Backside-Illuminated Image Sensor Layout for Focus Detection Pixels
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Solution Overview
Problem
Front-side illumination image sensors face challenges in miniaturization due to increased distance between micro lenses and photoelectric conversion units, affecting focus detection accuracy and making it difficult to integrate focus detection pixels with smaller light receiving openings.
Innovation Solution
A backside illumination image sensor design with focus detection pixels and image-capturing pixels, where the wiring layer is formed on the side of the semiconductor layer opposite to the light entry side, allowing for a reduced distance between micro lenses and photoelectric conversion units, and incorporating a light shielding film to block light, enabling improved focus detection accuracy.
Engineering Contradictions & Design Principles
Engineering 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 and light filtering are enabled, but distance between micro lens and light receiving unit increases, adversely affecting focus detection accuracy
Solution Approach 1:
The patent inverts the conventional front-side illumination structure to a backside illumination structure. The light receiving unit is positioned at the backside of the semiconductor substrate, and light enters through the backside surface. This inversion allows the wiring layer to be formed on the front side (light entry side) without interfering with the optical path, thereby reducing the distance between the micro lens and the light receiving unit and improving focus detection accuracy.
2Adaptability or versatility
If wiring is formed on the light entry side in front-side illumination image sensor, then signal reading is enabled, but light receiving opening becomes narrow, making it difficult to install focus detection pixels with smaller light receiving openings
Solution Approach 1:
By inverting the illumination structure to backside illumination, the wiring layer can be positioned on the front side (light entry side) without blocking the light receiving opening. The light receiving opening is formed on the backside surface, providing a clear optical path. This allows focus detection pixels with smaller light receiving openings to be integrated without conflict with the wiring structure.
3Quantity of substance
If pixels are miniaturized in front-side illumination image sensor, then pixel density increases, but focus detection accuracy deteriorates due to increased distance between micro lens and light receiving unit
Solution Approach 1:
The backside illumination structure allows pixels to be miniaturized while maintaining short distance between the micro lens and the light receiving unit. The light receiving unit is positioned at the backside surface, enabling direct light reception without passing through wiring layers. This maintains focus detection accuracy even as pixel density increases through miniaturization.
4Ease of manufacture
If light receiving opening is set apart from wiring in front-side illumination image sensor, then wiring can be formed, but opening through which light enters becomes narrow, affecting focus detection pixel installation
Solution Approach 1:
The backside illumination structure separates the wiring layer (on the front side) from the light receiving opening (on the backside), eliminating the need to set them apart on the same surface. The wiring can be freely formed on the front side without constraining the light receiving opening size on the backside, facilitating both manufacturing and focus detection pixel installation.
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 enhances focus detection accuracy and allows for the integration of focus detection pixels with larger light receiving openings, even in miniaturized pixel structures, by reducing the distance between micro lenses and photoelectric conversion units and optimizing light shielding.
Implementation Method 1
a semiconductor layer with a photoelectric conversion unit formed at one surface thereof
Implementation Method 2
a light shielding film that blocks part of light to enter the other surface of the semiconductor layer
Data Source
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.