Backside-illuminated Image Sensor Doped Silicon Layer
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Solution Overview
Problem
Current backside-illuminated image sensor fabrication processes face challenges such as deep dopant implantation harming short wavelength quantum efficiency, incomplete dopant activation, and defects from high energy laser annealing, leading to high dark current and white pixel count issues.
Innovation Solution
A manufacturing process involving plasma-enhanced chemical vapor deposition of a doped silicon layer on the thinned substrate, followed by low-temperature laser annealing to activate dopants and reduce substrate damage, with optional anti-reflective coating application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If backside dopant implantation is performed to improve sensor performance, then quantum efficiency is improved, but dopant can go too deep and harm short wavelength quantum efficiency
Solution Approach 1:
The patent changes the doping method from ion implantation to in-situ doped PECVD, which provides better control over dopant depth and distribution. The in-situ doping process allows precise control of dopant concentration and depth profile during deposition, preventing excessive dopant penetration that would harm short wavelength quantum efficiency.
2Reliability
If high energy laser annealing is used to activate implanted dopants, then dopant activation is improved, but defects such as melting the substrate surface occur
Solution Approach 1:
The patent changes the annealing method from high energy laser annealing to low energy laser annealing or thermal annealing. This parameter change reduces the risk of substrate surface melting and defect formation while still achieving adequate dopant activation. The lower energy process maintains substrate integrity.
3Manufacturing precision
If substrate thickness is reduced to improve quantum efficiency, then color cross talk is reduced and quantum efficiency is improved, but substrate becomes more vulnerable to damage during processing
Solution Approach 1:
The patent performs doping during the thinning process itself, before the substrate becomes too thin and vulnerable. The in-situ doped PECVD is performed on the thinned substrate, allowing dopant incorporation at the precise moment when the substrate reaches the desired thin thickness, thus maintaining both quantum efficiency and substrate integrity.
4Quantity of substance
If ion implantation is used for backside doping, then dopant can be introduced, but it is difficult to activate all the backside dopant and avoid un-activated defects
Solution Approach 1:
The patent replaces the mechanical ion implantation process with a chemical vapor deposition process. The in-situ doped PECVD uses chemical reactions in the vapor phase to deposit silicon containing dopants directly into the substrate, achieving complete dopant incorporation without the activation issues associated with ion implantation.
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 process improves quantum efficiency and reduces defects, resulting in enhanced image sensor performance with lower dark current and white pixel count, while maintaining substrate integrity.
Implementation Method 1
plasma-enhanced chemical vapor deposition of a doped silicon layer on the thinned substrate
Implementation Method 2
low-temperature laser annealing to activate dopants
Implementation Method 3
low-temperature laser annealing to activate dopants
Data Source
AI summary
Embodiments of a process comprising forming a pixel on a front side of a substrate, thinning the substrate, depositing a doped silicon layer on a backside of the thinned substrate, and diffusing a dopant from the doped silicon layer into the substrate. Embodiments of an apparatus comprising a pixel formed on a front side of a thinned substrate, a doped silicon layer formed on a backside of the thinned substrate, and a region in the thinned substrate, and near the backside, where a dopant has diffused from the doped silicon layer into the thinned substrate. Other embodiments are disclosed and claimed.