Back-Illuminated CMOS Image Sensor Light Shielding Structure

Solution Overview

Problem

Existing back-illuminated CMOS image sensors with global shutter function face issues with optical noise due to unnecessary electric charge generation in the electric-charge holding unit, as light shielding films in previous configurations do not effectively cover all surfaces, allowing light to enter and deteriorate image quality.

Innovation Solution

The implementation of a multi-layer light shielding film structure on a back-illuminated imaging device, including a first light-shielding portion between the photoelectric conversion unit and the electric-charge holding unit, a second light-shielding portion that penetrates the semiconductor substrate, and a third light-shielding portion covering part of the semiconductor substrate surface, along with a specific insulation film layer composition and thickness, to block light effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a light shielding film covers only the top surface and bottom surface of the electric-charge holding unit, then light entering from the incident surface side is blocked, but light entering from the side surfaces is not prevented

Engineering Contradiction:

Improvelight entering electric-charge holding unitVSAvoidimage quality

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The light shielding film is divided into multiple segments: a first light shielding film covering the top surface, a second light shielding film covering the bottom surface, and a third light shielding film covering the side surfaces. This segmentation allows each film to independently block light from different directions, comprehensively preventing light entry into the electric-charge holding unit.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The light shielding structure transitions from two-dimensional (top and bottom surfaces only) to three-dimensional coverage by adding side surface protection. The third light shielding film extends the protection to the vertical dimension, completely surrounding the electric-charge holding unit to block light from all directions.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Object-affected harmful factors

If the light shielding film covers only the top surface and side surfaces, then light entering from the incident surface is blocked, but light reflected off the wiring layer from the bottom surface is not prevented

Engineering Contradiction:

Improvelight entering electric-charge holding unitVSAvoidimage quality

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The light shielding film is divided into multiple segments: a first light shielding film covering the top surface, a second light shielding film covering the bottom surface, and a third light shielding film covering the side surfaces. This segmentation allows each film to independently block light from different directions, comprehensively preventing light entry into the electric-charge holding unit.

Inventive Principle:

Principle #1Segmentation

3Ease of manufacture

If the light shielding film does not cover the bottom surface, then manufacturing is simpler, but light reflected off the wiring layer enters the electric-charge holding unit

Engineering Contradiction:

Improvelight shielding film configurationVSAvoidreflected light entering electric-charge holding unit

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The light shielding film is divided into multiple segments: a first light shielding film covering the top surface, a second light shielding film covering the bottom surface, and a third light shielding film covering the side surfaces. This segmentation allows each film to independently block light from different directions, comprehensively preventing light entry into the electric-charge holding unit.

Inventive Principle:

Principle #1Segmentation

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 significantly reduces light entering the electric-charge holding unit, thereby improving image quality by minimizing optical noise and enhancing the pixel characteristics of the CMOS image sensor.

Implementation Method 1

the top surface and the bottom surface are covered by light shielding films

Methodology Applied

Scientific EffectLight blocking: Absorption (EM radiation)

Data Source

PatentUS11456325B2Imaging device, method for manufacturing imaging device, and electronic device

Publication Date: 2022.09.27 SONY SEMICON SOLUTIONS CORP

AI summary

The present disclosure relates to an imaging device, a method for manufacturing an imaging device, and an electronic device capable of reducing light entering an electric-charge holding unit in a back-illuminated imaging device. An imaging device includes: a photoelectric conversion unit; an electric-charge holding unit; a semiconductor substrate; a wiring layer; an insulation film layer; a first light-shielding film; and a second light-shielding film. The insulation film layer, the first light-shielding film, and the wiring layer are stacked on a second surface of the semiconductor substrate. The second light-shielding film includes: a first light-shielding portion extending from the first surface of the semiconductor substrate to a middle of the semiconductor substrate; a second light-shielding portion penetrating the semiconductor substrate; and a third light-shielding portion covering a part of the first surface of the semiconductor substrate. The present technology is applicable to a CMOS image sensor, for example.