CMOS Image Sensor Pixel Isolation via Deep Trench Polysilicon
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in effectively isolating pixel regions, leading to image distortion due to excess photoelectrons affecting neighboring photodiodes, and existing isolation methods are inefficient in preventing this issue.
Innovation Solution
A CMOS image sensor design featuring a deep trench filled with doped polysilicon between adjacent pixel regions, along with a through hole connected to a metal interconnect layer, which collects and extracts excess photoelectrons, thereby isolating pixel regions and improving sensor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional isolation methods are used between pixels, then manufacturing process is simple, but image distortion occurs due to insufficient isolation effectiveness
Solution Approach 1:
The isolation structure is divided into multiple segments: a deep trench extending to the base layer, an intermediate trench above it, and fill materials (oxide and polysilicon) in specific regions. This segmented approach creates effective isolation between adjacent pixels while maintaining manufacturing feasibility through standardized process steps.
Solution Approach 2:
The isolation structure extends vertically into the substrate with the deep trench reaching the base layer, adding a depth dimension to the isolation. This vertical extension creates effective isolation barriers that prevent charge carrier migration between pixels, solving the isolation effectiveness problem while using conventional CMOS process capabilities.
2Reliability
If deep ion implantation is used to isolate photodiodes, then isolation between adjacent photodiodes is improved, but manufacturing complexity and process difficulty increase
Solution Approach 1:
The isolation structure uses oxide fill material in the deep trench and intermediate trench regions as an intermediary barrier between adjacent photodiodes. This passive isolation structure replaces the need for deep ion implantation, achieving effective photodiode isolation through physical separation and charge collection mechanisms while maintaining ease of manufacture using standard CMOS processes.
Solution Approach 2:
The invention replaces the mechanical/chemical process of deep ion implantation with a structural approach using trenches and fill materials. Instead of modifying the photodiode region through ion implantation, the isolation is achieved through physical separation and electric field management using the trench structure and conductive fill, simplifying the manufacturing process.
3Productivity
If pixel regions are closely packed to reduce device size, then integration density is improved, but cross-talk between adjacent pixels increases
Solution Approach 1:
The deep trench isolation structure is formed preliminarily before pixel fabrication to establish isolation barriers in advance. By pre-defining the isolation regions and filling them with conductive materials, the structure prevents charge carrier migration between closely packed pixels, enabling high integration density without sacrificing pixel isolation reliability.
Solution Approach 2:
The invention converts the potentially harmful effect of closely packed pixels (increased cross-talk) into a benefit by using the close proximity to enhance the effectiveness of the isolation structure. The deep trench and intermediate trench configuration, combined with conductive fill, creates strong electric field boundaries that actually improve isolation effectiveness when pixels are densely packed, turning the density challenge into an isolation enhancement opportunity.
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 deep trench and through hole structure effectively isolate adjacent pixel regions, preventing image distortion by collecting and extracting excess photoelectrons, enhancing the overall performance of the CMOS image sensor.
Implementation Method 1
in the normal operation mode photons 101 of incident light enters into a photodiode 102 are converted into photoelectrons 103
Data Source
Figure 1~2
Figure 3A~3B
Figure 3C~3D
AI summary
A CMOS image sensor (20) includes a semiconductor substrate (200), a plurality of pixel regions in the semiconductor substrate, a deep trench (201) disposed between two adjacent pixel regions and filled with a polysilicon layer (2012) doped a first conductivity type, a plurality of well regions (2031) having a second conductivity type in each of the pixel regions, a through hole (207) connected to the polysilicon material, and an metal interconnect layer (208) connected to the through hole. The deep trench filled with the doped polysilicon layer completely isolates adjacent pixel regions. A voltage applied to the metal interconnect layer extracts excess photoelectrons generated by intensive incident light to improve the performance of the CMOS image sensor.