Epitaxial Structure for CMOS Image Sensor Leakage Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors face issues with substrate leakage current and white pixels due to structural damage during etching and implanting operations, which lead to dark current leakage and defects near the photodiode region.
Innovation Solution
An epitaxial structure is disposed on the surface of the substrate to spatially separate the conductive contacts from the photodiode region, thereby avoiding damage from etching and implanting processes and reducing dark current and white pixel occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional etching and implanting operations are performed to form conductive contacts, then the image sensor structure can be manufactured, but structural damage occurs near the photodiode region causing dark current leakage and white pixels
Solution Approach 1:
An epitaxial layer is introduced as an intermediary structure between the substrate and the conductive contacts. This epitaxial layer absorbs the damage from etching and implanting operations, preventing direct damage to the photodiode region while still allowing contact formation to proceed. The epitaxial layer acts as a buffer that mediates between the manufacturing process requirements and the photodiode protection needs.
Solution Approach 2:
The patent introduces a vertical dimension by growing an epitaxial layer with specific thickness to spatially separate the damage zone from the photodiode region. By controlling the depth and thickness in the vertical dimension, the harmful effects of etching and implanting are confined to the epitaxial layer while the photodiode region remains intact at a different vertical level.
2Productivity
If conductive contacts are formed close to the photodiode region to reduce pixel area, then manufacturing efficiency is improved, but dark current leakage increases due to substrate damage
Solution Approach 1:
The epitaxial layer serves as a mediator that enables close proximity contact formation without direct damage to the photodiode. It absorbs the harmful effects of contact formation operations, allowing high pixel density to be achieved while preventing dark current leakage that would otherwise occur from substrate damage.
Solution Approach 2:
The patent segments the substrate structure by introducing a distinct epitaxial layer that is separate from both the substrate and the photodiode region. This segmentation allows the contact formation damage to be isolated in the epitaxial layer while the photodiode region maintains its integrity, enabling closer contact placement without increasing dark current.
3Reliability
If ion implanting is performed to create doped regions for contacts, then electrical conductivity is improved, but defects are created near the photodiode region causing white pixels
Solution Approach 1:
The epitaxial layer acts as an intermediary that absorbs the ion implantation damage. Ion implanting can be performed through or into the epitaxial layer to create conductive contacts without directly damaging the photodiode region, thus maintaining both contact conductivity and photodiode quality.
Solution Approach 2:
The epitaxial layer is grown in advance before contact formation operations. This preliminary action creates a protective buffer that is already in place to absorb subsequent ion implantation damage, preventing defects in the photodiode region while still allowing effective doping for contact conductivity.
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 epitaxial structure effectively minimizes substrate leakage current and maintains structural integrity, improving the yield rate of image sensor structures by protecting the photodiode region from damage during contact formation operations.
Implementation Method 1
an epitaxial structure is disposed on a surface of a substrate
Data Source
AI summary
An image sensor structure and manufacturing method thereof are provided. The image sensor structure includes a substrate with a first surface. A first doped region of a first conductivity type is in the substrate and under the first surface. A second doped region of a second conductivity type is in the substrate and under the first surface. A gate structure is on the first surface of the substrate and overlapping a boundary of the first doped region and the second doped region. The epitaxial structure is on the first surface of the substrate. A method for manufacturing an image sensor structure is also provided.