Pixel Separation Groove Insulation for Low-Dark-Current Image Sensors

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Solution Overview

Problem

In solid-state image pickup devices, dry etching for forming pixel separation grooves leads to crystal defects and dangling bonds on the semiconductor substrate surfaces, resulting in increased dark current generation due to interface state enhancements.

Innovation Solution

A laminated fixed charge film is formed on the semiconductor substrate, comprising a first insulating film provided contiguously from the light-receiving surface to the wall and bottom surfaces of the pixel separation groove, and a second insulating film on the light-receiving surface, using different deposition methods such as ALD or MOCVD for the first film and PVD for the second film, to improve interface states and suppress dark current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If dry etching is used to form pixel separation grooves, then the groove formation is achieved, but crystal defects and dangling bonds are generated on the semiconductor substrate surface, leading to increased dark current

Engineering Contradiction:

Improvegroove formationVSAvoiddark current generation

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

A fixed charge film is introduced as an intermediary layer between the semiconductor substrate and the external environment. This film compensates for the harmful effects of dry etching by providing fixed charges that reduce interface states and suppress dark current generation at the groove surfaces, while allowing the dry etching process to continue for efficient groove formation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention converts the harmful crystal defects and dangling bonds generated by dry etching into beneficial effects by forming a fixed charge film that specifically targets these defect regions. The fixed charges in the film compensate for the interface states created by etching, transforming the harmful surface conditions into an opportunity for enhanced dark current suppression through strategic charge placement.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Device complexity

If a single-layer fixed charge film is formed on the semiconductor substrate, then the film formation is simplified, but the interface states at the groove surfaces are not sufficiently reduced, leading to inadequate dark current suppression

Engineering Contradiction:

Improvefilm structureVSAvoiddark current generation

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The fixed charge film is segmented into multiple layers with different charge densities and spatial distributions. This segmentation allows each layer to target specific regions and types of interface states, particularly those at the groove surfaces, providing more effective dark current suppression than a single uniform layer could achieve.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The multilayer fixed charge film structure provides different local qualities at different depths and positions. The film density, charge concentration, and material composition are optimized for specific locations, with higher charge densities positioned to compensate for the most severe interface states at the groove surfaces while maintaining appropriate characteristics in other regions.

Inventive Principle:

Principle #3Local quality

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 laminated fixed charge film effectively reduces dark current generation and enhances interfacial quality, while also providing an antireflection effect, improving the sensitivity and performance of the image pickup element.

Implementation Method 1

a first insulating film provided contiguously from the light-receiving surface to a wall surface and a bottom surface of the pixel separation groove

Methodology Applied

Scientific EffectAtomic layer deposition: Chemical Vapour Deposition

Implementation Method 2

a second insulating film provided on a part of the first insulating film, the part corresponding to at least the light-receiving surface

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Implementation Method 3

an insulating film (a fixed charge film) having negative fixed charge on a light-receiving surface (a back surface) of a Si substrate is formed

Methodology Applied

Scientific EffectFixed charge: Electrostatic Induction

Data Source

PatentUS11862652B2Image pickup element, method of manufacturing image pickup element, and electronic apparatus

Publication Date: 2024.01.02 SONY GROUP CORP

AI summary

An image pickup element includes: a semiconductor substrate including a photoelectric conversion section for each pixel; a pixel separation groove provided in the semiconductor substrate; and a fixed charge film provided on a light-receiving surface side of the semiconductor substrate, wherein the fixed charge film includes a first insulating film and a second insulating film, the first insulating film being provided contiguously from the light-receiving surface to a wall surface and a bottom surface of the pixel separation groove, and the second insulating film being provided on a part of the first insulating film, the part corresponding to at least the light-receiving surface.