Image Sensor Sidewall Passivation Using Hydrogenated Amorphous Silicon
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Solution Overview
Problem
Aluminum oxide passivation layers in image sensors do not provide sufficient passivation along the substrate sidewalls, especially when n-type doping is present, leading to reduced electron barrier height and increased photo-generated electron recombination, and high temperature anneal processes are not feasible for all fabrication processes due to heat exposure limitations.
Innovation Solution
The use of hydrogenated amorphous silicon as a passivation layer with controlled dopant and hydrogen concentrations to form an effective electron barrier and provide additional hydrogen ions for defect passivation, reducing recombination and eliminating the need for high temperature anneal processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum oxide passivation layers are used in image sensors, then passivation is provided, but the electron barrier height is reduced and photo-generated electron recombination increases when n-type doping is present
Solution Approach 1:
The patent changes the material composition parameters of the passivation layer by incorporating hydrogenated amorphous silicon with controlled dopant and hydrogen concentrations into the aluminum oxide passivation layer. This parameter modification enables the layer to maintain passivation functionality while increasing electron barrier height and reducing photo-generated electron recombination that occurs with standard aluminum oxide layers combined with n-type doping
Solution Approach 2:
The patent creates a composite passivation structure by combining aluminum oxide with hydrogenated amorphous silicon. This composite material approach allows the passivation layer to simultaneously provide the dielectric properties of aluminum oxide and the electron barrier enhancement and recombination reduction properties of hydrogenated amorphous silicon, resolving the contradiction between passivation quality and electron recombination loss
2Reliability
If high temperature anneal processes are used to improve passivation, then passivation quality improves, but heat exposure limitations prevent use in all fabrication processes
Solution Approach 1:
The patent incorporates hydrogen ions into the passivation layer structure during the deposition process itself, performing the passivation action in advance rather than requiring subsequent high temperature annealing. This preliminary incorporation of hydrogen ions during low-temperature deposition achieves effective passivation without exposing the substrate to high temperatures that would limit fabrication process compatibility
3Reliability
If n-type doping is used in the substrate, then electrical performance improves, but electron barrier height is reduced leading to increased recombination
Solution Approach 1:
The patent introduces hydrogenated amorphous silicon as an intermediary layer between the n-type doped substrate and the aluminum oxide passivation layer. This intermediary layer maintains the electrical performance benefits of n-type doping while providing an additional electron barrier that prevents photo-generated electrons from recombining at the substrate-passivation interface, thus resolving the contradiction between electrical performance and recombination loss
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 approach enhances the passivation of image sensor substrates by reducing electron and hole recombination, improving image sensor performance, and allowing for fabrication processes with limited heat exposure.
Implementation Method 1
The first passivation layer comprises hydrogenated amorphous silicon... provide additional hydrogen ions for defect passivation
Implementation Method 2
form an effective electron barrier and providing additional hydrogen ions for defect passivation, reducing recombination
Data Source
AI summary
The present disclosure relates to an integrated chip including a substrate. A photodetector is arranged within the substrate. A trench isolation structure extends into the substrate on opposite sides of the photodetector. The trench isolation structure separates the photodetector from neighboring photodetectors. A first passivation layer is between a sidewall of the substrate and a sidewall of the trench isolation structure. The first passivation layer includes hydrogenated amorphous silicon.