Image Sensor Infrared Response via Deep Trench Isolation
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Solution Overview
Problem
Image sensors face challenges in effectively responding to infra-red radiation due to limitations in dark current parasitic signal generation and absorption efficiency, particularly in backside illumination (BSI) devices.
Innovation Solution
The integration of a semiconductor image sensor cell design featuring a semiconductor body with a capacitive deep trench isolation (CDTI) structure and buried insulated electrodes within deep trench isolations, which enhances infra-red absorption and reduces dark current parasitic signals by using a MOS trench-based structured surface biased in inversion mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If backside illumination (BSI) structure is used to improve light absorption, then absorption efficiency is improved, but dark current parasitic signal generation increases
Solution Approach 1:
The patent extracts and removes the harmful deep depletion region from the active sensing area by implementing deep trench isolation that extends through the entire substrate thickness. This isolates the backside illumination structure from generating dark current in the depleted regions, effectively taking out the harmful element while preserving the beneficial light absorption properties of the BSI architecture.
Solution Approach 2:
The patent introduces deep trench isolation structures filled with conductive or semiconductive material as an intermediary between the backside illumination surface and the underlying substrate. This intermediary layer prevents the formation of parasitic dark current while allowing the front surface to maintain efficient light absorption, thus mediating between the conflicting requirements of high absorption efficiency and low dark current.
2Object-generated harmful factors
If deep trench isolation is implemented to reduce dark current, then dark current parasitic signal is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent merges the deep trench isolation structure with the existing pixel isolation and substrate isolation functions into a single integrated structure. By combining multiple isolation functions into one unified deep trench system that extends through the entire substrate, the patent reduces the number of separate manufacturing steps while achieving comprehensive dark current suppression across all critical regions.
Solution Approach 2:
The deep trench isolation structure serves multiple functions simultaneously: it provides substrate isolation to prevent dark current, acts as pixel isolation between adjacent photodetectors, and creates the necessary electrical field configuration for backside illumination operation. This multi-functionality reduces the need for separate structures and simplifies the overall manufacturing process.
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 design significantly improves the responsiveness of the image sensor to infra-red radiation by reducing dark current-related issues, thereby enhancing detection capabilities and absorption efficiency.
Implementation Method 1
which creates a free carrier inversion channel (MOS effect)
Implementation Method 2
The present disclosure relates to an image sensor and, in particular, to an enhancement of the response of the image sensor to infra-red radiation
Data Source
AI summary
A semiconductor body of a first conductivity type and doped with a first doping level includes, at a front side surface thereof, a well of a second conductivity type and a region doped with the first conductivity type at a second doping level greater than the first doping level. An insulated vertical gate structure separates the region from the well. Buried iInsulated electrodes extend from the front side surface completely through the well and into a portion of the semiconductor body underneath the well. A conductive material portion of each buried insulated electrode is configured to receive a bias voltage and a conductive material portion of insulated vertical gate structure is configured to receive a gate voltage. The semiconductor body is delimited by a capacitive deep trench isolation that is biased at the same voltage as the buried insulated electrode.