Epitaxial Pixel Structure for Low-Noise Image Sensors
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Solution Overview
Problem
Image sensors face challenges due to lattice defects caused by impurity implantation during the formation of photoelectric conversion devices, leading to noise in image data.
Innovation Solution
The formation of a photoelectric conversion device of a second conductive type on a first epitaxial layer of a first conductive type using an epitaxial growth process, with a second epitaxial layer of the second conductive type placed between the photoelectric conversion device and the semiconductor substrate, reduces lattice defects and noise in image data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impurities are implanted into the substrate by an ion implantation process to form a photoelectric conversion device, then the photoelectric conversion device can be formed with the required conductive type, but lattice defects occur causing noise in image data
Solution Approach 1:
An intermediate layer is introduced between the substrate and the photoelectric conversion device. This intermediate layer serves as a buffer that prevents direct lattice mismatch and defect propagation, thereby reducing noise in image data while still allowing the photoelectric conversion device to be formed with the required conductive type through controlled doping processes.
Solution Approach 2:
The doping concentration and implantation energy parameters are optimized to minimize lattice damage. By carefully controlling the doping profile and using lower energy implantation followed by thermal annealing, the photoelectric conversion device achieves the necessary conductive type with reduced lattice defects and associated noise.
2Manufacturing precision
If ion implantation is used to form the photoelectric conversion device, then the conductive type can be controlled, but the lattice structure is damaged reducing image quality
Solution Approach 1:
The intermediate layer acts as a mediator that decouples the substrate lattice from the photoelectric conversion device lattice. This allows precise control of the conductive type in the photoelectric conversion device through doping, while the intermediate layer absorbs and isolates the lattice damage, preventing it from propagating to the active imaging region.
Solution Approach 2:
The intermediate layer is formed in advance before creating the photoelectric conversion device. This preliminary structure preparation enables subsequent doping processes to achieve the desired conductive type control without directly damaging the substrate lattice, as the intermediate layer is already in place to absorb the implantation damage.
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 approach minimizes lattice defects and dark current occurrences, thereby enhancing image quality by reducing noise in image data and improving the overall performance of image sensors.
Implementation Method 1
a photoelectric conversion device of a second conductive type is formed on a first epitaxial layer having a first conductive type by using an epitaxial growth process
Data Source
AI summary
An image sensor includes a plurality of pixels, wherein each of the plurality of pixels includes a first epitaxial layer disposed on a first surface of a semiconductor substrate and formed to have a first conductive type by an epitaxial growth process, a photoelectric conversion device disposed on the first epitaxial layer, the photoelectric conversion device having a second conductive type which differs from the first conductive type and a second epitaxial layer disposed between the photoelectric conversion device and a second surface of the semiconductor substrate and formed to have the second conductive type through the epitaxial growth process, wherein the photoelectric conversion device is an epitaxial layer of the second conductive type formed by the epitaxial growth process.