3D Stacked Image Sensor Fabrication via Layer Transfer
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Solution Overview
Problem
Current semiconductor technologies face challenges in fabricating three-dimensional multi-layer structures for image sensors, including reduced fill factor, misalignment issues, thermal expansion problems, and inability to sense multiple wavelengths at one pixel location, which hinder the development of efficient and cost-effective mass-produced imaging devices.
Innovation Solution
A method for fabricating a silicon/dielectric multi-layer substrate using a layer transfer process that eliminates the need for alignment and masking, allowing for the formation of a three-dimensional semiconductor device with independent wavelength control and reduced leakage current, optimized fill factor, and integrated signal processing circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional planar sensor structure with color filter array is used, then color selective output signal can be obtained, but fill factor is reduced due to signal processing circuits taking area away from photon collection
Solution Approach 1:
The patent transitions from a planar two-dimensional sensor structure to a three-dimensional stacked multi-layer structure. Multiple photodiode layers sensing different wavelengths are stacked vertically, allowing each layer to be optimized for specific wavelength ranges while increasing the overall light collection efficiency and fill factor through vertical photon capture.
Solution Approach 2:
The sensor is divided into multiple independent photodiode layers, each optimized for specific wavelength ranges (e.g., blue, green, red, infrared). This segmentation allows independent optimization of each layer's characteristics while collectively achieving full-spectrum sensing with high fill factor.
2Adaptability or versatility
If three-dimensional multi-layer structure is implemented to sense various spectrums at one pixel location, then spectral sensitivity is improved, but misalignment between layers and thermal expansion problems occur
Solution Approach 1:
The patent employs preliminary bonding of multiple photodiode layers to a common support substrate before wafer bonding. This preliminary alignment step ensures precise registration of through-silicon vias and interconnect structures across layers, preventing misalignment issues while enabling complex multi-layer integration.
Solution Approach 2:
A common support substrate is introduced as an intermediary element to which multiple photodiode layers are bonded. This intermediary provides a stable reference plane for alignment and facilitates thermal management, reducing thermal expansion problems while enabling precise multi-layer stacking.
3Adaptability or versatility
If color filter array is used in planar sensor, then wavelength selection is achieved, but significant portion of incident light is lost and only 1/3 of incident light is converted into picture information
Solution Approach 1:
The patent replaces the planar color filter array approach with a vertical stacked architecture where multiple photodiode layers sense different wavelengths at the same pixel location. This eliminates the need for color filters that block most incident light, as each wavelength range is captured by a dedicated photodiode layer, converting nearly 100% of incident light into useful signal.
Solution Approach 2:
The patent extracts and removes the color filter array component from the sensor structure. Instead of using filters to select wavelengths, dedicated photodiode layers are used to directly sense different wavelength ranges, eliminating the inherent light loss associated with filter-based wavelength selection.
4Area of stationary object
If multiple photodiode layers are stacked to convert whole light into picture information, then fill factor approaches 100%, but leakage current problems and noise cancellation issues arise
Solution Approach 1:
The patent extracts and removes the handle substrate from the final sensor structure after bonding. This allows the use of thick substrates during manufacturing for mechanical strength and alignment, while eliminating the handle substrate in the final product to reduce thermal mass and enable more efficient heat dissipation, thereby reducing leakage current.
Solution Approach 2:
The patent replaces mechanical through-silicon via structures with bonded-wafer interconnect structures. This substitution reduces stress and leakage current in the vertical interconnect paths while maintaining electrical connectivity between stacked photodiode layers.
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 enables the mass production of high-performance image sensors with improved fill factor, reduced noise, and enhanced spectral sensitivity, facilitating the development of electronic cameras with high integration and miniaturization capabilities.
Implementation Method 1
the donor wafer is bonded to a top surface of the handle wafer
Data Source
AI summary
Fabrication of a three-dimensional semiconductor structure is provided by the present disclosure. A buffer oxide film, a nitride film, and an ONO dielectric layer are formed on a handle wafer. A semiconductor layer and an oxide film are formed on a donor wafer, which is turned over and is then bonded to a handle wafer. Silicon of the donor wafer is then removed. In the same manner, blue, green, and red diode layers, and a transistor layer are sequentially formed. A metal layer is formed on the transistor layer. Inter-elements contact and pixel separation processes are performed and a support layer is bonded. The whole device is turned over and the nitride film is etched using an etch-stop layer, thus removing the handle wafer. After the elements are separated, packaging is performed to complete the device. Therefore, a back illuminated image sensor of a multi-layer structure can be provided.