Solid-State Imaging Device Photodiode Impurity Gradient

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Solution Overview

Problem

Solid-state imaging devices face challenges in reading out signal charges from deep positions within the semiconductor substrate, leading to afterimages and limited saturation charge amounts, as signal charges remain in deep regions due to potential barriers and inefficient charge transfer.

Innovation Solution

A solid-state imaging device configuration with a readout gate embedded in a trench via a gate insulating film, a floating diffusion on the surface, and a potential adjustment region adjacent to the photoelectric conversion region, allowing for deeper charge readout without disturbance, along with a manufacturing method that forms photodiodes with high impurity concentrations to enhance PN junction capacity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If multiple photodiodes are formed in the depth direction to increase saturation charge amount, then saturation charge amount is improved, but signal charges remain in deep regions causing afterimages

Engineering Contradiction:

Improvesaturation charge amountVSAvoidsignal charge readout completeness

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The photodiode structure is segmented into multiple electroconductive type regions (first, second, third regions) with different impurity concentrations arranged in the depth direction. This segmentation allows each region to contribute differently to charge accumulation and readout, enabling complete signal charge extraction while maintaining high saturation charge amount.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the photodiode are assigned different impurity concentrations: the first electroconductive type region has higher impurity concentration than the second, which in turn has higher concentration than the third. This local quality variation creates optimal conditions for both charge accumulation in deeper regions and efficient charge transfer to the surface, resolving the afterimage problem while increasing saturation charge.

Inventive Principle:

Principle #3Local quality

2Quantity of substance

If photodiodes are formed with higher impurity concentrations to enhance PN junction capacity, then saturation charge amount increases, but charge transfer efficiency to surface may be reduced

Engineering Contradiction:

Improvesaturation charge amountVSAvoidcharge transfer efficiency

Core Design Contradiction:

Quantity of substanceVSProductivity

Solution Approach 1:

The impurity concentration parameter is varied systematically across different depth regions of the photodiode. The first region (deeper) has higher impurity concentration for charge accumulation, while the third region (surface-adjacent) has lower impurity concentration to facilitate efficient charge transfer to the floating diffusion, optimizing both saturation charge amount and transfer efficiency.

Inventive Principle:

Principle #35Parameter changes

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

Enables the complete readout of signal charges from deep positions, preventing afterimages and increasing saturation charge amounts, thereby improving imaging properties and signal processing efficiency.

Implementation Method 1

a photoelectric conversion region provided within the semiconductor substrate

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Implementation Method 2

a readout gate embedded within a trench formed in a semiconductor substrate via a gate insulating film

Methodology Applied

Scientific EffectElectrical insulation: Dielectric

Implementation Method 3

a first photodiode made up of a first first-electroconductive-type semiconductor region formed on a first principal face side of a semiconductor substrate, and a first second-electroconductive-type semiconductor region formed within the semiconductor substrate adjacent to the first first-electroconductive-type semiconductor region

Methodology Applied

Scientific EffectPN junction formation: Diode

Data Source

PatentUS11315968B2Solid state image device having an impurity concentration at a p/n interface of one photodiode being equal to or greater than at p/n interface of another photodiode within a semiconductor substrate

Publication Date: 2022.04.26 SONY GROUP CORP

AI summary

A solid-state imaging device includes: a first photodiode made up of a first first-electroconductive-type semiconductor region formed on a first principal face side of a semiconductor substrate, and a first second-electroconductive-type semiconductor region formed within the semiconductor substrate adjacent to the first first-electroconductive-type semiconductor region; a second photodiode made up of a second first-electroconductive-type semiconductor region formed on a second principal face side of the semiconductor substrate, and a second second-electroconductive-type semiconductor region formed within the semiconductor substrate adjacent to the second first-electroconductive-type semiconductor region; and a gate electrode formed on the first principal face side of the semiconductor substrate; with impurity concentration of a connection face between the second first-electroconductive-type semiconductor region and the second second-electroconductive-type semiconductor region being equal to or greater than impurity concentration of a connection face of an opposite layer of the second first-electroconductive-type semiconductor region of the second second-electroconductive-type semiconductor region.