Buried Conductive Layer Composition for Low-Noise Image Sensors
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Solution Overview
Problem
Existing image sensors face performance issues due to the formation of voids or seams in the buried conductive layer within pixel trenches, which can lead to increased dark current and noise levels, especially during heat treatment processes.
Innovation Solution
Incorporating polysilicon with fining elements such as oxygen, carbon, or fluorine into the buried conductive layer, which helps maintain a small grain size and prevents grain growth or coalescence, thereby avoiding void formation and enhancing the image sensor's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment process is applied to the buried conductive layer, then electrical conductivity is improved, but grain growth occurs causing void formation and dark current increase
Solution Approach 1:
The patent changes the chemical composition parameters of the polysilicon by incorporating fining elements (oxygen, carbon, or fluorine) at specific concentrations. This compositional modification allows the material to maintain small grain size even after heat treatment, resolving the contradiction between improving electrical conductivity through heat treatment and preventing grain growth that causes void formation.
Solution Approach 2:
The patent creates a composite material structure by combining polysilicon with fining elements (oxygen, carbon, or fluorine). This composite approach enables the buried conductive layer to simultaneously achieve good electrical conductivity and maintain fine grain structure after heat treatment, preventing the void formation that occurs with conventional polysilicon.
2Reliability
If polysilicon is used in the buried conductive layer, then electrical conductivity is achieved, but voids and seams form during heat treatment increasing dark current
Solution Approach 1:
The patent modifies the chemical composition of polysilicon by adding fining elements (oxygen, carbon, or fluorine) at controlled concentrations. This parameter change prevents void and seam formation during heat treatment, thereby eliminating the harmful effects of dark current and noise while maintaining electrical conductivity.
Solution Approach 2:
The patent converts the typically harmful presence of impurities in polysilicon into a beneficial feature by intentionally incorporating fining elements (oxygen, carbon, or fluorine). These elements, which would normally be considered contaminants, are now used to prevent void formation and reduce dark current, transforming a harmful factor into a benefit.
3Stability of the object's composition
If grain growth is allowed during heat treatment, then denser structure is achieved, but voids and seams form reducing image sensor performance
Solution Approach 1:
The patent changes the compositional parameters of the polysilicon by incorporating fining elements, which fundamentally alter the heat treatment behavior. Instead of undergoing grain growth that leads to void formation, the modified polysilicon maintains a fine-grained dense structure, simultaneously achieving structural density and preventing voids and seams.
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 use of polysilicon with fining elements in the buried conductive layer prevents the formation of voids and seams, improving the image sensor's performance by reducing dark current and noise levels, and maintaining image quality.
Implementation Method 1
the buried conductive layer includes polysilicon including the fining element at a first concentration... maintains a small grain size and prevents grain growth or coalescence
Data Source
AI summary
An image sensor including a semiconductor substrate having a first surface and a second surface; and a pixel isolation film extending from the first surface of the semiconductor substrate into the semiconductor substrate and defining active pixels in the semiconductor substrate, wherein the pixel isolation film includes a buried conductive layer including polysilicon containing a fining element at a first concentration; and an insulating liner between the buried conductive layer and the semiconductor substrate, and wherein the fining element includes oxygen, carbon, or fluorine.