Backside Illuminated Imager Structure for Quantum Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current front-illuminated CMOS imagers suffer from poor quantum efficiency, increased optical cross-talk, and poor angular response due to the increased distance light travels through multiple dielectric and metal layers, leading to reduced sensitivity and efficiency as pixel size scales.
Innovation Solution
A backside illuminated imager structure is developed using a wafer-level process with a thermal oxide layer buried between the silicon wafer and device silicon, allowing for direct light coupling to the photodetector without passing through thick interlayer dielectrics, enabling a 100% optical fill factor and reduced aspect ratio, along with integration of anti-reflection coatings and microlenses for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If front-illuminated structure is used, then manufacturing process is simple, but quantum efficiency deteriorates due to increased light travel distance through multiple layers
Solution Approach 1:
The patent inverts the traditional front-illuminated structure to a backside-illuminated structure, where light enters through the back of the substrate rather than the front. This inversion eliminates the need for light to traverse multiple metal interconnect layers and dielectric layers, directly addressing the quantum efficiency problem while maintaining manufacturing compatibility through adapted fabrication processes
2Productivity
If pixel size is scaled down, then device density increases, but quantum efficiency deteriorates due to increased aspect ratio
Solution Approach 1:
By inverting the illumination direction to backside illumination, the patent eliminates the aspect ratio problem that plagues scaled-down front-illuminated pixels. The light path no longer depends on the thickness of metal and dielectric layers, allowing pixel density to increase without sacrificing quantum efficiency
3Adaptability or versatility
If multiple metal interconnect layers are added, then device functionality is improved, but angular response deteriorates due to increased reflections and obscurations
Solution Approach 1:
By inverting the illumination direction, the patent allows multiple metal interconnect layers to be present for device functionality while eliminating their harmful effects on angular response. The light enters through the substrate back, bypassing all metal layers entirely, thus maintaining wide angular acceptance without reflections or obscurations
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 achieves high quantum efficiency, excellent angular response, and low optical cross-talk, enabling superior sensitivity and image quality by eliminating unwanted reflections and absorptions, and is compatible with next-generation metals and low-k dielectrics.
Implementation Method 1
providing a wafer comprising an oxide layer buried between silicon wafer and device silicon, the oxide layer adapted to form a passivation layer in the imaging structure
Implementation Method 2
The photodetector 10 comprises an ion-implanted cathode 20 on an epitaxial or substrate silicon layer 30 that acts as the anode
Data Source
AI summary
A method for implementation of back-illuminated CMOS or CCD imagers. An oxide layer buried between silicon wafer and device silicon is provided. The oxide layer forms a passivation layer in the imaging structure. A device layer and interlayer dielectric are formed, and the silicon wafer is removed to expose the oxide layer.