Wafer Structure Reducing Dark Current via Segmented Oxygen
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Dark current in image sensors, caused by interface state defects and metal contaminants, degrades image quality by diffusing and combining with photo-generated charge, and existing solutions like denuded zones require additional processing steps that increase costs and reduce throughput.
Innovation Solution
A wafer structure with a substrate and epitaxial layers having specific conductivity and oxygen concentrations, where the intermediate epitaxial layer has a lower oxygen concentration than the substrate, and the device epitaxial layer has a lower dopant concentration than the intermediate layer, forming photosensitive regions and circuitry on the device epitaxial layer to reduce dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a denuded zone is formed to prevent oxygen precipitates near the interface, then dark current is reduced, but additional thermal processing steps are required which increase costs and reduce throughput
Solution Approach 1:
The substrate is divided into two distinct regions: a denuded zone free of oxygen precipitates and a bulk region containing oxygen precipitates for gettering. This segmentation allows the interface region to be protected from dark current sources while the bulk region maintains gettering functionality, eliminating the need for additional thermal processing steps.
Solution Approach 2:
Different regions of the substrate are given different oxygen concentrations tailored to their specific functions. The interface region has low oxygen concentration to prevent precipitate formation and dark current, while the bulk region has high oxygen concentration to provide gettering. This local differentiation resolves the contradiction by optimizing each region for its specific purpose without requiring additional processing.
2Reliability
If oxygen concentration is increased to improve gettering performance, then metal contaminant trapping is enhanced, but more oxygen precipitates form near the interface increasing dark current
Solution Approach 1:
The substrate is segmented into regions with different oxygen concentrations. The bulk region maintains high oxygen concentration for effective gettering of metal contaminants, while the interface region has low oxygen concentration to prevent precipitate formation that would generate dark current. This spatial segmentation allows both contradictory requirements to be satisfied simultaneously.
Solution Approach 2:
Different oxygen concentrations are applied locally to different regions based on their functional requirements. The high oxygen concentration in the bulk provides gettering performance, while the low oxygen concentration at the interface minimizes dark current. This local quality differentiation resolves the contradiction between gettering effectiveness and dark current reduction.
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 structure effectively reduces dark current by minimizing interface state defects and oxygen precipitate-induced dark current, while maintaining gettering properties and infrared sensitivity, and simplifies the fabrication process by eliminating the need for additional processing steps.
Implementation Method 1
the thickness of the intermediate epitaxial layer is greater than the diffusion length of the minority carriers corresponding to the dopant concentration of the layer
Implementation Method 2
oxygen in substrate 102 forms oxygen precipitates 112. The oxygen precipitates 112 getter metal contaminates
Data Source
AI summary
A wafer structure for an image sensor includes a substrate that has a given conductivity type, a given dopant concentration, and a given concentration of oxygen. An intermediate epitaxial layer is formed over the substrate. The intermediate epitaxial layer has the same conductivity type and the same, or substantially the same, dopant concentration as the substrate but a lower oxygen concentration than the substrate. A thickness of the intermediate epitaxial layer is greater than the diffusion length of a minority carrier in the intermediate layer. A device epitaxial layer is formed over the intermediate epitaxial layer. The device epitaxial layer has the same conductivity type but lower dopant and oxygen concentrations than the substrate.