Backside Image Sensor Charge Layer for High-Aspect Trench Passivation
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Solution Overview
Problem
Conventional methods for passivating the surface of backside-illuminated CMOS image sensors, such as implantation or thick dielectric layers, fail to provide sufficient charge carriers for deep pixels with high aspect ratio trench isolation, leading to noise in electrical signals and increased fabrication costs.
Innovation Solution
Epitaxially growing a charge layer directly on the surfaces of pixels and trenches within the image sensor substrate, using materials like boron-doped silicon or carbon-doped silicon, to effectively passivate dangling bonds and defect centers, thereby reducing noise in electrical signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional charge layer formation methods (implantation or thick dielectric layers) are used, then charge carriers are provided for passivation, but coverage on sidewalls of high aspect ratio trenches is insufficient or signal absorption increases
Solution Approach 1:
The patent changes the formation method parameter from implantation or thick dielectric deposition to epitaxial growth, enabling conformal coverage on high aspect ratio trench sidewalls while providing sufficient charge carriers for passivation without excessive signal absorption
Solution Approach 2:
The patent uses a composite structure combining a first charge layer formed by epitaxial growth on trench sidewalls and a second charge layer formed by implantation or dielectric deposition, where each layer complements the other to achieve comprehensive passivation
2Quantity of substance
If implantation is used to form charge layer, then charge carriers are introduced, but coverage on sidewalls of high aspect ratio trenches is poor
Solution Approach 1:
The patent changes the charge layer formation mechanism from ion implantation to epitaxial growth, which naturally conforms to complex three-dimensional surfaces including high aspect ratio trench sidewalls, achieving both sufficient charge carrier density and complete surface coverage
Solution Approach 2:
The patent addresses the three-dimensional challenge of high aspect ratio trenches by using epitaxial growth that deposits material conformally on vertical sidewalls, effectively extending coverage into the vertical dimension where implantation fails
3Reliability
If thick dielectric layer is used for charge separation, then induced charge carriers are passivated, but signal absorption increases due to high absorption coefficient
Solution Approach 1:
The patent optimizes the dielectric layer thickness parameter to be thin rather than thick, and uses epitaxial growth to achieve effective passivation with minimal material, reducing the absorption coefficient's impact on signal while maintaining charge carrier passivation effectiveness
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 epitaxially grown charge layer enhances the signal-to-noise ratio by providing a high concentration of charge carriers that recombine with noise-causing carriers, improving the performance of image sensors while maintaining reasonable fabrication costs and design requirements.
Implementation Method 1
epitaxially growing a charge layer directly on the pre-cleaned exposed surface of the sensor substrate
Implementation Method 2
Charge carriers in the charge layer recombine with charge carriers generated from the dangling bonds and/or defect centers
Implementation Method 3
using materials like boron-doped silicon or carbon-doped silicon
Implementation Method 4
A charge layer may be formed by implanting a desired type of charges (i.e., positive charges or negative charges that are opposite of the charge carriers generated from the dangling bonds and/or defect centers) into the substrate
Data Source
AI summary
A method of fabricating a semiconductor device includes forming an interconnect structure over a front side of a sensor substrate, thinning the sensor substrate from a back side of the sensor substrate, etching trenches into the sensor substrate, pre-cleaning an exposed surface of the sensor substrate, epitaxially growing a charge layer directly on the pre-cleaned exposed surface of the sensor substrate, and forming isolation structures within the etched trenches.