Solid state image sensor and method of manufacturing solid state image sensor
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Solution Overview
Problem
Conventional solid state image sensors face limitations in reducing the area of the floating diffusion portion due to alignment margin restrictions and mask size constraints for forming metal contacts, which hinders pixel miniaturization and high conversion efficiency.
Innovation Solution
A solid state image sensor design featuring a transfer gate, a floating diffusion portion, and an extraction electrode made of conductive materials like N-type polysilicon, surrounded by insulating material, allowing self-aligned formation and reducing the distance between transfer gates, thereby increasing parasitic capacitance and enhancing transfer performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional ion implantation is used to form the floating diffusion portion, then the process is simple, but the mean projected range Rp is small and variation in buffer film thickness causes variation in implantation depth
Solution Approach 1:
The patent applies preliminary action by forming a mask film pattern before ion implantation. The mask film with predetermined pattern is formed on the semiconductor substrate, and ion implantation is then performed through this mask. This preliminary masking action enables precise control of implantation depth and pattern, resolving the precision issue while maintaining process simplicity.
2Area of moving object
If the area of the floating diffusion portion is reduced to enable pixel miniaturization, then the photodetector area increases, but the distance between the transfer gate and sidewall becomes too small for contact alignment
Solution Approach 1:
The patent resolves the alignment margin problem by transitioning to a self-aligned process in the vertical dimension. The mask film is formed to extend in the vertical direction, and the contact is formed through self-alignment with this vertical mask structure. This dimensional transition eliminates the need for lateral alignment margins, enabling floating diffusion portion miniaturization while maintaining ease of manufacture.
Solution Approach 2:
The patent applies self-service through self-aligned contact formation. The contact is formed using the mask film structure itself as the alignment reference, without requiring separate alignment steps. The mask film pattern automatically defines the contact position, enabling precise contact formation even when the floating diffusion portion area is minimized.
3Reliability
If the floating diffusion portion area is reduced to improve conversion efficiency, then the capacity decreases, but mask size restrictions prevent further reduction
Solution Approach 1:
The patent overcomes mask size constraints by forming the mask film with vertical extension. The mask film is deposited and patterned to extend vertically, allowing the contact opening to be formed through self-alignment without being limited by lateral mask dimensions. This enables continuous reduction of floating diffusion portion area to improve conversion efficiency.
Solution Approach 2:
The patent applies parameter changes by modifying the mask film formation parameters. Instead of using conventional lateral mask patterns, the mask film is formed with controlled vertical thickness and extension. This parameter change in mask film geometry enables self-aligned contact formation and removes the constraint of mask size, allowing floating diffusion portion miniaturization for improved conversion efficiency.
4Area of stationary object
If the distance between transfer gate and sidewall is reduced to minimize floating diffusion area, then pixel size decreases, but alignment margin for contact formation is lost
Solution Approach 1:
The patent applies self-service by making the contact formation process self-aligned. The mask film structure automatically serves as the alignment reference for contact formation. The contact is formed through etching or deposition processes that use the vertical mask film as the defining structure, eliminating the need for separate alignment steps and ensuring high precision even when the distance between transfer gate and sidewall is minimized.
Solution Approach 2:
The patent applies preliminary action by pre-forming the mask film pattern that defines both the floating diffusion portion boundary and the contact position. This preliminary mask formation establishes the precise geometric relationship between components before any contact formation steps, ensuring alignment precision is maintained even when pixel size is reduced to minimum dimensions.
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 configuration enables the miniaturization of the floating diffusion portion, improves transfer performance, and achieves high conversion efficiency while reducing alignment restrictions and ion implantation variations.
Implementation Method 1
a photodetector (PD) region
Implementation Method 2
a floating diffusion portion that converts signal charge transferred from a photodiode via the transfer gate into a voltage signal
Data Source
AI summary
A solid state image sensor according to an embodiment includes a transfer gate, a floating diffusion portion that converts signal charge transferred from a photodiode via the transfer gate into a voltage signal, and an extraction electrode that is formed of a film of conductive material including any of amorphous silicon, monocrystalline silicon, or N+ polysilicon, that has a peripheral edge portion surrounded by a film of insulating material and one end electrically connected to the floating diffusion portion, and that transmits the voltage signal.