Image Sensor Device Layer Recessed Cavity Crystalline Quality
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Solution Overview
Problem
CMOS image sensors have poor quantum efficiency for near-infrared (NIR) and infrared (IR) radiation due to silicon's large bandgap, leading to increased leakage current and degraded performance metrics, which can be exacerbated by crystalline defects at the interface between the substrate and the device layer during dry etching and ion implantation processes.
Innovation Solution
A method is developed to form an image sensor with a device layer recessed into a substrate, where a hard mask layer is deposited, and a sacrificial dielectric layer is used to prevent crystalline damage during ion implantation, followed by epitaxial growth of an interlayer and device layer, reducing crystalline defects and leakage current by blocking dopant diffusion and enhancing crystalline quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dry etching is performed to form a cavity in the substrate, then the cavity is formed for device layer recess, but crystalline damage is created at the cavity interface
Solution Approach 1:
A sacrificial dielectric layer is deposited lining the cavity before ion implantation. This preliminary action creates a protective barrier that prevents crystalline damage at the cavity interface during subsequent doping processes, thereby improving crystalline quality without compromising cavity formation precision
2Quantity of substance
If ion implantation is performed to dope the substrate, then dopant regions are formed, but crystalline defects are generated at the interface
Solution Approach 1:
The sacrificial dielectric layer serves as an intermediary between the ion implantation process and the substrate. It allows dopants to be delivered to the substrate while simultaneously protecting the crystalline structure from damage, thus achieving both adequate dopant concentration and maintained crystalline quality
3Quantity of substance
If dopant diffusion is allowed during processing, then doping is achieved, but low resistivity regions are created that increase leakage current
Solution Approach 1:
The sacrificial dielectric layer is selectively removed after serving its protective function. This extraction allows for controlled dopant distribution while preventing the formation of unwanted low resistivity regions that would increase leakage current, as the layer had already protected against excessive dopant diffusion during critical processing steps
4Productivity
If device layer is grown on damaged substrate surface, then device formation proceeds, but quantum efficiency and signal-to-noise ratio are degraded
Solution Approach 1:
The sacrificial dielectric layer is deposited and protective actions are taken before device layer growth. This ensures the substrate surface is protected from damage during cavity formation and doping, providing a clean interface for subsequent device layer epitaxial growth and maintaining high quantum efficiency and signal-to-noise ratio
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 reduces leakage current and improves quantum efficiency and signal-to-noise ratio by minimizing crystalline defects and dopant-induced low resistivity regions, resulting in enhanced performance of the photodetector for NIR and IR radiation detection.
Implementation Method 1
crystalline damage during ion implantation
Implementation Method 2
epitaxial growth of an interlayer and device layer
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.