Backside Illuminated Image Sensor Recess Bonding Pad
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Solution Overview
Problem
The manufacturing process of backside illuminated image sensors faces challenges such as stripe defects in the color filter layer due to the presence of bonding pads, which affect the sensitivity and crosstalk of the sensor, and the protective layer increases the distance between pixel regions and the micro lens array, deteriorating performance.
Innovation Solution
The proposed solution involves forming a recess in the substrate with a second bonding pad electrically connected to the bonding pad through openings in the anti-reflective layer and insulating layer, and a light-blocking pattern with openings corresponding to pixel regions, where the second bonding pad and third bonding pad have a combined thickness less than the recess depth, preventing protrusion and minimizing defects during photoresist coating and etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer is formed on the backside surface of the substrate to protect the substrate and electrically isolate it from the bonding pads, then the substrate is protected and electrical isolation is achieved, but the distance between the pixel regions and the micro lens array is increased, deteriorating the sensitivity and crosstalk of the backside illuminated image sensor
Solution Approach 1:
The patent removes the protective layer from the backside surface of the substrate, extracting the harmful element that caused the contradiction. By eliminating this layer, the distance between pixel regions and micro lens array is reduced, improving sensitivity and crosstalk performance while maintaining substrate protection through alternative means (bonding pads and light-blocking pattern configuration)
Solution Approach 2:
Instead of placing a protective layer on the backside surface as conventionally done, the patent inverts the approach by forming bonding pads and light-blocking patterns directly on the backside surface without an additional protective layer. This reversal eliminates the harmful distance increase while achieving both protection and electrical isolation functions
2Reliability
If the second bonding pad and third bonding pad are formed with sufficient thickness to ensure electrical connection and structural integrity, then reliable electrical connection is achieved, but the combined thickness may exceed the recess depth, causing protrusion and stripe defects during photoresist coating and etching processes
Solution Approach 1:
The patent optimizes the thickness parameters of the second and third bonding pads, setting their combined thickness to be less than the recess depth. This parameter adjustment ensures that the bonding pads remain within the recessed area, preventing protrusion and stripe defects during manufacturing while maintaining sufficient thickness for reliable electrical connection
Solution Approach 2:
The patent uses a thickness that is sufficient for electrical connection but deliberately keeps it below the maximum possible thickness (recess depth). This partial action approach prevents excessive protrusion that would cause defects, while still achieving the necessary electrical connectivity function
3Reliability
If the photoresist pattern thickness is reduced to prevent removal of the third bonding pad during anisotropic etching, then the third bonding pad is preserved, but the photoresist pattern may not provide sufficient protection during the etching process
Solution Approach 1:
The patent introduces the recess structure as an intermediary element between the bonding pads and the etching process. The recessed configuration provides physical protection to the third bonding pad during anisotropic etching, eliminating the need for thick photoresist patterns and their associated stripe defects
Data Source
AI summary
A backside illuminated image sensor includes a substrate having a frontside surface, a backside surface and a recess formed in a backside surface portion thereof, pixel regions disposed in the substrate, an insulating layer disposed on the frontside surface of the substrate, a bonding pad disposed on a frontside surface of the insulating layer, and a second bonding pad disposed in the recess and electrically connected with the bonding pad.