Backside Illuminated Sensor Reinforced Pad Structure
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Solution Overview
Problem
Backside illuminated imaging sensors face challenges with wafer thinning, which increases susceptibility to physical damage during manufacturing due to limited structural support for metal pads, affecting their integrity during bonding and testing processes.
Innovation Solution
A reinforced pad structure is introduced by forming a reinforcing frame within the openings for wire bonding, using a metal, nitride, or oxide film deposited on the backside of the wafer, which is then etched to create a frame shape that strengthens the metal pads and provides structural support, allowing for improved durability during bonding and testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the wafer thickness is reduced to improve sensitivity, then the sensitivity is improved, but the wafer becomes more susceptible to physical damage during manufacturing
Solution Approach 1:
The patent applies local quality by creating a reinforced pad structure only at specific locations where metal pads are positioned, rather than uniformly thickening the entire wafer. This localized reinforcement provides structural support where needed while maintaining thin wafer thickness for light sensitivity in other areas.
Solution Approach 2:
The patent uses composite materials by combining the thin semiconductor wafer with a reinforcing material (such as glass, ceramic, or polymer) to create a composite structure. This composite approach allows the wafer to maintain thinness for sensitivity while the reinforcing material provides the necessary structural strength.
2Measurement precision
If the wafer is thinned to improve sensitivity, then the sensitivity is improved, but the metal pads lack structural support during bonding and testing
Solution Approach 1:
The patent applies preliminary action by forming the reinforced pad structure before wire bonding and testing processes. This pre-reinforcement ensures that the metal pads have adequate structural support during subsequent bonding and testing operations, preventing pad damage before it can occur.
Solution Approach 2:
The reinforcing pad structure acts as a cushioning element that protects the metal pads from mechanical stress during bonding and testing. This beforehand cushioning prevents pad damage by absorbing or distributing the mechanical loads that would otherwise be applied directly to the thin wafer and metal pads.
3Strength
If a reinforced pad structure is added to strengthen metal pads, then the mechanical strength is improved, but the device complexity increases
Solution Approach 1:
The patent uses thin film reinforcement structures that are deposited or formed as thin layers over the metal pads. These thin films provide mechanical reinforcement without adding significant thickness or complexity to the overall device structure, maintaining a relatively simple device architecture while improving pad strength.
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
The reinforced pad structure enhances the mechanical strength of the metal pads, enabling them to withstand wire bond pulling and shear testing, thereby improving the reliability and durability of backside illuminated imaging sensors.
Implementation Method 1
a metal, nitride, or oxide film deposited on the backside of the wafer, which is then etched to create a frame shape
Implementation Method 2
a metal, nitride, or oxide film deposited on the backside of the wafer, which is then etched to create a frame shape
Data Source
AI summary
A method of fabricating a backside illuminated imaging sensor that includes a device layer, a metal stack, and an opening is disclosed. The device layer has an imaging array formed in a front side of the device layer, where the imaging array is adapted to receive light from a back side of the device layer. The metal stack is coupled to the front side of the device layer and includes at least one metal interconnect layer having a metal pad. The opening extends from the back side of the device layer to the metal pad to expose the metal pad for wire bonding. The method includes depositing a film on the back side of the device layer and within the opening, then etching the film to form a frame within the opening to structurally reinforce the metal pad.