Image Sensor Formation with Damage-Removing Cavity Etching
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Solution Overview
Problem
CMOS image sensors exhibit poor quantum efficiency (QE) for near-infrared (NIR) and infrared (IR) radiation due to silicon-based photodetectors with large bandgaps, and crystalline defects at the interface between the substrate and device layer degrade performance metrics such as signal-to-noise ratio (SNR) and increase leakage current.
Innovation Solution
A method involving a selective dry etch to form a cavity, followed by a second etch to remove crystalline damage, and epitaxial growth of a device layer with a sacrificial dielectric layer to reduce crystalline defects, using a blanket ion implantation through the dielectric layer to form a substrate implant region, and forming a photodetector in the device layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a selective dry etch is performed to form a cavity, then the device layer can be recessed into the substrate, but crystalline damage is formed at the cavity interface
Solution Approach 1:
The patent removes the damaged crystalline layer formed during etching by performing a second etch that selectively removes only the damaged layer while preserving the underlying healthy substrate. This extraction of the harmful damaged layer resolves the contradiction by maintaining precise device layer positioning while eliminating crystalline quality degradation.
Solution Approach 2:
The patent performs preliminary actions including forming a sacrificial dielectric layer before ion implantation, and conducting ion implantation through this dielectric layer to reduce crystalline damage at the interface. These preliminary protective measures prevent severe crystalline damage while still allowing the device layer to be properly recessed into the substrate.
2Reliability
If ion implantation is performed to form a substrate implant region, then dopant concentration is increased, but dopant diffusion to the device layer increases leakage current
Solution Approach 1:
The patent introduces an interlayer as an intermediary barrier between the substrate implant region and the device layer. This interlayer prevents dopant diffusion from the heavily doped substrate region to the device layer, thereby eliminating the harmful leakage current while preserving the beneficial substrate doping for carrier generation.
Solution Approach 2:
The patent segments the structure by introducing a distinct interlayer that separates the doped substrate region from the device layer. This segmentation allows the substrate to be heavily doped for carrier generation while preventing the dopants from migrating into the device layer, thus resolving the leakage current issue.
3Productivity
If the device layer is grown to fill the cavity, then the sensor structure is completed, but threading dislocation defects occur at the interface
Solution Approach 1:
The patent performs preliminary removal of the damaged crystalline layer through a second etch before growing the device layer. This preliminary action eliminates the source of threading dislocation defects at the interface, allowing the device layer to be grown without introducing harmful interface defects.
Solution Approach 2:
The patent converts the harmful crystalline damage caused by the first etch into a benefit by selectively removing only the damaged layer through a second etch. This process transforms the initially harmful etching damage into an opportunity to create a clean, defect-free interface for device layer growth.
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 method enhances crystalline quality, reducing leakage current and improving QE, SNR, and other performance metrics by minimizing crystalline defects and dopant diffusion, thereby increasing the sensor's efficiency for NIR and IR radiation detection.
Implementation Method 1
A substrate implant region is formed lining the cavity through a blanket ion implantation through the sacrificial dielectric layer
Implementation Method 2
An interlayer is epitaxially grown lining the cavity, and a device layer is epitaxially grown filling the cavity over the interlayer
Implementation Method 3
enhancing the sensor's efficiency for NIR and IR radiation detection
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a method for forming an image sensor in which a device layer has high crystalline quality. According to some embodiments, a hard mask layer is deposited covering a substrate. A first etch is performed into the hard mask layer and the substrate to form a cavity. A second etch is performed to remove crystalline damage from the first etch and to laterally recess the substrate in the cavity so the hard mask layer overhangs the cavity. A sacrificial layer is formed lining cavity, a blanket ion implantation is performed into the substrate through the sacrificial layer, and the sacrificial layer is removed. An interlayer is epitaxially grown lining the cavity and having a top surface underlying the hard mask layer, and a device layer is epitaxially grown filling the cavity over the interlayer. A photodetector is formed in the device layer.