Backside Illuminated Image Sensor Seed Layer Doping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Backside illuminated image sensors, particularly those using silicon-on-insulator (SOI) wafers, face challenges with dark current generation at the interface between the sensor layer and the buried oxide layer, which affects their performance and is difficult to address with conventional processing techniques.
Innovation Solution
A wafer level process involving the formation of a doped silicon seed layer with a sacrificial oxide layer, where a dopant is implanted into the seed layer in exposed pixel array areas, followed by epitaxial growth, to create a cross-sectional doping profile that reduces dark current without shorting peripheral wells, thereby improving the image sensor's ability to detect incident light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a backside illuminated image sensor is formed using a silicon-on-insulator (SOI) wafer, then the fill factor and quantum efficiency are improved, but dark current is generated at the interface between the sensor layer and the buried oxide layer
Solution Approach 1:
The patent applies parameter changes by modifying the doping concentration and type in the seed layer at the interface with the buried oxide layer. By changing the electrical parameters (doping profile) of this specific region, the dark current generation is suppressed while maintaining the backside illumination structure's quantum efficiency advantages.
Solution Approach 2:
The patent implements local quality by creating a specific doping profile only in the seed layer region adjacent to the buried oxide layer, rather than uniformly doping the entire sensor. This localized modification targets the specific area where dark current is generated, leaving other regions unchanged to preserve their functional properties.
2Object-generated harmful factors
If conventional processing techniques are used to address dark current in backside illuminated image sensors, then dark current reduction may be achieved, but die size increases or manufacturing cost increases
Solution Approach 1:
The patent applies preliminary action by incorporating the dark current reduction措施 into the seed layer formation step, which is performed early in the manufacturing process. The dopant is implanted into the seed layer before the sensor is fully fabricated, so the dark current suppression is built-in from the beginning rather than requiring additional processing steps later that would increase die size or cost.
Solution Approach 2:
The patent achieves universality by making the seed layer serve multiple functions: it provides the initial substrate for epitaxial growth and simultaneously acts as a dark current suppression layer through doping. This multi-functionality eliminates the need for separate structures or layers dedicated solely to dark current reduction, avoiding increased die size.
3Reliability
If the silicon substrate is thinned or removed to enable backside illumination, then fill factor and quantum efficiency are improved, but the sensor becomes difficult to process
Solution Approach 1:
The patent applies preliminary action by performing dopant implantation into the seed layer while the substrate is still intact and before thinning or removal occurs. This early intervention allows dark current suppression to be established during a more accessible stage of manufacturing, reducing subsequent processing difficulty.
Solution Approach 2:
The patent uses the seed layer as an intermediary structure that facilitates the transition from frontside to backside illumination processing. By establishing the doped seed layer early, it serves as a stable foundation that simplifies subsequent substrate thinning and backside processing steps.
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 process effectively reduces dark current at the interface between the sensor layer and the buried oxide layer, enhancing the image sensor's performance without increasing die size or cost, and avoiding issues like peripheral well shorting.
Implementation Method 1
implanting a dopant into the seed layer in the exposed pixel array areas
Implementation Method 2
forming an epitaxial layer over the doped seed layer
Data Source
AI summary
A backside illuminated image sensor comprises a sensor layer implementing a plurality of photosensitive elements of a pixel array, and an oxide layer adjacent a backside surface of the sensor layer. The sensor layer comprises a seed layer and an epitaxial layer formed over the seed layer, with the seed layer having a cross-sectional doping profile in which a designated dopant is substantially confined to a pixel array area of the sensor layer. The doping profile advantageously reduces dark current generated at an interface between the sensor layer and the oxide layer. The image sensor may be implemented in a digital camera or other type of digital imaging device.