Dummy Gate Pickup Structure for Image Sensor Isolation
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Solution Overview
Problem
Existing methods for isolating circuitry from photo-sensitive regions in semiconductor devices, such as shallow trench isolation and device isolation, either damage the substrate surface or are ineffective in heavily doped regions, leading to issues like dark currents and white pixel effects in image sensor arrays.
Innovation Solution
The use of a dummy gate structure, such as U-shaped, C-shaped, or L-shaped polysilicon gate structures, to partially encompass the region where the highly doped pickup region is formed, limiting its size and preventing it from extending into adjacent photodiodes, combined with sidewall spacers and ion implantation doping, to effectively isolate the circuitry and prevent stray currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shallow trench isolation is used to isolate circuitry from photo-sensitive regions, then isolation effectiveness is improved, but substrate surface damage occurs due to plasma etching
Solution Approach 1:
The harmful plasma etching process is extracted and replaced with a doping process. Instead of using plasma to create the isolation trench, the invention uses ion implantation to dope the region, eliminating the substrate damage caused by plasma while maintaining the isolation function through electrical rather than physical separation.
Solution Approach 2:
The mechanical/plasma-based isolation method is replaced with an electrical/doping-based method. The physical trench creation process is substituted with ion implantation and doping, transforming the isolation mechanism from physical separation to electrical field-based separation, thereby avoiding mechanical damage to the substrate.
2Object-affected harmful factors
If device isolation with doped semiconductor material is used to isolate circuitry, then substrate surface damage is avoided, but isolation effectiveness deteriorates in heavily doped regions
Solution Approach 1:
The invention applies different doping concentrations to different regions: a first doping concentration for the device isolation region and a second, different doping concentration for the pickup region. This local differentiation creates effective electrical isolation at the junction between regions with different doping levels, preventing stray currents while maintaining substrate integrity.
Solution Approach 2:
The invention changes the doping concentration parameter to achieve isolation. By implanting ions at specific concentrations and energies into specific regions, it creates junctions between areas of different doping levels, which form electrical barriers that prevent current leakage without requiring physical trenches.
3Productivity
If pickup region is allowed to extend freely, then circuit functionality is improved, but dark current and white pixel effects increase due to extension into adjacent photodiodes
Solution Approach 1:
The dummy gate structure is formed preliminarily before the pickup region is created. This pre-formed structure serves as a template or boundary that guides the subsequent formation of the pickup region, ensuring it stays within acceptable limits and does not encroach on adjacent photodiodes, thereby preventing dark current and white pixel effects.
Solution Approach 2:
The dummy gate structure acts as an intermediary element between the device isolation region and the pickup region. It provides a structural reference and boundary that mediates the formation process, ensuring the pickup region is properly contained while maintaining electrical connectivity where needed.
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 approach effectively isolates the circuitry from the photo-sensitive regions, reducing dark current and white pixel effects, thereby improving the accuracy of light intensity measurements in image sensor arrays without damaging the substrate surface.
Implementation Method 1
forming a highly doped pickup region into the device isolation region
Data Source
AI summary
A device includes a device isolation region formed into a semiconductor substrate, a doped pickup region formed into the device isolation region, a dummy gate structure that includes at least one structure that partially surrounds the doped pickup region, and a via connected to the doped pickup region.