Backside Image Sensor Shielding Layout for ESD Yield Protection
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Solution Overview
Problem
During the manufacturing process of backside illuminated CMOS image sensors, electrostatic charges are often accumulated, leading to potential damage of the pixel array through arcing, which decreases the yield of the sensor.
Innovation Solution
A conductive shielding layer is formed on the dielectric layer to shield the structures underneath from outer applied electric fields, reducing or preventing discharging damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If backside illumination technology is used to improve pixel sensitivity, then light sensitivity is improved, but electrostatic charge accumulation occurs during manufacturing leading to arcing damage
Solution Approach 1:
A conductive shielding layer is introduced as an intermediary component between the dielectric layer and the pixel array. This shielding layer acts as a mediator that intercepts and dissipates electrostatic charges before they can accumulate and cause arcing damage to the pixel array, thereby resolving the contradiction between maintaining manufacturing reliability and using backside illumination technology.
Solution Approach 2:
The conductive shielding layer is formed on the dielectric layer before subsequent manufacturing steps that may generate electrostatic charges. This preliminary protective action ensures that when electrostatic charges are generated during later processing, they are immediately dissipated through the shielding layer, preventing accumulation and arcing damage before they can occur.
2Reliability
If a conductive shielding layer is added to prevent electrostatic discharge, then manufacturing yield is improved, but device complexity increases
Solution Approach 1:
The conductive shielding layer is formed by modifying the electrical conductivity parameter of the existing dielectric layer through doping or material substitution, rather than adding a completely separate layer. This parameter change approach maintains the protective function while minimizing increases in device complexity and layer count.
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 conductive shielding layer effectively reduces the risk of electrostatic discharge, protecting the pixel array and improving the manufacturing yield of backside illuminated CMOS image sensors.
Implementation Method 1
a conductive shielding layer is formed on the dielectric layer to shield the structures underneath from outer applied electric field
Data Source
AI summary
An image sensor includes a pixel array, a dielectric layer, a plurality of first conductive shielding regions, and a plurality of second conductive shielding regions. The pixel array includes photodiodes within a substrate. The dielectric layer is over the substrate. From a plan view, the first conductive shielding regions are adjacent four corners of the pixel array, and the second conductive shielding regions are adjacent four sides of the pixel array. The second conductive region has a length-to-width ratio greater than a length-to-width ratio of the first conductive region.