Backside Illumination Image Sensor Focus Detection Accuracy

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Solution Overview

Problem

Front-side illumination image sensors face challenges in miniaturizing pixels while maintaining focus detection accuracy due to increased distance between micro lenses and photoelectric conversion units, and narrow light receiving openings which hinder the installation of focus detection pixels.

Innovation Solution

A backside illumination image sensor design that includes image-capturing pixels and focus detection pixels, with the wiring layer formed on the side opposite to the light entry side, allowing for a reduced distance between micro lenses and photoelectric conversion units, and the use of light shielding films and color filters to optimize light entry and blockage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If wiring, color filter and light shielding layer are formed between micro lens and light receiving unit in front-side illumination image sensor, then signal reading is enabled, but distance between micro lens and light receiving unit increases

Engineering Contradiction:

Improvefocus detection accuracyVSAvoiddistance between micro lens and light receiving unit

Core Design Contradiction:

Measurement precisionVSLength of stationary object

Solution Approach 1:

The patent inverts the conventional front-side illumination structure by implementing backside illumination, where light enters through the opposite side of the semiconductor substrate. This inversion allows the photoelectric conversion unit to be positioned directly beneath the micro lens without intervening wiring layers, thereby reducing the distance between the micro lens and light receiving unit while maintaining signal reading capability through rear-side wiring access.

Inventive Principle:

Principle #13The other way round (Inversion)

2Adaptability or versatility

If wiring is formed on light entry side in front-side illumination image sensor, then signal reading is enabled, but light receiving opening becomes narrow

Engineering Contradiction:

Improveintegration of focus detection pixelsVSAvoidlight receiving opening

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

By inverting the illumination direction to backside illumination, the patent relocates wiring formation to the opposite side of light entry. This allows the light receiving opening to be maximized without wiring obstruction, while wiring is formed on the rear side to enable signal reading from photoelectric conversion units, thereby facilitating the integration of focus detection pixels with larger light receiving openings.

Inventive Principle:

Principle #13The other way round (Inversion)

3Manufacturing precision

If pixels are miniaturized in front-side illumination image sensor, then resolution is improved, but focus detection accuracy deteriorates

Engineering Contradiction:

Improvepixel miniaturizationVSAvoidfocus detection accuracy

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

The patent applies backside illumination to miniaturized pixels, allowing the photoelectric conversion unit to be positioned immediately beneath each micro lens without the need for intervening wiring layers. This maintains effective optical path length even as pixel dimensions are reduced, thereby preserving focus detection accuracy while enabling continued pixel miniaturization for higher resolution.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent transitions the wiring structure from the optical path dimension (front-side) to the perpendicular dimension (backside), allowing wiring to be formed without interfering with the optical path between micro lens and photoelectric conversion unit. This dimensional reorganization enables miniaturized pixels to maintain adequate optical path length for focus detection while reducing in-plane pixel dimensions for higher resolution.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 backside illumination image sensor design improves focus detection accuracy by reducing the distance between micro lenses and photoelectric conversion units, enabling the integration of focus detection pixels even with miniaturized image sensor pixels, and optimizing light management through the use of light shielding films and color filters.

Implementation Method 1

a semiconductor layer with a photoelectric conversion unit formed at one surface

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Implementation Method 2

a color filter, through which light in a predetermined wavelength range is transmitted

Methodology Applied

Scientific EffectSelective light absorption: Absorption (EM radiation)

Implementation Method 3

a light shielding film that blocks part of light to enter the other surface of the semiconductor layer

Methodology Applied

Scientific EffectLight blocking: Absorption (EM radiation)

Data Source

PatentUS20250159380A1Backside illumination image sensor, manufacturing method thereof and image-capturing device

Publication Date: 2025.05.15 NIKON CORP

AI summary

An image sensor includes a first photoelectric conversion unit that converts light incident through a first opening to an electric charge, a second photoelectric conversion unit that converts light incident through a second opening which is smaller than the first opening to an electric charge, and a signal output wiring that outputs a first signal generated by the electric charge converted by the first photoelectric conversion unit and a second signal generated by the electric charge converted by the second photoelectric conversion unit. The second photoelectric conversion unit is disposed between the second opening and the signal output wiring.