Backside Illuminated Image Sensor with P+ Implantation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

As image sensors and their pixels continue to shrink, they face challenges in efficiently capturing photonically generated charges, leading to reduced image quality due to increased dark current and decreased sensitivity, especially for longer wavelengths.

Innovation Solution

The implementation of a front side illuminated imaging sensor with a highly doped P+ implantation layer and optimized remaining substrate thickness, using boron implantation and laser annealing, to enhance quantum efficiency and reduce dark current, while selectively reflecting longer wavelengths back towards the front surface for improved sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If image sensors and pixels are shrunk to reduce size, then device miniaturization is achieved, but quantum efficiency decreases and dark current increases

Engineering Contradiction:

Improvesensor sizeVSAvoidimage quality

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The patent inverts the conventional light incident direction by using backside illumination instead of frontside illumination. This allows light to enter through the back surface of the substrate, bypassing metal interconnect layers and other front-side structures that block photons in miniaturized sensors, thereby maintaining quantum efficiency despite reduced sensor size

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the doping concentration parameter by forming a highly doped P+ implantation layer with concentration of 1×10^19 to 1×10^21 atoms/cm³ at the back surface. This parameter change creates strong electric field effects that suppress dark current generation while maintaining efficient charge collection, addressing the dark current issue that arises from sensor miniaturization

Inventive Principle:

Principle #35Parameter changes

2Productivity

If pixel size is reduced to increase array density, then array integration is improved, but sensitivity to longer wavelengths decreases

Engineering Contradiction:

Improvearray integrationVSAvoidwavelength sensitivity

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

By inverting the illumination direction to backside illumination, longer wavelength photons (red and near-IR) can penetrate deeper into the substrate without being blocked by front-side metal layers. This enables miniaturized pixels to maintain sensitivity to longer wavelengths while achieving high array integration

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent utilizes the substrate thickness dimension by optimizing it to 3-10 micrometers, creating a sufficient light path length for longer wavelengths to be absorbed and generate charges. This dimensional optimization enables wavelength-sensitive detection in compact pixel structures

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Length of stationary object

If substrate thickness is reduced to minimize sensor depth, then device integration is improved, but charge collection efficiency decreases

Engineering Contradiction:

Improvesubstrate thicknessVSAvoidcharge collection efficiency

Core Design Contradiction:

Length of stationary objectVSReliability

Solution Approach 1:

The patent optimizes the substrate thickness parameter to a specific range of 3-10 micrometers and forms a highly doped P+ layer at the back surface. This combination of parameters creates an efficient charge collection mechanism where the thin substrate enables device integration while the high doping concentration ensures sufficient electric field for charge collection

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The P+ implantation layer is formed in advance at the back surface before final device assembly. This preliminary action creates a built-in electric field structure that actively collects photogenerated charges, compensating for the reduced substrate thickness and maintaining collection efficiency

Inventive Principle:

Principle #10Preliminary action

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 increases quantum efficiency and spectral performance, reduces dark current, and enhances sensitivity to red and near-IR wavelengths, resulting in improved image quality by effectively capturing and processing photonically generated charges.

Implementation Method 1

selectively reflecting longer wavelengths back towards the front surface for improved sensitivity

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

using boron implantation and laser annealing

Methodology Applied

Scientific EffectIon Implantation: Ion Implantation

Implementation Method 3

using boron implantation and laser annealing

Methodology Applied

Scientific EffectLaser heating: Laser

Data Source

PatentUS8232133B2Image sensor with backside passivation and metal layer

Publication Date: 2012.07.31 OMNIVISION TECHNOLOGIES INC

AI summary

An image sensor includes a semiconductor layer that filters light of different wavelengths. For example, the semiconductor layer absorbs photons of shorter wavelengths and passes more photons of longer wavelengths such that the longer wavelength photons often pass through without being absorbed. An imaging pixel having a photodiode is formed near a front side of the semiconductor layer. A dopant layer is formed below the photodiode near a back side of the semiconductor layer. A mirror that primarily reflects photons of longer visible wavelengths is disposed on the back side of the semiconductor layer.