CMOS Image Sensor Light Shielding for Memory Node Leakage
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Solution Overview
Problem
Current metal light-shielding technologies in Global Shutter (GS) CMOS image sensors are inadequate in reducing parasitic light leakage to memory nodes, leading to contamination of photo-generated charges and artifacts, and may cause plasma damage during fabrication.
Innovation Solution
A method involving a metal light-shielding structure fabricated over the memory node using a tungsten (W) metal layer, integrated within the interlayer dielectric (ILD) layer, which is patterned to prevent incident light from reaching the memory node and transfer gate, thereby reducing light-induced noise and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If metal light-shielding is engineered on the memory node, then light leakage reduction is improved, but plasma damage to the memory node occurs during fabrication
Solution Approach 1:
A light-shielding structure comprising a first light-shielding layer and a second light-shielding layer is introduced as an intermediary between the incident light and the memory node. The first light-shielding layer is positioned closer to the incident light source, while the second light-shielding layer is positioned closer to the memory node, creating a staged shielding approach that reduces light leakage without requiring direct metal contact with the memory node, thereby preventing plasma damage
Solution Approach 2:
The light-shielding function is segmented into two separate layers instead of using a single metal layer. The first light-shielding layer handles the primary light blocking, while the second light-shielding layer provides additional shielding close to the memory node. This segmentation allows each layer to be optimized for its specific position and function, reducing the need for heavy metal shielding that would cause plasma damage
2Device complexity
If rolling shutter pulses are used, then circuit complexity is reduced, but light-induced noise increases due to parasitic light contamination
Solution Approach 1:
The light-shielding structure acts as an intermediary that physically blocks parasitic light from reaching the memory node, thereby reducing light-induced noise while maintaining the simplicity of the rolling shutter pulse circuit. The shielding structure includes a first light-shielding layer and a second light-shielding layer positioned at different locations to effectively block light paths without requiring additional complex circuitry
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 solution effectively minimizes parasitic light leakage, enhancing the signal-to-noise ratio and preventing plasma damage, resulting in improved image quality and reduced artifacts in GS CMOS image sensors.
Implementation Method 1
a metal light-shielding structure fabricated over the memory node using a tungsten (W) metal layer, integrated within the interlayer dielectric (ILD) layer, which is patterned to prevent incident light from reaching the memory node and transfer gate
Data Source
AI summary
Disclosed is a CMOS image sensor with global shutters and a method for fabricating the CMOS image sensor. In one embodiment, a semiconductor device, includes: a light-sensing region; a charge-storage region; a light-shielding structure; and at least one via contact; wherein the charge-storage region is spatially configured adjacent to the light-sensing region in a lateral direction, wherein the light-shielding structure is configured over the charge-storage region in a vertical direction so as to prevent incident light leaking from the light-sensing region to the signal-processing region, wherein the light-shielding structure is configured in an interlayer dielectric (ILD) layer, and wherein the light-shielding structure is simultaneously formed with the at least one via contact.