Backside Illuminated Sensor Dipole Modulating Layer Dark Current
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Solution Overview
Problem
Existing methods for forming backside illuminated CMOS image sensors fail to effectively control the electrostatic charge at the interface between the photodiode and the dielectric layer, leading to persistent dark current issues.
Innovation Solution
A method involving the deposition of a dipole modulating layer and a fixed charge layer, with specific thickness and placement control, using oxides such as titanium or aluminum oxides to shift the flatband voltage and reduce dark current, is introduced. This includes forming a photodiode on a substrate with an oxide layer, followed by a thin insulator comprising a dipole modulating layer positioned between two fixed charge sub-layers, and an antireflective coating to enhance photoelectron injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a dielectric film with fixed negative charges is deposited above the photodiode to suppress dark current, then dark current suppression is improved, but the electrostatic effect at the interface cannot be fully eliminated and control is limited
Solution Approach 1:
The dielectric film is segmented into multiple functional layers: a first dielectric layer with first fixed negative charges, a second dielectric layer with second fixed negative charges, and an intermediate layer between them. This segmentation allows independent control of electrostatic effects at different interfaces, enabling suppression of dark current while providing tunable electrostatic control through adjustment of individual layer properties.
Solution Approach 2:
The patent employs a composite dielectric structure combining multiple dielectric materials with different electrical properties. The first and second dielectric layers have different fixed charge densities and electrical characteristics, creating a composite structure that simultaneously achieves dark current suppression and tunable electrostatic control. The intermediate layer further modifies the composite structure to optimize interface properties.
2Adaptability or versatility
If hafnium oxide films with varying thickness or implant conditions are used to control electrostatic charge, then some control is achieved, but precise control for a given film thickness remains difficult
Solution Approach 1:
The dielectric film is divided into multiple layers with distinct fixed charge densities. By independently controlling the thickness and charge density of each layer (first dielectric layer, second dielectric layer, intermediate layer), precise control of the overall electrostatic effect is achieved for a given total film thickness. This segmentation transforms a single-degree-of-freedom control problem into a multi-degree-of-freedom system.
Solution Approach 2:
The patent utilizes parameter changes in multiple dimensions: fixed charge density of each layer, thickness of each layer, and material composition. By adjusting these parameters independently, precise control of the electrostatic effect is achieved. For example, the first dielectric layer can have a higher fixed charge density to suppress dark current, while the second dielectric layer is optimized for other performance characteristics.
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 solution effectively reduces dark current by engineering the electrostatic effect, allowing for precise control of the charge distribution and enhancing the performance of backside illuminated image sensors.
Implementation Method 1
a dipole modulating layer and a fixed charge layer... effectively reduces dark current by engineering the electrostatic effect
Implementation Method 2
This dielectric film, frequently made of hafnium oxide, often has fixed negative charges to create a hole accumulation layer
Implementation Method 3
using oxides such as titanium or aluminum oxides to shift the flatband voltage and reduce dark current
Implementation Method 4
an antireflective coating to enhance photoelectron injection
Implementation Method 5
backside illuminated image sensors... photodiode... direct light toward the photodiode
Data Source
AI summary
Backside illuminated sensors and methods of manufacture are described. Specifically, a backside illuminated sensor with a dipole modulating layer near the photodiode is described.