opposite conductivity type. This localized doping creates the necessary electrical isolation without requiring deep trenches or complex fabrication sequences.
Solution Approach 2:
The invention uses parameter change (conductivity type) in the isolation region to achieve electrical isolation. By changing the doping type in a localized region, the patent simplifies the fabrication process compared to deep trench isolation, which requires multiple etching, filling, and planarization steps.
3Reliability
If the wire contacts the semiconductor layer during affixation, then electrical connection is established, but an electrical short occurs rendering the sensor unusable
Solution Approach 1:
An intermediary isolation region with opposite conductivity type is placed between the wire and the semiconductor layer. This intermediary allows the wire to contact the structure for electrical connection to the bond pad while the reverse-biased diode in the isolation region prevents electrical short to the semiconductor layer.
Solution Approach 2:
The potential harmful contact between the wire and semiconductor layer is converted into a beneficial reverse-biased diode configuration. By doping the isolation region with opposite conductivity type, what could be a short circuit becomes a reverse-biased junction that blocks current flow, converting the harmful effect into a protective mechanism.
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 effectively isolates the wire from the semiconductor layer, reducing electrical shorts, simplifying the fabrication process, and lowering production costs while maintaining performance.
Implementation Method 1
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
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.