Backside Illuminated Sensor Seal Ring Support
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Solution Overview
Problem
Backside illuminated imaging sensors are susceptible to mechanical stress during the die sawing process due to their thinness, which compromises their integrity and reliability, and front side illuminated sensors have limited fill factor issues.
Innovation Solution
The implementation of seal ring support structures on the backside of the semiconductor wafer, which are formed in or on the outer regions of the dielectric layers to provide mechanical protection and structural support, reducing the vulnerability to die saw stress and enhancing the sensor's durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the wafer is thinned to improve sensitivity, then light sensitivity is improved, but mechanical strength deteriorates making the sensor more susceptible to die saw stress
Solution Approach 1:
The support structure is segmented into multiple dielectric layers with different materials (first dielectric layer with first material, second dielectric layer with second material) positioned at different locations on the backside. This segmentation allows each layer to provide targeted mechanical support to different regions of the thinned wafer, maintaining overall structural integrity while preserving the thinned state for light sensitivity.
Solution Approach 2:
Different dielectric materials are used at different locations on the backside of the wafer. The first dielectric layer and second dielectric layer have different material properties, providing locally optimized mechanical support. This local quality variation ensures that support is provided where needed most while maintaining the thinned wafer structure for optimal light detection.
2Reliability
If seal rings are formed to protect from contaminants and mechanical stress, then reliability is improved, but the thin wafer becomes more susceptible to damage during manufacturing
Solution Approach 1:
The seal ring support structures are formed on the backside of the wafer before the die sawing process and contaminant exposure. This preliminary action provides mechanical reinforcement in advance, allowing the thin wafer to withstand subsequent manufacturing stresses and contaminant exposure without damage, thereby improving reliability.
Solution Approach 2:
The dielectric layers act as intermediary support structures between the thin active wafer layer and the external mechanical stresses. These intermediary layers provide a cushioning effect, distributing mechanical stress away from the fragile thin wafer regions while still allowing the seal rings to provide contaminant protection.
3Area of stationary object
If the wafer is made extremely thin for backside illumination, then fill factor is improved, but the wafer becomes more vulnerable to mechanical stress during die sawing
Solution Approach 1:
Instead of adding support structures on the front side (same dimension as light entry), the patent places support structures on the backside of the wafer. This dimensional change allows the front side to maintain maximum openness for light collection (high fill factor) while the backside provides mechanical reinforcement, resolving the contradiction between fill factor and manufacturing integrity.
Data Source
AI summary
A backside illuminated imaging sensor with a seal ring support includes an epitaxial layer having an imaging array formed in a front side of the epitaxial layer. A metal stack is coupled to the front side of the epitaxial layer, wherein the metal stack includes a seal ring formed in an edge region of the imaging sensor. An opening is included that extends from the back side of the epitaxial layer to a metal pad of the seal ring to expose the metal pad. The seal ring support is disposed on the metal pad and within the opening to structurally support the seal ring.