Interpixel Trench PN Junction Layout for Dark Current Suppression

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Solution Overview

Problem

Existing imaging element structures face issues such as weakened silicon substrate pinning, charge flow into photodiodes, deterioration of Dark characteristics, and restrictions on element arrangement due to trench formation between pixels.

Innovation Solution

The implementation of a first imaging element with a photoelectric conversion unit, a through trench penetrating a semiconductor substrate, and a PN junction region formed by a P-type and an N-type region in the side wall of the through trench, where the through trench has a partial opening portion and the P-type region is formed in this opening portion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a trench is formed between pixels to isolate them, then charge isolation is improved, but element arrangement freedom is restricted

Engineering Contradiction:

Improvecharge isolationVSAvoidelement arrangement freedom

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The invention extracts the light-shielding function from the trench structure itself and relocates it to a separate light-shielding film formed on the trench. This allows the trench to be shallower and partially open, removing the constraint that forced complete pixel isolation and enabling greater element arrangement freedom while maintaining charge isolation through the combined trench-film structure.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The light-shielding film serves multiple functions: it provides optical isolation between pixels, enables the trench to be partially open rather than fully enclosed, and allows transistor gates to be formed in the trench region. This multi-functionality resolves the contradiction by making the trench structure adaptable to different element arrangements.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If a trench is formed between pixels, then optical isolation is improved, but the number of contacts increases

Engineering Contradiction:

Improveoptical isolationVSAvoidnumber of contacts

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention merges the light-shielding function with the trench structure by forming a light-shielding film on the trench. This combination allows the trench to serve both as a mechanical support and an optical isolation structure, reducing the need for additional deep contacts while maintaining effective pixel isolation.

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If the trench is completely closed, then charge holding is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvecharge holdingVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention extracts the light-shielding function from the trench walls and places it on a separate film formed on the trench. This allows the trench to be partially open rather than completely enclosed, simplifying the manufacturing process by eliminating the need to form and fill deep trenches while maintaining effective charge holding through the light-shielding film.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The light-shielding film is formed on the trench before final processing steps, preliminarily establishing the optical isolation and enabling subsequent steps like transistor gate formation in the trench region. This preliminary action simplifies overall manufacturing by setting up the structure in an optimal sequence.

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 configuration suppresses deterioration of Dark characteristics and increases the degree of freedom in arranging imaging elements by forming a strong electric field region and reducing the number of contacts.

Implementation Method 1

a PN junction region configured by a P-type region and an N-type region in a side wall of the through trench

Methodology Applied

Scientific EffectPN junction:

Implementation Method 2

form a strong electric field region and hold charges in the strong electric field region

Methodology Applied

Scientific EffectElectric field: Electric Field

Implementation Method 3

a photoelectric conversion unit configured to perform photoelectric conversion

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS12211875B2Imaging element having p-type and n-type solid phase diffusion layers formed in a side wall of an interpixel light shielding wall

Publication Date: 2025.01.28 SONY SEMICON SOLUTIONS CORP

AI summary

The present technology relates to an imaging element that can increase the degree of freedom of element arrangement. A photoelectric conversion unit, a through trench penetrating a semiconductor substrate in a depth direction and formed between pixels each including the photoelectric conversion unit, and a PN junction region in a side wall of the trench are included, and the through trench has an opening portion, and a P-type region is formed in the opening portion. A photoelectric conversion unit, a holding unit, a through trench formed between the photoelectric conversion unit and the holding unit, and a PN junction region in a side wall of the through trench are included, and the through trench has an opening portion and a readout gate for reading the charge from the photoelectric conversion unit is formed in the opening portion. The present technology can be applied to, for example, an imaging element.