Backside Deep Trench Isolation With Doped Liner for Dense Pixels
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Solution Overview
Problem
In image sensors, the scaling down of device geometries leads to closer pixel sensors, necessitating improved electrical and optical isolation to reduce blooming and crosstalk, while existing deep implantation processes are complex and hinder exposure resolution due to thick photoresist layers.
Innovation Solution
A back-side deep trench isolation (BDTI) structure with a doped liner is implemented, where the BDTI structure extends from the back-side of the image sensing die into the photodiode doping layer, and a cyclic cleaning process is used to smooth the trench surfaces, followed by a low-temperature epitaxial doped liner formation and laser annealing for dopant activation, eliminating the need for front-side deep implantation and enhancing isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep implantation processes are used to improve isolation between pixels, then electrical and optical isolation is enhanced, but device complexity and fabrication difficulty increase due to thick photoresist layers hindering exposure resolution
Solution Approach 1:
The patent inverts the conventional approach by forming the deep trench isolation structure from the backside of the substrate rather than from the frontside. This allows the trench to be etched through the photodiode region to the handling substrate, eliminating the need for complex frontside deep implantation processes and thick photoresist layers, while still achieving effective electrical and optical isolation between adjacent pixels
Solution Approach 2:
The patent transitions from planar frontside processing to three-dimensional backside processing by etching deep trenches vertically through the photodiode region. This dimensional change enables the formation of isolation structures that extend deep into the substrate without requiring complex lateral patterning and thick photoresist layers, thereby simplifying the fabrication process while maintaining effective pixel isolation
2Productivity
If device geometries are scaled down to increase pixel density, then more pixels can be integrated, but electrical and optical isolation becomes more difficult to maintain, leading to increased blooming and crosstalk
Solution Approach 1:
By inverting the isolation structure formation to the backside of the substrate, the patent achieves deeper trench penetration relative to the pixel pitch. This allows effective isolation even as pixel dimensions are reduced, because the trench depth is determined by vertical etching through the photodiode region rather than by lateral implantation depth, enabling maintained isolation performance at higher pixel densities
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 solution improves exposure resolution, reduces blooming and crosstalk, and enhances the full well capacity of the photodiode by providing effective electrical and optical isolation between pixels, while simplifying the fabrication process and reducing defects.
Implementation Method 1
A cyclic cleaning process of at least two different etchants is performed alternatively to remove the defective layer
Implementation Method 2
a low-temperature epitaxial doped liner formation
Implementation Method 3
laser annealing for dopant activation
Implementation Method 4
A plurality of pixel regions are disposed within the image sensing die and respectively comprises a photodiode configured to convert radiation that enters from the back-side of the image sensor die into an electrical signal
Data Source
AI summary
The present disclosure relates to an image sensor having a photodiode surrounded by a back-side deep trench isolation (BDTI) structure, and an associated method of formation. In some embodiments, a plurality of pixel regions is disposed within an image sensing die and respectively comprises a photodiode configured to convert radiation into an electrical signal. The photodiode comprises a photodiode doping column with a first doping type surrounded by a photodiode doping layer with a second doping type that is different than the first doping type. A BDTI structure is disposed between adjacent pixel regions and extending from the back-side of the image sensing die to a position within the photodiode doping layer. The BDTI structure comprises a doped liner with the second doping type and a dielectric fill layer. The doped liner lines a sidewall surface of the dielectric fill layer.