Pixel Sensor Fluorine Passivation for Dark Current Reduction
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Solution Overview
Problem
Pixel sensors in CMOS image sensors experience dark current due to silicon dangling bonds, leading to noise and defects in images, which existing technologies have not effectively addressed.
Innovation Solution
The formation of silicon-fluorine bonds through fluorine implantation or semiconductor processing operations in regions like transfer gate contacts and shallow trench isolation areas reduces electron-hole pair generation, thereby passivating the silicon dangling bonds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pixel sensor structures are used, then manufacturing is simpler, but dark current increases due to silicon dangling bonds
Solution Approach 1:
Fluorine implantation is performed before transferring the pixel sensor to the final substrate, pre-passivating the silicon dangling bonds at the interface between the pixel sensor and substrate. This preliminary action prevents dark current generation before the sensor is assembled into the final device, resolving the contradiction by adding a simple preprocessing step that delivers significant dark current reduction without complicating the overall device structure
Solution Approach 2:
The patent changes the chemical state of the silicon surface by introducing fluorine atoms that form silicon-fluorine bonds, altering the electrical properties of the interface. This parameter change (from pure silicon to fluorinated silicon) reduces the density of states at the interface, thereby reducing dark current while maintaining manufacturing simplicity
2Reliability
If no passivation is applied, then processing is simpler, but dark signal non-uniformity increases
Solution Approach 1:
The fluorine implantation is performed as a preliminary step before final assembly, ensuring uniform passivation across all pixel elements. This preliminary treatment ensures that all regions of the pixel sensor receive consistent passivation, reducing dark signal non-uniformity while adding minimal processing steps
Solution Approach 2:
The patent replaces complex mechanical or chemical passivation methods with ion implantation, a well-established semiconductor processing technique. This substitution achieves uniform passivation through controlled ion delivery, improving dark signal uniformity while maintaining ease of manufacture through standardization
3Reliability
If silicon dangling bonds are not passivated, then device structure is simpler, but white pixel defects increase
Solution Approach 1:
Fluorine implantation is performed before final device assembly, pre-passivating the silicon surface to prevent white pixel defects. This preliminary action addresses the defect mechanism at its source without requiring additional structural elements in the final device, maintaining structural simplicity while improving reliability
Solution Approach 2:
Fluorine atoms act as an intermediary substance that bonds to silicon dangling bonds, creating a stable silicon-fluorine interface. This intermediary layer prevents the formation of defect states that would lead to white pixel defects, resolving the contradiction by introducing a simple chemical intermediary rather than complex structural modifications
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
This approach decreases dark current by approximately 13% or more, reduces dark signal non-uniformity by 25% or more, and decreases white pixels by 20% or more, enhancing the performance of pixel arrays under dark and white pixel conditions without increasing processing complexity.
Implementation Method 1
The formation of silicon-fluorine bonds through fluorine implantation or semiconductor processing operations in regions like transfer gate contacts and shallow trench isolation areas reduces electron-hole pair generation
Implementation Method 2
The formation of silicon-fluorine bonds through fluorine implantation or semiconductor processing operations in regions like transfer gate contacts and shallow trench isolation areas reduces electron-hole pair generation, thereby passivating the silicon dangling bonds
Data Source
AI summary
Implementations described herein reduce electron-hole pair generation due to silicon dangling bonds in pixel sensors. In some implementations, the silicon dangling bonds in a pixel sensor may be passivated by silicon-fluorine (Si—F) bonding in various portions of the pixel sensor such as a transfer gate contact via or a shallow trench isolation region, among other examples. The silicon-fluorine bonds are formed by fluorine implantation and/or another type of semiconductor processing operation. In some implementations, the silicon-fluorine bonds are formed as part of a cleaning operation using fluorine (F) such that the fluorine may bond with the silicon of the pixel sensor. Additionally, or alternatively, the silicon-fluorine bonds are formed as part of a doping operation in which boron (B) and/or another p-type doping element is used with fluorine such that the fluorine may bond with the silicon of the pixel sensor.