Self-Aligned Photodiode Sensor Manufacturing via Thick Oxide Replacement
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Solution Overview
Problem
Existing photodiode sensors face challenges with charge transfer due to the difference in position between the volume channel of the photodiode and the surface channel of the transistor, leading to poor charge transfer efficiency, and the manufacturing process is complex with imprecise definition of regions and encroachment issues.
Innovation Solution
A method involving the formation of a thick oxide insulation region using the LOCOS method, which self-aligns the diode and transistor regions without the need for precise implantation masks, allowing for precise definition of diode regions and subsequent replacement of the insulation region with the transistor gate, facilitating precise positioning and improved charge transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If implantation masks are used to define diode and transistor regions, then manufacturing process can be implemented, but manufacturing precision deteriorates due to imprecise definition of regions and encroachment issues
Solution Approach 1:
A thick oxide layer is introduced as an intermediary element between the substrate and the active regions. This oxide layer serves as a self-aligned reference structure that defines the boundaries of the pinning layer and accumulation region without requiring additional implantation masks, thereby eliminating mask alignment errors and region encroachment
Solution Approach 2:
The thick oxide layer is formed preliminarily before defining the active regions. This preliminary structure establishes a fixed reference framework that guides subsequent self-aligned implantations, ensuring precise spatial relationships between the pinning layer, accumulation region, and transistor gate without requiring multiple mask alignments
2Reliability
If the gate is positioned to enable charge transfer from the accumulation region, then charge transfer efficiency improves, but manufacturing complexity increases due to multiple implantation masks and alignment requirements
Solution Approach 1:
The thick oxide layer acts as a mediator that establishes a self-aligned reference structure, eliminating the need for multiple implantation masks and complex alignment procedures while maintaining the precise spatial relationship between the gate and accumulation region required for efficient charge transfer
Solution Approach 2:
The functions of multiple implantation masks and the thick oxide reference structure are merged into a single self-aligned manufacturing approach. The thick oxide layer simultaneously serves as both the reference structure and the alignment guide for all subsequent implantations, simplifying the overall manufacturing process
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 method enhances charge transfer efficiency by ensuring precise alignment and definition of diode and transistor regions, reducing manufacturing complexity and improving the accuracy of charge transfer in photodiode sensors.
Implementation Method 1
forming an insulation region (214) on a substrate (200), with the insulation region (214) preferably being a thick oxide region obtained by a LOCOS method
Implementation Method 2
when photons strike an upper surface (118) of the diode, electron-hole pairs are generated in the diode, in the regions (108, 106) and (100) and the electrons are stored here in the N region (108)
Data Source
AI summary
A method of manufacturing a photodiode sensor and an associated charge transfer transistor includes forming an insulation region on a substrate, forming the diode on a first side of the insulation region with the diode being self-aligned on the insulation region, and replacing the insulation region by a gate of the charge transfer transistor. The invention has particular utility in the manufacture of CMOS or CCD image sensors.